Results from segregation analyses of family studies have been consistent with the hypothesis that GTS is genetically transmitted [7, 8, 26, 41–49]. The majority of these studies support the hypothesis of at least one genetic locus with major effect, though in retrospect each indicate the likelihood of many additional genetic loci and/or the presence of genetic heterogeneity [7, 8, 26, 42, 44, 46–49]. Several investigators have observed bilineal transmission [27, 50–52] in a number of GTS and CT families, raising the possibility of nonrandom selection of partners for marriage (assortative mating). This fact further complicates the interpretation of segregation analyses, since the majority of these studies were performed under the assumption of random mating.
