Background: Isobutyryl-CoA dehydrogenase (IBD) is a mitochondrial enzyme catalysing the third step in the degradation of the essential branched-chain amino acid valine and is encoded by ACAD8. ACAD8 mutations lead to isobutyryl-CoA dehydrogenase deficiency (IBDD), which is identified by increased C4-acylcarnitine levels. Affected individuals are either asymptomatic or display a variety of symptoms during infancy, including speech delay, cognitive impairment, failure to thrive, hypotonia, and emesis. Methods: Here, we review all previously published IBDD patients and describe a girl diagnosed with IBDD who was presenting with autism as the main disease feature. Results: To assess whether a phenotype-genotype correlation exists that could explain the development or absence of clinical symptoms in IBDD, we compared CADD scores, in silico mutation predictions, LoF tolerance scores and C4-acylcarnitine levels between symptomatic and asymptomatic individuals. Statistical analysis of these parameters did not establish significant differences amongst both groups. Conclusion: As in our proband, trio whole exome sequencing did not establish an alternative secondary genetic diagnosis for autism, and reported long-term follow-up of IBDD patients is limited, it is possible that autism spectrum disorders could be one of the disease-associated features. Further long-term follow-up is suggested in order to delineate the full clinical spectrum associated with IBDD.

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Molecular Genetics and Genomic Medicine
Department of Clinical Genetics

Eleftheriadou, M. (Maria), Medici- van den Herik, E. (Evita), Stuurman, K.E, van Bever, Y, Hellebrekers, D.M.E.I, van Slegtenhorst, M.A, … Barakat, T.S. (2021). Isobutyryl-CoA dehydrogenase deficiency associated with autism in a girl without an alternative genetic diagnosis by trio whole exome sequencing: A case report. Molecular Genetics and Genomic Medicine. doi:10.1002/mgg3.1595