The discipline of genetic epidemiology pertains to the vertical transmission of the susceptibility (predisposition) to a complex disease in a structured population. This statement meets halfway 1 the broad definitiongiven by N. E. Morton and S. c. Chung in 1978 2 and the concise one given by M. -C. King et al. in 1984. 1t pinpoints the fundamental genetic hypothesis, namely, the existence of an inherited condition that predisposes an individual to a specific disease, and the corresponding subject ofinvestigation, the family. Thus, the genetic epidemiological situation consists of three basic...