Coo, I.F.M. de

Early-onset LBSL: How severe does it get? (Article)

2012-10-15T00:00:00Z

AimLeukoencephalopathy with brainstem and spinal cord involvement and lactate elevation (LBSL) is known as a relatively mild leukoencephalopathy. We investigated the occurrence of severe variants of LBSL with extensive brain magnetic resonance imaging (MRI) abnormalities. MethodMRIs of approximately 3,000 patients with an unknown leukoencephalopathy were retrospectively reviewed for extensive signal abnormalities of the cerebral and cerebellar white matter, posterior limb of the internal capsule, cerebellar peduncles, pyramids, and medial lemniscus. Clinical data were retrospectively collected. ResultsEleven patients fulfilled the MRI criteria (six males); six had DARS2 mutations. Clinical and laboratory findings did not distinguish between patients with and without DARS2 mutations, but MRI did. Patients with DARS2 mutations more often had involvement of structures typically affected in LBSL, including decussatio of the medial lemniscus, anterior spinocerebellar tracts, and superior and inferior cerebellar peduncles. Also, involvement of the globus pallidus was associated with DARS2 mutations. Earliest disease onset was neonatal; earliest death at 20 months. InterpretationThis study confirms the occurrence of early infantile, severe LBSL, extending the known phenotypic range of LBSL. Abnormality of specific brainstem tracts and cerebellar peduncles are MRI findings that point to the correct diagnosis. Copyright

RTTN mutations link primary cilia function to organization of the human cerebral cortex (Article)

2012-09-07T00:00:00Z

Polymicrogyria is a malformation of the developing cerebral cortex caused by abnormal organization and characterized by many small gyri and fusion of the outer molecular layer. We have identified autosomal-recessive mutations in RTTN, encoding Rotatin, in individuals with bilateral diffuse polymicrogyria from two separate families. Rotatin determines early embryonic axial rotation, as well as anteroposterior and dorsoventral patterning in the mouse. Human Rotatin has recently been identified as a centrosome-associated protein. The Drosophila melanogaster homolog of Rotatin, Ana3, is needed for structural integrity of centrioles and basal bodies and maintenance of sensory neurons. We show that Rotatin colocalizes with the basal bodies at the primary cilium. Cultured fibroblasts from affected individuals have structural abnormalities of the cilia and exhibit downregulation of BMP4, WNT5A, and WNT2B, which are key regulators of cortical patterning and are expressed at the cortical hem, the cortex-organizing center that gives rise to Cajal-Retzius (CR) neurons. Interestingly, we have shown that in mouse embryos, Rotatin colocalizes with CR neurons at the subpial marginal zone. Knockdown experiments in human fibroblasts and neural stem cells confirm a role for RTTN in cilia structure and function. RTTN mutations therefore link aberrant ciliary function to abnormal development and organization of the cortex in human individuals.

Physical activity is the key determinant of skeletal muscle mitochondrial function in type 2 diabetes (Article)

2012-09-01T00:00:00Z

Context: Conflicting data exist on mitochondrial function and physical activity in type 2 diabetes mellitus (T2DM) development. Objective: The aim was to assess mitochondrial function at different stages during T2DM development in combination with physical exercise in longstanding T2DM patients. Design and Methods: We performed cross-sectional analysis of skeletal muscle from 12 prediabetic 11 longstanding T2DM male subjects and 12 male controls matched by age and body mass index. Intervention: One-year intrasubject controlled supervised exercise training intervention was done in longstanding T2DM patients. Main Outcome Measurements: Extensive ex vivo analyses of mitochondrial quality, quantity, and function were collected and combined with global gene expression analysis and in vivo ATP production capacity after 1 yr of training. Results: Mitochondrial density, complex I activity, and the expression of Krebs cycle and oxidative phosphorylation system-related genes were lower in longstanding T2DM subjects but not in prediabetic subjects compared with controls. This indicated a reduced capacity to generate ATP in longstanding T2DM patients only. Gene expression analysis in prediabetic subjects suggested a switch from carbohydrate toward lipid as an energy source. One year of exercise training raised in vivo skeletal muscle ATP production capacity by 21 ± 2% with an increased trend in mitochondrial density and complex I activity. In addition, expression levels of β-oxidation, Krebs cycle, and oxidative phosphorylation system-related genes were higher after exercise training. Conclusions: Mitochondrial dysfunction is apparent only in inactive longstanding T2DM patients, which suggests that mitochondrial function and insulin resistance do not depend on each other. Prolonged exercise training can, at least partly, reverse the mitochondrial impairments associated with the longstanding diabetic state. Copyright

Defective NDUFA9 as a novel cause of neonatally fatal complex I disease (Article)

2012-01-01T00:00:00Z

Background: Mitochondrial disorders are associated with abnormalities of the oxidative phosphorylation (OXPHOS) system and cause significant morbidity and mortality in the population. The extensive clinical and genetic heterogeneity of these disorders due to a broad variety of mutations in several hundreds of candidate genes, encoded by either the mitochondrial DNA (mtDNA) or nuclear DNA (nDNA), impedes a straightforward genetic diagnosis. A new disease gene is presented here, identified in a single Kurdish patient born from consanguineous parents with neonatally fatal Leigh syndrome and complex I deficiency. Methods and results: Using homozygosity mapping and subsequent positional candidate gene analysis, a total region of 255.8 Mb containing 136 possible mitochondrial genes was identified. A pathogenic mutation was found in the complex I subunit encoding the NDUFA9 gene, changing a highly conserved arginine at position 321 to proline. This is the first diseasecausing mutation ever reported for NDUFA9. Complex I activity was restored in fibroblasts of the patient by lentiviral transduction with wild type but not mutant NDUFA9, confirming that the mutation causes the complex I deficiency and related disease. Conclusions: The data show that homozygosity mapping and candidate gene analysis remain an efficient way to detect mutations even in small consanguineous pedigrees with OXPHOS deficiency, especially when the enzyme deficiency in fibroblasts allows appropriate candidate gene selection and functional complementation.

