Complex segregation analysis of the locus for beta-aminoisobutyric acid excretion (BAIB).

High excretion of BAIB is determined by an incompletely recessive gene jointly with other familial factors. The parameters estimated from a Japanese sample are: gene frequency = 0.6, displacement between homozygotes = 2.1 sigma, dominance = 0.2, and polygenic heritability = 0.1. Supplementary tests support this mixed model and (unlike classical analysis) give no evidence of segregation disturbance. Complexity of BAIB inheritance should be allowed for in population comparisons and linkage studies, which can be performed reliably under the mixed model.