Clinical whole Exome Sequencing Reveals Novel Homozygous Missense Variant in the PMPCA Gene causing Autosomal Recessive Spinocerebellar Ataxia.

Background & objective: Autosomal recessive cerebellar ataxias (ARCA) are rare heterogenous neurodegenerative disorders characterized by degeneration of the cerebellum and spinal cord with an early onset before the age of 20 years. PMPCA (MIM: 613036), is a key enzyme in mitochondrial protein processing which is critical for cell survival and growth. Our objective was to investigate Peptidase, Mitochondrial Processing Subunit Alpha (PMPCA) mutations linked with Spinocerebellar ataxia, autosomal recessive 2 (SCAR2).

Method: In the current study, Whole Exome Sequencing (WES) was done followed by Sanger sequencing for the validation of the WES results.

Results: WES results identified a novel homozygous variant, NM_015160.2: c.802C>T p.(Arg268Trp) in PMPCA gene. Mutation in this gene leads to progressive cerebellar ataxia with fine motor skills difficulties, intentional tremors, slow slurred speech and learning difficulties in a 12-year-old Saudi patient. WES results were further validated by Sanger sequencing technique.

Conclusions: Identified phenotype in our case was similar as previously described for SCAR2 related conditions. To our knowledge, this is the first reported mutation in PMPCA gene leading to SCAR2 in Saudi Arabia. These findings will enrich the scarce literature, further provide a new insight on the role of PMPCA gene-related disorders leading to SCAR2 and expand the disease concept. In addition, this will help to establish a database for the disease and its causative factors will further help in controlling diseases resulting from consanguinity in Saudi population.