Facial-muscle weakness, speech disorders and dysphagia are common in patients with classic infantile Pompe disease treated with enzyme therapy (Article)

2011-10-18T00:00:00Z

Classic infantile Pompe disease is an inherited generalized glycogen storage disorder caused by deficiency of lysosomal acid α-glucosidase. If left untreated, patients die before one year of age. Although enzyme-replacement therapy (ERT) has significantly prolonged lifespan, it has also revealed new aspects of the disease. For up to 11 years, we investigated the frequency and consequences of facial-muscle weakness, speech disorders and dysphagia in long-term survivors. Sequential photographs were used to determine the timing and severity of facial-muscle weakness. Using standardized articulation tests and fibreoptic endoscopic evaluation of swallowing, we investigated speech and swallowing function in a subset of patients. This study included 11 patients with classic infantile Pompe disease. Median age at the start of ERT was 2.4 months (range 0.1-8.3 months), and median age at the end of the study was 4.3 years (range 7.7 months -12.2 years). All patients developed facial-muscle weakness before the age of 15 months. Speech was studied in four patients. Articulation was disordered, with hypernasal resonance and reduced speech intelligibility in all four. Swallowing function was studied in six patients, the most important findings being ineffective swallowing with residues of food (5/6), penetration or aspiration (3/6), and reduced pharyngeal and/or laryngeal sensibility (2/6). We conclude that facial-muscle weakness, speech disorders and dysphagia are common in long-term survivors receiving ERT for classic infantile Pompe disease. To improve speech and reduce the risk for aspiration, early treatment by a speech therapist and regular swallowing assessments are recommended.

A mutation in the Golgi Qb-SNARE gene GOSR2 causes progressive myoclonus epilepsy with early ataxia (Article)

2011-05-13T00:00:00Z

The progressive myoclonus epilepsies (PMEs) are a group of predominantly recessive disorders that present with action myoclonus, tonic-clonic seizures, and progressive neurological decline. Many PMEs have similar clinical presentations yet are genetically heterogeneous, making accurate diagnosis difficult. A locus for PME was mapped in a consanguineous family with a single affected individual to chromosome 17q21. An identical-by-descent, homozygous mutation in GOSR2 (c.430G>T, p.Gly144Trp), a Golgi vesicle transport gene, was identified in this patient and in four apparently unrelated individuals. A comparison of the phenotypes in these patients defined a clinically distinct PME syndrome characterized by early-onset ataxia, action myoclonus by age 6, scoliosis, and mildly elevated serum creatine kinase. This p.Gly144Trp mutation is equivalent to a loss of function and results in failure of GOSR2 protein to localize to the cis-Golgi.

Long-term follow-up and treatment in nine boys with X-linked creatine transporter defect (Article)

2011-05-10T00:00:00Z

The creatine transporter (CRTR) defect is a recently discovered cause of X-linked intellectual disability for which treatment options have been explored. Creatine monotherapy has not proved effective, and the effect of treatment with L-arginine is still controversial. Nine boys between 8 months and 10 years old with molecularly confirmed CRTR defect were followed with repeated1H-MRS and neuropsychological assessments during 4-6 years of combination treatment with creatine monohydrate, L-arginine, and glycine. Treatment did not lead to a significant increase in cerebral creatine content as observed with H1-MRS. After an initial improvement in locomotor and personal-social IQ subscales, no lasting clinical improvement was recorded. Additionally, we noticed an age-related decline in IQ subscales in boys affected with the CRTR defect.

Long-term follow-up of type 1 lissencephaly: Survival is related to neuroimaging abnormalities (Article)

2011-05-01T00:00:00Z

Aim: To evaluate survival, clinical, and genetic characteristics of all patients with classic or type 1 lissencephaly born between 1972 and 1990 in the Netherlands, who at the time were enrolled in an observational study. Method: We re-evaluated 24 patients (11 males, 13 females) for long-term follow-up and survival information. Results: Mean length of follow-up was 14years (SD 9y 8mo). Eleven patients were alive at follow-up. All patients showed severe intellectual disability, intractable epilepsy, and complete dependency on care. Life expectancy was related to the severity of the lissencephaly on neuroimaging. Molecular analysis of the LIS1 gene was not possible at the time of the original study and was now requested by eight parents. This revealed a pathogenic nonsense mutation or deletion in seven patients. Interpretation Our study provides information about the long-term course of lissencephaly and the relationship between lissencephaly severity and prognosis. It also shows that renewed attention to genetic counselling remains valued by families of patients with a severe congenital neurological disease. © The Authors. Developmental Medicine & Child Neurology

Lung disease in FLNA mutation: Confirmatory report (Article)

2011-05-01T00:00:00Z

Recently in this journal, Masurel-Paulet et al. reported the association between pulmonary disease and a mutation in X-linked FLNA in a male patient. We confirm this association in a female patient, showing that this complication is not sex-specific. Our patient has a FLNA missense mutation (c.220G > A) and presented with cerebral periventricular nodular heterotopia, cardiovascular abnormalities, and pulmonary disease consisting of lobar emphysema of the right middle pulmonary lobe with severe malacia of the right sided bronchus intermedius. Surgical resection of the right middle lobe was necessary and she had long-term oxygen dependency. Symptoms improved with age.

