A potential vulnerability locus for schizophrenia on chromosome 6p24-22: evidence for genetic heterogeneity

Genetic dissection of complex traits: guidelines for interpreting and reporting linkage results

Genetic studies are under way for many complex traits, spurred by the recent feasibility of whole genome scans. Clear guidelines for the interpretation of linkage results are needed to avoid a flood of false positive claims. At the same time, an overly cautious approach runs the risk of causing true hints of linkage to be missed. We address this problem by proposing specific standards designed to maintain rigor while also promoting communication.

An international two-stage genome-wide search for schizophrenia susceptibility genes

Schizophrenia is thought to be a multifactorial disease with complex mode of inheritance. Using a two-stage strategy for another complex disorder, a number of putative IDDM-susceptibility genes have recently been mapped. We now report the results of a two-stage genome-wide search for genes conferring susceptibility to schizophrenia. In stage I, model-free linkage analyses of large pedigrees from Iceland, a geographical isolate, revealed 26 loci suggestive of linkage. In stage II, ten of these were followed-up in a second international collaborative study comprising families from Austria, Canada, Germany, Italy, Scotland, Sweden, Taiwan and the United States. Potential linkage findings of stage I on chromosomes 6p, 9 and 20 were observed again in the second sample. Furthermore, in a third sample from China, fine mapping of the 6p region by association studies also showed evidence for linkage or linkage disequilibrium. Combining our results with other recent findings revealed significant evidence for linkage to an area distal of the HLA region on chromosome 6p. However, in a fourth sample from Europe, the 6p fine mapping finding observed in the Chinese sample could not be replicated. Finally, evidence suggestive of locus heterogeneity and oligogenic transmission in schizophrenia was obtained.

Evaluation of a susceptibility gene for schizophrenia on chromosome 6p by multipoint affected sib-pair linkage analysis

The influence of genetic factors in schizophrenia has been convincingly demonstrated by family, twin and adoption studies, but the mode of transmission remains uncertain. The reported pattern of recurrence risks suggests a set of interacting loci. Based on prior evidence for linkage on chromosome 6p (K. Kendler, pers. comm.), we have scanned the short arm of chromosome 6 in 54 families for loci predisposing to schizophrenia, using 25 microsatellite markers spanning 60 centiMorgans (cM). Allele sharing identity by descent was examined in affected sib-pairs from these families, followed by multipoint sib-pair linkage analysis. Positive lod scores were obtained over a wide region (D6S470 to D6S271), with a maximum lod score of 2.2 occurring near D6S274, located in 6p22. However, we obtained a lod score of -2 at D6S296, the locus found by others to provide the greatest linkage evidence. At D6S274, we report a positive lod score as do Straub et al. (individually non-significant). A combined total lod of 3.6-4.0 suggests the possibility of a susceptibility locus in this region. However, methodological differences between our studies makes a firm conclusion difficult.