To test the hypothesis that genetic factors are operative in the predisposition to leprosy (Hansen's disease) in humans, a genetic epidemiologic investigation was performed on 269 leprosy kindreds containing 552 affected individuals from an isolated population in Papua New Guinea. The community, and not the family, was the basic social unit. Leprosy, an infectious disease, was not communal but strongly familial within the Karimui. Segregation analysis, to determine whether a major gene for the susceptibility to leprosy was segregating within a single multi-generational kindred, could not differentiate between a Mendelian genetic and a purely environmental hypothesis. The composite kindred data, however, suggest a genetic hypothesis for the non-immunologically induced susceptibility to leprosy per se. Within familial kindreds leprosy invariably emanated from a common ancestral sibship, and risk was associated with the closeness of kin but not with infectivity or severity.
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