Riboflavin-responsive oxidative phosphorylation complex i deficiency caused by defective ACAD9: New function for an old gene (Article)

2011-01-01T00:00:00Z

Mitochondrial complex I deficiency is the most common oxidative phosphorylation defect. Mutations have been detected in mitochondrial and nuclear genes, but the genetics of many patients remain unresolved and new genes are probably involved. In a consanguineous family, patients presented easy fatigability, exercise intolerance and lactic acidosis in blood from early childhood. In muscle, subsarcolemmal mitochondrial proliferation and a severe complex I deficiency were observed. Exercise intolerance and complex I activity was improved by a supplement of riboflavin at high dosage. Homozygosity mapping revealed a candidate region on chromosome three containing six mitochondria-related genes. Four genes were screened for mutations and a homozygous substitution was identified in ACAD9 (c.1594C>T), changing the highly conserved arginine-532 into tryptophan. This mutation was absent in 188 ethnically matched controls. Protein modelling suggested a functional effect due to the loss of a stabilizing hydrogen bond in an α-helix and a local flexibility change. To test whether the ACAD9 mutation caused the complex I deficiency, we transduced fibroblasts of patients with wild-type and mutant ACAD9. Wild-type, but not mutant, ACAD9 restored complex I activity. An unrelated patient with the same phenotype was compound heterozygous for c.380G>A and c.1405C>T, changing arginine-127 into glutamine and arginine-469 into tryptophan, respectively. These amino acids were highly conserved and the substitutions were not present in controls, making them very probably pathogenic. Our data support a new function for ACAD9 in complex I function, making this gene an important new candidate for patients with complex I deficiency, which could be improved by riboflavin treatment.

The EEG response to pyridoxine-IV neither identifies nor excludes pyridoxine-dependent epilepsy (Article)

2010-12-01T00:00:00Z

Purpose: Pyridoxine-dependent epilepsy (PDE) is characterized by therapy-resistant seizures (TRS) responding to intravenous (IV) pyridoxine. PDE can be identified by increased urinary alpha-aminoadipic semialdehyde (α-AASA) concentrations and mutations in the ALDH7A1 (antiquitin) gene. Prompt recognition of PDE is important for treatment and prognosis of seizures. We aimed to determine whether immediate electroencephalography (EEG) alterations by pyridoxine-IV can identify PDE in neonates with TRS. Methods: In 10 neonates with TRS, we compared online EEG alterations by pyridoxine-IV between PDE (n = 6) and non-PDE (n = 4). EEG segments were visually and digitally analyzed for average background amplitude and total power and relative power (background activity magnitude per frequency band and contribution of the frequency band to the spectrum). Results: In 3 of 10 neonates with TRS (2 of 6 PDE and 1 of 4 non-PDE neonates), pyridoxine-IV caused flattening of the EEG amplitude and attenuation of epileptic activity. Quantitative EEG alterations by pyridoxine-IV consisted of (1) decreased central amplitude, p < 0.05 [PDE: median -30% (range -78% to -3%); non-PDE: -20% (range -45% to -12%)]; (2) unaltered relative power; (3) decreased total power, p < 0.05 [PDE: -31% (-77% to -1%); -27% (-73% to -13%); -35% (-56% to -8%) and non-PDE: -16% (-43% to -5%); -28% (-29% to -17%); -26% (-54% to -8%), in delta-, theta- and beta-frequency bands, respectively]; and (4) similar EEG responses in PDE and non-PDE. Discussion: In neonates with TRS, pyridoxine-IV induces nonspecific EEG responses that neither identify nor exclude PDE. These data suggest that neonates with TRS should receive pyridoxine until PDE is fully excluded by metabolic and/or DNA analysis.

Absence epilepsy and periventricular nodular heterotopia (Article)

2010-09-01T00:00:00Z

We report a case of a girl who presented with typical absence seizures at age of 4.5 years. EEG showed absence seizures of sudden onset with 3 Hz spike-and-waves that also correlated with the clinical absences. The seizure semiology included subtle deviation of the eyes which prompted MRI investigation of the brain. This showed a periventricular nodular heterotopia in the mid to anterior horn of the right lateral ventricle. Although possibly coincidental, periventricular heterotopia are considered to be epileptogenic and this association has been reported once before. Migration disorders, such as in the periventricular heterotopia of our patient, may influence the formation and excitability of the striato-thalamo-cortical network involved in the generation of 3 Hz spike-waves.

Defective complex I assembly due to C20orf7 mutations as a new cause of Leigh syndrome (Article)

2010-08-01T00:00:00Z

Background: Leigh syndrome is an early onset, progressive, neurodegenerative disorder with developmental and motor skills regression. Characteristic magnetic resonance imaging abnormalities consist of focal bilateral lesions in the basal ganglia and/or the brainstem. The main cause is a deficiency in oxidative phosphorylation due to mutations in an mtDNA or nuclear oxidative phosphorylation gene. Methods and results: A consanguineous Moroccan family with Leigh syndrome comprise 11 children, three of which are affected. Marker analysis revealed a homozygous region of 11.5 Mb on chromosome 20, containing 111 genes. Eight possible mitochondrial candidate genes were sequenced. Patients were homozygous for an unclassified variant (p.P193L) in the cardiolipin synthase gene (CRLS1). As this variant was present in 20% of a Moroccan control population and enzyme activity was only reduced to 50%, this could not explain the rare clinical phenotype in our family. Patients were also homozygous for an amino acid substitution (p.L159F) in C20orf7, a new complex I assembly factor. Parents were heterozygous and unaffected sibs heterozygous or homozygous wild type. The mutation affects the predicted S-adenosylmethionine (SAM) dependent methyltransferase domain of C20orf7, possibly involved in methylation of NDUFB3 during the assembly process. Blue native gel electrophoresis showed an altered complex I assembly with only 30-40% of mature complex I present in patients and 70-90% in carriers. Conclusions: A new cause of Leigh syndrome can be a defect in early complex I assembly due to C20orf7 mutations.

