Both Type I fiber predominance and Type I fiber atrophy have been reported in DM1 (9, 10, 32), so we also examined the expression of the genes encoding Type I (MYH7), IIA (MYH2), and IIX (MYH1) fibers in DM1 patient muscle compared with healthy control muscle. The gene discussed is MYH1; the disease is myotonic dystrophy type 1.