Genetic epidemiological study of schizophrenia in Palau, Micronesia: Prevalence and familiality

We are studying the genetic etiology of schizophrenia in the Republic of Pa lau, a remote island nation in Micronesia that has been geographically and ethnically isolated for approximately 2,000 years. The first epidemiologica l phase sought to estimate the lifetime prevalence of schizophrenia and eva luate the familiality of the illness based on complete ascertainment of cas es and families segregating schizophrenia, A total of 160 strictly defined cases of schizophrenia were ascertained in a population of 13,750 adults wh o were 15 years of age and older. The lifetime prevalence of strictly defin ed schizophrenia in Palau was 1.99% overall and 2.77% in males vs. 1.24% in females. This greater than 2:1 male-to-female risk ratio for schizophrenia was accompanied by an earlier mean age of onset for males (23.3 years) tha n for females (27.5 years). These 160 cases of strict schizophrenia represe nt 59 separate families each identified by a single common founder. Eleven of these families have 5 to 14 cases and represent nearly half of the stric t schizophrenia cases in Palau, Although schizophrenia is clearly aggregati ng in these 11 families, cases are distributed sparsely throughout the larg e sibships, In the entire sample of 160 cases of strict schizophrenia, ther e were only 11 sib-pairs and 2 sib-trios, When a family was defined to incl ude third-degree relatives, only 11 cases (6.9%) were nonfamilial, The majo rity of the ascertained cases can be linked together into extended pedigree s with complex multilineal inheritance patterns. These intricately intercon nected families may pose challenges for traditional linkage techniques. How ever, these Palauan families represent a valuable resource for studying the genetic etiology of schizophrenia because there may be fewer susceptibilit y genes for schizophrenia in this genetic isolate than in the heterogeneous populations that are common throughout the world today. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:4-10, 1999. (C) 1999 Wiley-Liss, Inc.