KBG syndrome associated with periventricular nodular heterotopia (Article)

2010-07-01T00:00:00Z

Unbalanced der(5)t(5;20) translocation associated with megalencephaly, perisylvian polymicrogyria, polydactyly and hydrocephalus (Article)

2010-06-01T00:00:00Z

The combination of megalencephaly, perisylvian polymicrogyria, polydactyly and hydrocephalus (MPPH) is a rare syndrome of unknown cause. We observed two first cousins affected by an MPPH-like phenotype with a submicroscopic chromosome 5q35 deletion as a result of an unbalanced der(5)t(5;20)(q35.2;q13.3) translocation, including the NSD1 Sotos syndrome locus. We describe the phenotype and the deletion breakpoints of the two MPPH-like patients and compare these with five unrelated MPPH and Sotos patients harboring a 5q35 microdeletion. Mapping of the breakpoints in the two cousins was performed by MLPA, FISH, high density SNP-arrays and Q-PCR for the 5q35 deletion and 20q13 duplication. The 5q35 deletion area of the two cousins almost completely overlaps with earlier described patients with an atypical Sotos microdeletion, except for the DRD1 gene. The five unrelated MPPH patients neither showed submicroscopic chromosomal aberrations nor DRD1 mutations. We reviewed the brain MRI of 10 Sotos patients and did not detect polymicrogyria in any of them. In our two cousins, the MPPH-like phenotype is probably caused by the contribution of genes on both chromosome 5q35 and 20q13. Some patients with MPPH may harbor a submicroscopic chromosomal aberration and therefore high-resolution array analysis should be part of the diagnostic workup.

Periventricular nodular heterotopia and distal limb deficiency: A recurrent association (Article)

2010-04-01T00:00:00Z

Malformations of cerebral cortical development, in particular periventricular nodular heterotopia(PNH), and distal transverse limb deficiency have been reported as associated congenital anomalies. Patients with PNH and transverse limb deficiency can be classified as having amniotic band sequence or Adams - Oliver syndrome (AOS). Controversy exists whether these should be considered separate entities. In some AOS patients, autosomal recessive inheritance has been shown, but in most patients causes are unknown, and both environmental and genetic factors have been implicated. We present three patients with PNH and distal transverse limb deficiency to support the hypothesis that these should be considered part of one group of disorders, and highlight the variable severity of the clinical and neuroradiological phenotype. Chromosome abnormalities were excluded by copy number analysis on 250K SNP microarray data.Research done on limb deficiency as on PNH caused by mutations in known genes, suggests the involvement of vascular developmental pathways. The combination of limb deficiency and PNH may have a common causative mechanism. Recognition and grouping of patients with this combination of abnormalities will help elucidating the cause.

Patients with Leber hereditary optic neuropathy fail to compensate impaired oxidative phosphorylation (Article)

2010-02-01T00:00:00Z

Ninety-five percent of Leber hereditary optic neuropathy (LHON) patients carry a mutation in one out of three mtDNA-encoded ND subunits of complex I. Penetrance is reduced and more male than female carriers are affected. To assess if a consistent biochemical phenotype is associated with LHON expression, complex I- and complex II-dependent adenosine triphosphate synthesis rates (CI-ATP, CII-ATP) were determined in digitonin-permeabilized peripheral blood mononuclear cells (PBMCs) of thirteen healthy controls and for each primary mutation of a minimum of three unrelated patients and of three unrelated carriers with normal vision and were normalized per mitochondrion (citrate synthase activity) or per cell (protein content). We found that in mitochondria, CI-ATP and CII-ATP were impaired irrespective of the primary LHON mutation and clinical expression. An increase in mitochondrial density per cell compensated for the dysfunctional mitochondria in LHON carriers but was insufficient to result in a normal biochemical phenotype in early-onset LHON patients.

Combined cardiological and neurological abnormalities due to filamin A gene mutation (Article)

2010-01-01T00:00:00Z

Background: Cardiac defects can be the presenting symptom in patients with mutations in the X-linked gene FLNA. Dysfunction of this gene is associated with cardiac abnormalities, especially in the left ventricular outflow tract, but can also cause a congenital malformation of the cerebral cortex. We noticed that some patients diagnosed at the neurogenetics clinic had first presented to a cardiologist, suggesting that earlier recognition may be possible if the diagnosis is suspected. Methods and results: From the Erasmus MC cerebral malformations database 24 patients were identified with cerebral bilateral periventricular nodular heterotopia (PNH) without other cerebral cortical malformations. In six of these patients, a pathogenic mutation in FLNA was present. In five a cardiac defect was also found in the outflow tract. Four had presented to a cardiologist before the cerebral abnormalities were diagnosed. Conclusions: The cardiological phenotype typically consists of aortic or mitral regurgitation, coarctation of the aorta or other left-sided cardiac malformations. Most patients in this category will not have a FLNA mutation, but the presence of neurological complaints, hyperlaxity of the skin or joints and/or a family history with similar cardiac or neurological problems in a possibly X-linked pattern may alert the clinician to the possibility of a FLNA mutation.

Quality of life in patients with leber hereditary optic neuropathy (Article)

2009-12-01T00:00:00Z

PURPOSE. Leber hereditary optic neuropathy (LHON) is an inherited mitochondrial optic neuropathy characterized by bilateral, severe loss of central vision. In this study, the first formal assessment was conducted of visual disability in affected and unaffected individuals from molecularly confirmed LHON pedigrees. METHODS. Four hundred two LHON carriers-196 affected and 206 unaffected-from 125 genealogically distinct pedigrees were prospectively interviewed using the well-validated visual function index (VF-14) questionnaire: m.3460G>A (n = 71), m.11778G>A (n = 270), and m.14484T>C (n = 61). RESULTS. The mean age of onset of visual loss was 27.9 years (SD, 14.9) and mean disease duration was 15.5 years (SD, 15.4), with 74.5% of the affected subjects being men. The mean VF-14 score was 25.1 (SD, 20.8) in the affected patients, compared with 97.3 (SD, 7.1) in the unaffected carriers. Within the affected group, VF-14 score did not worsen with increasing disease duration and individuals with the m.14484T>C mutation had higher VF-14 scores compared with those in the m.3460G>A and m.11778G>A groups. Reading small print and reading a newspaper or book were the two VF-14 items that presented the greatest difficulty. CONCLUSIONS. LHON has a severe negative impact on quality of life and has the worst VF-14 score when compared with other previously studied ophthalmic disorders. However, affected LHON carriers can be reassured that their level of visual impairment is unlikely to progress with time. The VF-14 questionnaire will be a useful tool for assessing the natural history of LHON and measuring outcome in future treatment trials.

