Bethlem myopathy-1 (BTHLM1) is a congenital muscular dystrophy characterized by distal joint laxity and a combination of distal and proximal joint contractures. Weakness usually begins in mid-childhood or adolescence, but progression is slow and ambulation is usually retained into adulthood (summary by Butterfield et al., 2013). For a discussion of genetic heterogeneity of Bethlem myopathy, see BTHLM1A (158810). [from OMIM]