SELECTION OF HOMOGENEOUS POPULATIONS FOR GENETIC-STUDY - THE PORTUGALGENETICS OF PSYCHOSIS PROJECT

Molecular genetic studies of psychiatric disorders must face the possi bility that despite the significant contribution of genetic factors to the expression of syndromes like schizophrenia, these syndromes may b e a heterogeneous collection of genetic and non-genetic illnesses. The se illnesses may be etiologically distinct from each other and still s hare many clinical features in common. Linkage studies of families wit h multiple affected members tend to favor the selection of genetic for ms of a syndrome but can still represent a heterogeneous set of differ ent genetic illnesses. To limit the potential genetic heterogeneity of a study sample, we selected a population that was geographically isol ated and was historically relatively genetically homogeneous. We then assessed the relative level of homogeneity utilizing a surname analysi s of the population of the Azores, mainland Portugal, rural USA, and u rban USA. The average number of families with the same last name corre cted for population size in the Azores is 30.88, in Coimbra it is 21.4 2, compared to 1.13 in a rural American population and 0.38 in an urba n American population. The results of this analysis indicate that the Azores have the highest degree of homogeneity, and mainland Portugal h as a high degree of homogeneity. Am. J. Med. Genet. 74: 286-288, 1997. (C) 1997 Wiley-Liss, Inc.