Whole-exome sequencing identifies rare compound heterozygous mutations in the MSTO1 gene associated with cerebellar ataxia and myopathy.

Human MSTO1 is involved in the regulation of mitochondrial distribution and morphology and its unregulated expression leads to mitochondrial disorder. Despite its significance for mitochondrial functions, human MSTO1 gene is rarely studied before 2017. As of late, MSTO1 mutations have been reported to cause clinical manifestations such as myopathy, cerebellar atrophy and ataxia, motor developmental delay, and pigmentary retinopathy. Here we have performed a whole-exome sequencing in a family which includes two brothers showing cerebellar atrophy and ataxia, intellectual disability, and myopathy. As a result, two mutations were identified. One of these mutations has been identified as a missense mutation, c.836G > A; p. (Arg279His) and a novel frameshift variant, c.1259delG; p. (Gly420ValfsTer2). So, the two brothers both had compound heterozygous mutations with a combination of protein-truncation mutation and missense mutation. These findings suggested an association of MSTO1 mutations with the early onset of symptoms and revealed the genotype-phenotype correlation between different mutation cases. In this case, the two brothers both have pes planus which is not reported in other cases. This might suggest that the novel mutation is responsible for dysmorphia. Thus, the recessive and novel MSTO1 mutations enriches genetic information on the pathogenicity of MSTO1 in humans.