Late-childhood-onset spinal muscular atrophy in three Melanesian families in Papua New guinea.

Late-childhood-onset spinal muscular atrophy (SMA) with rapid progression from proximal to distal muscle groups and leading to severe incapacity or death in adolescence or early adult life, was studied in two Melanesian families in Papua New Guinea. Probable SMA with cardiomyopathy was observed in a 12-year-old boy in a related family. The pattern of inheritance in the study group did not conform to any of the conventional Mendelian modes and it was conjectured that the disease was expressed in heterozygote carriers of the SMA gene only when an allelomorphic activator gene was present.