The transcript was present at highest levels in skeletal and cardiac muscle, with lower expression in other tissues. Mutation analysis was performed using DNA samples from 2 unrelated patients with Barth syndrome and from 11 unrelated patients with Emery-Dreifuss muscular dystrophy. No disease-associated mutations were detected in the coding region of the gene; however, Parrish et al. found a novel 190-bp insertion/deletion polymorphism in the 3-prime untranslated region. Translation of the long open reading frame found in the cDNA yielded a putative 302-amino acid protein with 37.6% identity to human DNase I.DNASE1L1 was predicted to contain a signal sequence at the amino terminus, a transmembrane domain near the carboxyl terminus, and a helix-loop-helix domain.