TK2 mutation presenting as indolent myopathy

Recessive mutations in the TK2 gene typically cause fatal infantile mitochondrial DNA (mtDNA) depletion syndromes (MDS).(1-3) However, the progression of weakness may vary,(4) as shown by recently described adult patients with late-onset myopathy.(5,6) To date, only 5 adult patients with TK2-related MDS have been reported. Herein, we describe a man who had several unusual features. Clinically, he was weak as a child but sought medical attention as an adult. At the molecular level, multiple mtDNA deletions in muscle were more prominent than mtDNA depletion.