The relative power of family-based and case-control designs for linkage disequilibrium studies of complex human diseases. II. Individual genotyping

In this paper we consider test statistics based on individual genotyping. F or sibships without parents, but with unaffected as well as affected sibs, we introduce a new test statistic (referred to as T-DS), which contrasts th e allele frequency in affected sibs versus that estimated for the parents f rom the entire sibship. For sibships without parents, this test is analogou s to the TDT and is completely robust to nonrandom mating patterns. The eff iciency of the T-DS test is comparable to that of the T-HS test [which comp ares affected vs, unaffected sibs and was based on DNA pooling), for sibshi ps with one affected child. However, as the number of affected sibs in the sibship grows, the relative efficiency of the T-DS test versus the T-HS tes t also increases. For example, for sibships with three affected, one-third fewer families are required; for families with four affected, nearly half a s many are required. Thus, when sibships contain multiple affected individu als, the T-DS test provides both an increase in power and robustness to non random mating.