Heritability estimates and evidence for linkage were obtained using the variance components approach implemented in SOLAR version 2.1.2 [7]. This method partitions the total phenotypic variance into variation due to a major QTL, polygenic background, and random error. Under the null hypothesis of no linkage, the QTL variance is fixed at zero and is tested against a polygenic model in which the same parameter is estimated from the data using maximum likelihood methods. Quantitative genetic analysis of lnmaxalc after adjustments for age, sex, and ethnicity (coded as white, black, other) yielded a residual kurtosis of 1.07. Non-normally distributed traits may lead to excess type I error and inflated LOD scores in the variance components model [8]. Therefore, robust LOD scores were calculated within SOLAR by applying a correction factor (0.86886) based on 11,000 simulations of a fully informative marker, unlinked to the trait [8]. Two-point and multipoint identity-by-descent (IBD) probabilities were calculated using SOLAR [7].