The unfolding clinical spectrum of POLG mutations (Article)

2009-11-01T00:00:00Z

Background: Mutations in the DNA polymerase-γ (POLG) gene are a major cause of clinically heterogeneous mitochondrial diseases, associated with mtDNA depletion and multiple deletions. Objective: To determine the spectrum of POLG mutations in our Dutch patient cohort, to evaluate the pathogenicity of novel mutations, and to establish genotype-phenotype correlations. Results: The authors identified 64 predominantly recessive mutations in 37 patients from a total of 232 patients, consisting of 23 different mutations. The substitution p.A467T was most frequently observed (n = 23), but was as frequent in childhood cases as in adult cases. Five new pathogenic recessive mutations, p.Lys925ArgfsX42, p.R275X, p.G426S, p.A804T and p.R869Q were identified. The known dominant chronic progressive external ophthalmoplegia (CPEO) mutation p.R943H was for the first time associated with premature ovarian failure as well. In 19 patients the authors identified only a single recessive mutation, or a sequence variant with unclear clinical significance. The data substantiate earlier observations that in POLG patients a fatal status epilepticus and liver failure can be triggered by sodium valproate. It is therefore important to exclude POLG mutations before administering this treatment. Conclusion: The clinical features of the patient are the most important features to select putative POLG mutation carriers and not the presence of mtDNA deletions or OXPHOS (oxidative phosphorylation) activity. The authors conclude that POLG mutations are an important cause of heterogeneous mitochondrial pathology and that more accurate genotype-phenotype correlations allow a more rapid genetic diagnosis and improved prognosis for mutation carriers.

Geneenvironment interactions in Leber hereditary optic neuropathy (Article)

2009-09-01T00:00:00Z

Leber hereditary optic neuropathy (LHON) is a genetic disorder primarily due to mutations of mitochondrial DNA (mtDNA). Environmental factors are thought to precipitate the visual failure and explain the marked incomplete penetrance of LHON, but previous small studies have failed to confirm this to be the case. LHON has no treatment, so identifying environmental triggers is the key to disease prevention, whilst potentially revealing new mechanisms amenable to therapeutic manipulation. To address this issue, we conducted a large, multicentre epidemiological study of 196 affected and 206 unaffected carriers from 125 LHON pedigrees known to harbour one of the three primary pathogenic mtDNA mutations: m.3460G>A, m.11778G>A and m.14484T>C. A comprehensive history of exposure to smoking, alcohol and other putative environmental insults was collected using a structured questionnaire. We identified a strong and consistent association between visual loss and smoking, independent of gender and alcohol intake, leading to a clinical penetrance of 93 in men who smoked. There was a trend towards increased visual failure with alcohol, but only with a heavy intake. Based on these findings, asymptomatic carriers of a LHON mtDNA mutation should be strongly advised not to smoke and to moderate their alcohol intake.

Mutation in the AP4M1 Gene Provides a Model for Neuroaxonal Injury in Cerebral Palsy (Article)

2009-07-10T00:00:00Z

Cerebral palsy due to perinatal injury to cerebral white matter is usually not caused by genetic mutations, but by ischemia and/or inflammation. Here, we describe an autosomal-recessive type of tetraplegic cerebral palsy with mental retardation, reduction of cerebral white matter, and atrophy of the cerebellum in an inbred sibship. The phenotype was recorded and evolution followed for over 20 years. Brain lesions were studied by diffusion tensor MR tractography. Homozygosity mapping with SNPs was performed for identification of the chromosomal locus for the disease. In the 14 Mb candidate region on chromosome 7q22, RNA expression profiling was used for selecting among the 203 genes in the area. In postmortem brain tissue available from one patient, histology and immunohistochemistry were performed. Disease course and imaging were mostly reminiscent of hypoxic-ischemic tetraplegic cerebral palsy, with neuroaxonal degeneration and white matter loss. In all five patients, a donor splice site pathogenic mutation in intron 14 of the AP4M1 gene (c.1137+1G→T), was identified. AP4M1, encoding for the μ subunit of the adaptor protein complex-4, is involved in intracellular trafficking of glutamate receptors. Aberrant GluRδ2 glutamate receptor localization and dendritic spine morphology were observed in the postmortem brain specimen. This disease entity, which we refer to as congenital spastic tetraplegia (CST), is therefore a genetic model for congenital cerebral palsy with evidence for neuroaxonal damage and glutamate receptor abnormality, mimicking perinatally acquired hypoxic-ischemic white matter injury.

Movement disorder and neuronal migration disorder due to ARFGEF2 mutation (Article)

2009-04-22T00:00:00Z

We report a child with a severe choreadystonic movement disorder, bilateral periventricular nodular heterotopia (BPNH), and secondary microcephaly based on compound heterozygosity for two new ARFGEF2 mutations (c.2031_2038dup and c.3798_3802del), changing the limited knowledge about the phenotype. The brain MRI shows bilateral hyperintensity of the putamen, BPNH, and generalized atrophy. Loss of ARFGEF2 function affects vesicle trafficking, proliferation/apoptosis, and neurotransmitter receptor function. This can explain BPNH and microcephaly. We hypothesize that the movement disorder and the preferential damage to the basal ganglia, specifically to the putamen, may be caused by an increased sensitivity to degeneration, a dynamic dysfunction due to neurotransmitter receptor mislocalization or a combination of both.

