VPS13D-based disease: Expansion of the clinical phenotype in two brothers and mutation diversity in the Turkish population

VPS13D is a recently described gene. Worldwide, only 15 families with 23 affected individuals have been reported with a VPS13D-based disease. Mutated VPS13D causes a complex phenotype with a hyperkinetic movement disorder and ataxia, especially in childhood onset disease. The clinical phenotype of the rare adult-onset cases consists of cerebellar ataxia and/or spastic paraplegia. Here, we report the extensive clinical, laboratory and genetic findings of two offspring from consanguineous parents, with ages of disease onset at 57 and 49 with VPS13D-based ataxia. Although conventional magnetic resonance imaging showed mild cerebellar and cerebral atrophy, diffusion tensor imaging, applied for the first time for VPS13D patients, revealed prominent atrophy in U fibers and cerebellopontine tracts. Whole exome sequencing analysis revealed a biallelic Ala4210Val mutation in the VPS13D, reported only once in the literature. Complementary screening of our in-house database consisting of 295 ataxia and hereditary spastic paraplegia patients revealed two further ataxia patients with novel VPS13D variants. Screening the control cohort for VPS13D variants revealed one asymptomatic individual carrying a novel VPS13D variant. In this study, the phenotypic spectrum of VPS13D-based disease is expanded with the description of pre-senile onset predominant ataxia. Further, with the additional novel mutations described, the report is expected to contribute to the understanding of the yet elusive phenotype-genotype correlations in the rare VPS13D-based movement disorder.