Subsequent linkage analyses of the large families provide additional evidence that GTS may be genetically heterogeneous. A heat map, shown in Figure 1, indicates the individual family Z scores on chromosome 2 for each of fifteen multigenerational families. Most of the families have positive linkage signals on chromosome 2p; however comparison across families indicates the absence of linkage in some families (Family 5, and likely Families 1 and 6). Furthermore, some families appear to have strong (Z score >3.719) linkage signals further along chromosome 2: Family 11 at D2S2216, Family 14 at D2S352 and D2S2368, and Family 15 at D2S2259. Thus, heterogeneity could partially explain the inconsistent results from previous linkage studies, as recently reviewed by Scharf and Pauls [60].