Filamin a mutation, a common cause for periventricular heterotopia, aneurysms and cardiac defects (Article)

2009-04-01T00:00:00Z

Filamin A is an important gene involved in the development of the brain, heart, connective tissue and blood vessels. A case is presented illustrating the challenge in recognising patients with filamin A mutations. The patient, a 71-year-old woman, was known to have heart valve disease and bilateral periventricular nodular heterotopia when she died of a subarachnoid haemorrhage. Autopsy showed typical cerebral bilateral periventricular heterotopia and vascular abnormalities. Postmortally, the diagnosis of a filamin A mutation was confirmed. Recognition during life may prevent cardiovascular problems and provide possibilities for genetic counselling.

Termination of damaged protein repair defines the occurrence of symptoms in carriers of the m.3243A>G tRNALeu mutation (Article)

2008-08-01T00:00:00Z

Background: The m.3243A>G mutation in the mitochondrial tRNALeu(UUR)gene is an example of a mutation causing a very heterogeneous phenotype. It is the most frequent cause (80%) of the MELAS syndrome (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes), but it can also lead in addition or separately to type 2 diabetes, deafness, renal tubulopathy and/or cardiomyopathy. Methods: To identify pathogenic processes induced by this mutation, we compared global gene expression levels of muscle biopsies from affected and unaffected mutation carriers with controls. Results and conclusions: Gene expression changes were relatively subtle. In the asymptomatic group 200 transcripts were upregulated and 12 were downregulated, whereas in the symptomatic group 15 transcripts were upregulated and 52 were downregulated. In the asymptomatic group, oxidative phosphorylation (OXPHOS) complex I and IV genes were induced. Protein turnover and apoptosis were elevated, most likely due to the formation of dysfunctional and reactive oxygen species (ROS) damaged proteins. These processes returned to normal in symptomatic patients. Components of the complement system were upregulated in both groups, but the strongest in the symptomatic group, which might indicate muscle regeneration - most likely, protein damage and OXPHOS dysfunction stimulate repair (protein regeneration) and metabolic adaptation (OXPHOS). In asymptomatic individuals these processes suffice to prevent the occurrence of symptoms. However, in affected individuals the repair process terminates, presumably because of excessive damage, and switches to muscle regeneration, as indicated by a stronger complement activation. This switch leaves increasingly damaged tissue in place and muscle pathology becomes manifest. Therefore, the expression of complement components might be a marker for the severity and progression of MELAS clinical course.

Extensive cerebral infarction in the newborn due to incontinentia pigmenti (Article)

2008-07-01T00:00:00Z

Introduction: Incontinentia pigmenti (IP) is a rare X-linked dominant neuroectodermal multisystem disorder characterized by skin lesions following Blaschko lines. In almost all patients the skin is involved and in 30-50% the central nervous system (CNS) is. Vascular occlusive phenomena probably play a role in CNS involvement. Whether these vascular changes are based on macro- or microvascular disease in the neonatal presentation is not fully understood. Patients and methods: We describe two patients with IP with neonatal seizures related to cerebral infarction. In comparison, we reviewed reports of ischaemic cerebrovascular injury in neonatal IP. Results: No descriptions of documented large artery occlusion in neonatal IP was found in the literature. One of our patients showed striatal arteriopathy, never described before in IP. Extensive injury in one of our cases was heterogeneous, mixing healthy with diseased areas within large arterial fields. Conclusions: We postulate that neonatal cerebral infarction in IP is a macrovascular disorder of medium sized or small arteries. The pattern of arterial involvement might follow hypothetical brain Blaschko lines. The extent of cerebral involvement probably results from genetic mosaicism in which Lyonisation leads to endothelial apoptosis, similar to the process in the skin.

Cortical brain malformations: Effect of clinical, neuroradiological, and modern genetic classification (Article)

2008-03-01T00:00:00Z

Background: Malformations of cortical development (MCDs) are a major source of handicap. Much progress in understanding the genetic causes has been made recently. The number of affected children in whom a molecularly confirmed diagnosis can be made is unclear. Objective: To evaluate the etiology of MCDs in children and the effect of a combined radiological, clinical, and syndrome classification. Design: A case series of 113 children with a radiological diagnosis of MCD from January 1, 1992, to January 1, 2006. Setting: The Erasmus Medical Center-Sophia Children's Hospital, a secondary and tertiary referral center. Patients: Patients with MCD underwent a complete radiological, clinical, and neurological assessment and testing for known genes involved in the pathogenesis of MCD as appropriate for their phenotype. Results: We established an etiological diagnosis in 45 of 113 cases (40%). For 21 patients (19%), this included molecular and/or genetic confirmation (Miller-Dieker syndrome; LIS1, DCX, FLNA, EIF2AK3, or KIAA1279 mutations; or an inborn error of metabolism). In 17 (15%), a syndrome with an unknown genetic defect was diagnosed. In 7 patients (6%), we found evidence of a gestational insult. Of the remaining 68 patients, 34 probably have a yet-unknown genetic disorder based on the presence of multiple congenital anomalies (15 patients), a family history with multiple affected persons (12 patients), or consanguineous parents (7 patients). Conclusions: In our cohort, combining diagnostic molecular testing with clinical, radiological, and genetic classification; syndrome identification; and family study provided a diagnosis in 40% of the cases of MCD. This contributes to the possibility of prenatal diagnosis and improved patient treatment and disease management.

