A neuromuscular disorder characterized by weakness, arthrogryposis, kyphoscoliosis, short stature, cleft palate, ptosis and susceptibility to malignant hyperthermia during anesthesia. Reported exclusively in Native American Indians (Lumbee Indian population of North Carolina). Within this population, the prevalence is estimated at approximately 1:5,000. The locus has been localized to 12q13.13-14.1. The disease is transmitted in an autosomal recessive manner.