Isolated distal myopathy of the upper limbs associated with mitochondrial DNA depletion and polymerase gamma mutations.

Objective: To describe an unusual clinical phenotype in an adult harboring 2 compound heterozygous polymerase γ (POLG) mutations.

Design: Case report.

Setting: University-based outpatient neurology clinic and pathology and genetics laboratory.

Patient: A 27-year-old man presenting with isolated distal myopathy of the upper extremities in the absence of sensory disturbances.

Results: Histochemical analysis of a muscle biopsy specimen showed numerous cytochrome c oxidase-deficient fibers. Molecular analysis revealed marked depletion of muscle mitochondrial DNA in the absence of multiple mitochondrial DNA deletions. Sequence analysis of the POLG gene revealed heterozygous sequence variants in compound c.1156C>T (p.R386C) and c.2794C>T (p.H932Y) segregating with clinical disease in the family. The p.R386C change appears to be a novel mutation.

Conclusion: Our case broadens the phenotypic spectrum of disorders associated with POLG mutations and highlights the complex relationship between genotype and phenotype in POLG-related disease.