Schematic representation of the TCRA locus and of SNPs associated with narcolepsy. The TCRA locus consists of clusters of V and J segments and exons of the C region. The T-Cell Receptor delta locus (TRD) resides within the TCRA locus. A 40kb region of LD encompasses half of the TRAJ segments and is flanked by TRAJ32 and the second exon of the TRAC gene. Within this region, 3 SNPs are highly associated with narcolepsy, separated by 3 and 15 kb successively. In Caucasians, the association is equivalent with rs12587781 and rs1154155 (Tables 1 and 2), and LD is extremely high (r²=0.97 and 0,94 n=1154 cases, n=1425 controls, correlations calculated using Haploview). In contrast, the association is stronger with rs1154155 than rs12587781 in Asians (Table 2), a phenomenon explained by the lower LD in this ethnic group (r²=0.62 and 0.52, n=553 cases, n=603 controls). Intermediate LD was seen in African-American individuals (r²=0.74 and 0.71, n=124 cases, n=142 controls). The association with rs1263646 is weaker across all ethnic groups, most notably Asians and African Americans (Table 2). These results, depicted as values for cases and controls combined in this figure, illustrate the value of trans-ethnic mapping.