We speculated previously that these genes could be functionally related. Within this gene cluster, a haplotype spanning TTC12 and ANKK1 was strongly associated with ND in European- and African-American (EA and AA, respectively) family samples (Gelernter et al., 2006). Haplotypes around TTC12 exon 3, NCAM1 exon 12, and exons 2 and 5 of ANKK1 were also associated with AD in two other independent EA samples, one population-based and one family-based (Yang et al., 2007). These associations were not attributable to linkage disequilibrium (LD) with DRD2 and DRD2 itself showed only very limited association. Among these identified susceptibility regions, the association signals from TTC12 were consistently prominent. The present study considers the latter samples (i.e., from Yang et al, 2007) in the context of additional diagnostic information, with the goal of adding to our understanding of the nature of the associated phenotypes.
