Mutations in <i>MSTO1</i> are linked to a rare mitochondrial disorder characterized by early-onset myopathy and cerebellar ataxia, with 31 cases reported globally to date, which underscores its exceptional rarity.<h4>Methods</h4>We conducted comprehensive clinical, molecular, and biochemical investigations in a patient harboring novel <i>MSTO1</i> variants.<h4>Results</h4>We identified a patient presenting with adult-onset progressive ataxia and cerebellar atrophy who carried two novel compound heterozygous variants in the <i>MSTO1</i> gene (c.756A>G, p.Glu252Glu; c.1339G>A, p.Glu447Lys). The gene discussed is MSTO1; the disease is myopathy.