Comparative analysis with fibroblasts from a previously reported case with <i>MSTO1</i> mutation revealed notable differences in the severity of mitochondrial dysfunction, suggesting potential genotype-phenotype correlations.<h4>Conclusion</h4>Our findings provide evidence linking the novel MSTO1 variants c.756A>G and c.1339G>A to mitochondrial dysfunction and broaden the phenotypic spectrum of MSTO1-related mitochondrial disorders to encompass a milder, adult-onset form of cerebellar ataxia. Here, MSTO1 is linked to aceruloplasminemia.