Background: Ataxia with oculomotor apraxia type 1 is an autosomal-recessive neurodegenerative disorder characterized by a childhood onset of slowly progressive cerebellar ataxia, followed by oculomotor apraxia and a severe primary motor peripheral axonal motor neuropathy. Ataxia with oculomotor apraxia type 1 is caused by bi-allelic mutations in APTX (chromosome 9p21.1). Case presentation: Our patient has a clinical presentation that is typical for ataxia with oculomotor apraxia type 1 with no particularly severe phenotype. Multiplex Ligation-dependent Probe Amplification analysis resulted in the identification of a homozygous deletion of all coding APTX exons (3 to 9). SNP array analysis using the Illumina Infinium CytoSNP-850 K microarray indicated that the deletion was about 62 kb. Based on the SNP array results, the breakpoints were found using direct sequence analysis: c.-5 + 1225_*44991del67512, p.0?. Both parents were heterozygous for the deletion. Homozygous complete APTX deletions have been described in literature for two other patients. We obtained a sample from one of these two patients and characterized the deletion (156 kb) as c.-23729_*115366del155489, p.0?, including the non-coding exons 1A and 2 of APTX. The more severe phenotype reported for this patient is not observed in our patient. It remains unclear whether the larger size of the deletion (156 kb vs 62 kb) plays a role in the phenotype (no extra genes are deleted). Conclusion: Here we described an ataxia with oculomotor apraxia type 1 patient who has a homozygous deletion of the complete coding region of APTX. In contrast to the patient with the large deletion, our patient does not have a severe phenotype. More patients with deletions of APTX are required to investigate a genotype-phenotype effect.

APTX, Ataxia with oculomotor apraxia type 1, Breakpoint mapping, Deletion, Genetic testing, Homozygous, MLPA, SNP array analysis
dx.doi.org/10.1186/s12881-015-0213-y, hdl.handle.net/1765/86082
B M C Medical Genetics
Department of Clinical Genetics

van Minkelen, R, Guitart, M, Escofet, C, Yoon, G, Elfferich, P.C, Bolman, G.M, … van den Ouweland, A.M.W. (2015). Complete APTX deletion in a patient with ataxia with oculomotor apraxia type 1. B M C Medical Genetics, 16(1). doi:10.1186/s12881-015-0213-y