A simplified and reliable assay for complex I in human blood lymphocytes (Article)

2007-09-30T00:00:00Z

Complex I activity of the mitochondrial respiratory chain is difficult to measure in blood lymphocytes because of the limited access of substrates to the enzyme complex in these cells. The results of the present study show that permeabilization of human blood lymphocytes in the presence of protease inhibitors by three cycles of freeze-thawing enables reproducible detection of the rotenone-sensitive complex I activity. To that end, the water-soluble coenzyme Q10analogue CoQ1and a relatively high concentration of blood lymphocytes were combined in small quartz cuvettes so that the amount of blood needed for this assay remained low. The relationship between the initial rate of NADH oxidation by complex I and the protein concentration was quasi-linear. The fractional inhibition of the total NADH:CoQ1oxidoreductase by a saturating concentration of rotenone decreased sharply at CoQ1concentrations higher than 20 μM, which is indicative, but does not prove the involvement of a second CoQ1binding site at complex I. Since the present complex I assay requires only a small amount of blood, the functionality of this important respiratory chain complex can be assessed in an easy and reliable manner not only in adult patients but also in children suspected to have a mitochondrial disease.

A MELAS-associated ND1 mutation causing Leber hereditary optic neuropathy and spastic dystonia (Article)

2007-06-01T00:00:00Z

Objective: To report a novel mutation that is associated with Leber hereditary optic neuropathy (LHON) within the same family affected by spastic dystonia. Design: Leber hereditary optic neuropathy is a mitochondrial disorder characterized by isolated central visual loss. Of patients with LHON, 95% carry a mutation in 1 of 3 mitochondrial DNA-encoded complex I genes. The complete mitochondrial DNA was screened for mutations in a patient with LHON without 1 of these 3 primary mutations. The heteroplasmy level and biochemical consequence of the mutation were determined. Results: A pathogenic 3697G>A/ND1 mutation was detected and seemed associated with an isolated complex I deficiency. This family has similar clinical characteristics as the previously described families with LHON and dystonia with an ND6 mutation. Conclusions: The 3697G>A/ND1 mitochondrial DNA mutation causes the LHON and spastic dystonia phenotype in the same family. This mutation can also cause MELAS syndrome (which encompasses mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke), and other genetic factors may contribute to the clinical expression.

Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome (Article)

2007-04-01T00:00:00Z

Williams Syndrome (WS, [MIM 194050]) is a disorder caused by a hemizygous deletion of 25-30 genes on chromosome 7q11.23. Several of these genes including those encoding cytoplasmic linker protein-115 (CYLN2) and general transcription factors (GTF2I and GTF2IRD1) are expressed in the brain and may contribute to the distinct neurological and cognitive deficits in WS patients. Recent studies of patients with partial deletions indicate that hemizygosity of GTF2I probably contributes to mental retardation in WS. Here we investigate whether CYLN2 and GTF2IRD1 contribute to the motoric and cognitive deficits in WS. Behavioral assessment of a new patient in which STX1A and LIMK1, but not CYLN2 and GTF2IRD1, are deleted showed that his cognitive and motor coordination functions were significantly better than in typical WS patients. Comparative analyses of gene specific CYLN2 and GTF2IRD1 knockout mice showed that a reduced size of the corpus callosum as well as deficits in motor coordination and hippocampal memory formation may be attributed to a deletion of CYLN2, while increased ventricle volume can be attributed to both CYLN2 and GTF2IRD1. We conclude that the motor and cognitive deficits in Williams Syndrome are caused by a variety of genes and that heterozygous deletion of CYLN2 is one of the major causes responsible for such dysfunctions.

mtDNA point mutations are present at various levels of heteroplasmy in human oocytes. (Article)

2007-03-01T00:00:00Z

Little is known about the load of mutations and polymorphisms in the mitochondrial DNA (mtDNA) of human oocytes and the possible effect these mutations may have during life. To investigate this, we optimised at the single cell level the recently developed method to screen the entire mtDNA for mainly heteroplasmic mutations by denaturing high performance liquid chromatography analysis. This method is sensitive (approximately 1% heteroplasmy detectable), specific and rapid. The entire mtDNA of 26 oocytes of 13 women was screened by this method. Ten different heteroplasmic mutations, of which only one was located in the D-loop and two were observed twice, were detected in seven oocytes with mutation loads ranging from <5% to 50%. From eight women >1 oocyte was received and in four of them heteroplasmic differences between oocytes of the same woman were observed. In one of these four, two homoplasmic D-loop variants were also detected. Additionally, four oocytes of a single woman were sequenced using the MitoChip (which lacks the D-loop region), but all sequences were identical. It is concluded that heteroplasmic mtDNA mutations are common in oocytes and that, depending on the position and mutation load, they might increase the risk of developing OXPHOS disease early or later in life.

Genetic defects in patients with mitochondrial encephalomyopathies (Doctoral Thesis)

