Family-Based Association Tests (FBAT, Rabinowitz and Laird 2000) were employed for genetic association analyses. Family-based association designs test for linkage as well as association, and avoid spurious associations caused by admixture of populations. They are appropriate in family samples such as this study. FBAT builds on the original transmission disequilibrium test (TDT) method (Spielman and Ewens 1996) in which alleles transmitted to affected offspring are compared with the expected distribution of alleles among offspring. It compares the genotype distribution observed in the ‘cases’ to its expected distribution under the null hypothesis: in this case, given the previous positive finding of linkage (LOD=3.5) in the same region (Jones and others 2006; Jones and others 2004) the null hypothesis tested was “no association, in the presence of linkage”.
