ISCA2 mutation causes infantile neurodegenerative mitochondrial disorder

Background There are numerous nuclear genesthat cause mitochondrial disorders and clinically and genetically heterogeneous disorderswhose aetiology often remains unsolved. In this study, we aim to investigate an autosomal recessive syndrome causing leukodystrophyand neuroregression. We studied six patients from five unrelated consanguineousfamilies. Methods Patients underwent full neurological, radiological, genetic, metabolic and dysmorphological examinations. Exome sequencingcoupled with autozygosity mapping, Sanger sequencing, microsatellite haplotyping, standard and molecular karyotyping and whole mitochondrial DNA sequencing were used to identify the genetic cause of the syndrome. Immunohistochemistry, transmission electron microscopy, confocal microscopy, dipstickassays, quantitative PCR, reverse transcription PCR and quantitative reverse transcription PCR were performed on different tissue samples from the patients. Results We identified a homoallelic missense founder mutationin ISCA2 leading to mitochondrial depletion and reduced complex I activity as well as decreased ISCA2 , ISCA1 and IBA57 expression in fibroblasts. MRI indicated similar white matter abnormalities in the patients. Histological examination of the skeletal muscle showed mild to moderate variation in myofibre size and the presence of many randomly distributed atrophic fibres. Conclusions Our data demonstrate that ISCA2 deficiency leads to a hereditary mitochondrial neurodegenerative white matter disease in infancy.