2005-05-20T00:00:00Z

Summary This thesis is a contribution to the fast growing field devoted to the improvement of the diagnostics in patients with mitochondrial encephalomyopathies at the DNA level and is inspired amongst others by the hypothesis of intergenomic crosstalk between the nuclear genome (e.g. the 24 kDa subunit of complex I) and the mitochondrial genome. It presents the results of clinical, biochemical and molecular genetic studies that have been performed at the Department of Human Genetics, University Hospital Nijmegen, Nijmegen; at the Division of Genetics, University of Maastricht, Maastricht; at the Department of Neurology, Erasmus MC -University Medical Center Rotterdam, The Netherlands and at the Institute of Neurology, The National Hospital, Queen Square, London, UK (Introduction, Chapter 1). In this thesis, different strategies are described to discriminate the cause of a mitochondrial encephalomyopathy to be located either in the mitochondrial or in the nuclear genome (Chapter 2-7). First a PCR-based test is described to detect the whole spectrum of large deletions as can be found in Progressive External Ophthalmoplegia and in the Kearns-Sayre syndrome. The advantage of this PCR-based test compared to Southern blot analysis is the sensitivity of the method for detecting deletions. In many cases patient’s leukocyte DNA is sufficient for making a diagnosis saving the patient a muscle biopsy procedure (Chapter 2). A single stranded conformation analysis (SSCP) screening method for mitochondrial tRNA mutations revealed in a patient with a mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS-pheno-type), a mutation in the tRNAVal gene (G1642A) being the second report of this mutation. Our observation was done independently and our patient’s phenotype is the same as in the former report confirming its likely pathogenicity. The phenotype of this patient differed from other MELAS patients because of the involvement of small cerebral arteries in the disease process. This involvement has not been reported before (Chapter 3). Next the analysis of five patients, with a biochemical phenotype of a complex III deficiency, for mutations in the only mitochondrially encoded subunit of complex III, the cytochrome b gene is described. In one patient a four base pair deletion-mutation at position 14787 and a homoplasmic SUMMARY 187 polymorphism are found. The mutation is heteroplasmic and present in 95% in muscle. In the clinically unaffected mother no mutation is detected. This frame shift mutation is predicted to cause a severe disruption of the synthesis of the cytochrome b protein. The phenotype of the patient, a Parkinsonism-MELAS overlap syndrome, has not been described before, neither in association with a complex III deficiency nor with a mutation in the cytochrome b gene. In two out of the four other patients the mutation analysis revealed two different homoplasmic polymorphisms (Chapter 4). In a patient with symptoms as seen in patients with a Leigh syndrome is a de novo arisen T8993C mitochondrial mutation reported. Hypotheses are formulated to explain this de novo event and the rise in mutant rate from 0% in the mother’s muscle mtDNA to 79% in the patient. Nuclear encoded, modifier genes are very likely necessary to understand the high percentage of heteroplasmy for this mutation (Chapter 5). Hereafter is the use of denaturing high performance liquid chromatography (DHPLC) technology demonstrated as an answer to the increasing number of different tests to exclude all the possible mtDNA mutations. The DHPLC method is a fast, reliable and sensitive method to detect heteroduplexes that result from heteroplasmic strands. Therefore this method is particularly suited for mtDNA screening, because most mutations in the mtDNA are heteroplasmic. A mtDNA-DHPLC protocol was developed that enables a complete mtDNA mutation analysis within one day. Levels of heteroplasmy as low as 0.5% for the A8344G mutation can be detected. The first six mitochondrial encephalomyopathy patients screened with this method showed a mutation in three out of six patients tested. Exclusion of mtDNA involvement supports a subsequent investigation of nuclear genes and has important implications for counselling (Chapter 6). There are only a few therapeutic possibilities for patients with mitochondrial encephalomyopathies. In case of a mtDNA mutation as the causative factor for disease also the possibilities for prenatal diagnosis are limited because of the complicated way the mutation is transmitted. For the first time a prenatal diagnosis and transmission findings are reported in a family with Leigh syndrome associated with the T9176C (ATPase6 gene) mutation (Chapter 7). In the second part of the thesis the characterization and mutation screening of the three flavoprotein fraction genes, the NDUFV1, NDUFV2, NDUFV3 genes, of the complex I are described. Using chaotropic agents 188 SUMMARY complex I can be divided in three fractions. One of the fractions, the flavoprotein fraction, consists of three subunits of 51, 24 and 10 kDa and is functionally important for complex I and the oxidative phosphorylation (Chapter 8-11). First the cloning and mapping of the gene coding for the smallest of the three subunits the NDUFV3 or 10 kDa-gene is described. The human cDNA sequence was elucidated by screening a human renal cDNA library with the known bovine 10-kDa cDNA. The 5' end of the cDNA was obtained with the rapid amplification of cDNA ends (RACE) procedure. Northern blot procedures showed the gene to be ubiquitously expressed. The gene contains three exons and spans about 20 kb. A Southern blot panel with human/hamster somatic cell hybrids showed that the gene is localized on chromosome 21. A 10 kDa gene containing cosmid was derived from a chromosome 21-specific cosmid library and used for a fluorescence in situ hybridization (Fish) procedure to refine the chromosome 21 location to 21q22.3 (Chapter 8). Next the cloning and characterization of the Fe-S cluster containing 24 kDa subunit gene is reported. The homologous bovine 24 kDa cDNA was used to screen a human cosmid library. The search was complicated by the presence of a pseudogene. The 24kDa cDNA cosmids were mapped by screening a Southern blot panel of human/hamster somatic cell hybrids to two different genes. One large fragment mapped to chromosome 19 and three smaller fragments to chromosome 18. Further refinement of the mapping was done with somatic cell hybrids containing either chromosome 18 or 19 fragments. With this procedure the locus could be assigned to 18p11.2-pter and to chromosome 19q13.3-qter. In a Fish procedure the loci were further refined to 18p11.2-11.31 and 19qter. The two genes were sequenced and revealed that the chromosome 19 locus represented a pseudogene and that the chromosome 18 locus represented the active 24 kDa gene. Northern blot analysis showed an ubiquitous gene expression (Chapter 9). Then the structure of the NDUFV1 gene, encoding the 51 kDa flavoprotein subunit of complex I, is described. The structure of the gene was clarified by using the known bovine 51 kDa cDNA sequence. With primers derived from the cDNA, PCR fragments from genomic DNA were generated. The gene appeared to contain 10 exons coding for 464 amino acids and spanned about 5 kb of the human genome. Northern blot analysis showed ubiquitous gene expression with the highest expression in pan- SUMMARY 189 creas. For testis mRNA a unique mRNA length fragment was present (Chapter 10). Following the characterisation of the three flavoprotein subunit genes NDUFV1, NDUFV2 and NDUFV3 the mutation analysis is described. For this comprehensive mutation analysis twenty patients with a mitochondrial encephalomyopathy and an isolated complex I deficiency were selected. No mutations in this group of patients were detected. Three polymorphisms were found in the NDUFV2 gene. This study supports the idea that the flavoprotein fraction of complex I is not a hotspot for mutations (Chapter 11). Finally the new findings presented in this thesis are put in perspective and directions for future research are discussed (Chapter 12).