DIABETES SUSCEPTIBILITY AT IDDM2 CANNOT BE POSITIVELY MAPPED TO THE VNTR LOCUS OF THE INSULIN GENE

An inconsistency has come to light between the conclusion of Lucassen et al. that IDDM2 (11p15.5) must lie within a 4.1 kilobase (kb) segmen t at the insulin (INS) locus and their own data showing statistically significant associations between insulin-dependent diabetes mellitus ( IDDM) and markers beyond the boundaries of that segment. We present da ta from an independent study of 201 IDDM patients and 107 non-diabetic control subjects that also show significant association with a marker 5' of the INS locus. Patients and control subjects were genotyped at INS/ + 1140 A/C (a surrogate for the variable number tandem repeat (VN TR) polymorphism in the regulatory part of the INS gene) and a marker 5' of the tyrosine hydroxylase (TH) gene, TH/pINS500-RsaI, making it 1 0 kb 5' of the VNTR. Homozygotes for INS/ + 1140 allele ' + ' were sig nificantly more frequent among IDDM patients than among control subjec ts (73 vs 45%, p < 0.001) giving an odds ratio of 3.3 (95% confidence interval (CI): 2.0-5.3). A very similar association was found for homo zygotes for the TH/RsaI allele ' + ' (53 vs 31%, p < 0.001) giving an odds ratio of 2.6 (95% CI 1.6-4.2). By multilocus analysis, the TH/Rsa I allele ' + ' identified a subset of INS/ + 1140 alleles ' + ' haplot ypes that are more specifically associated with IDDM (odds ratio = 5.4 , 95% CI 2.9-10.4) than allele + 1140 ' + ' as a whole. In conclusion, the segment of chromosome 11 that is associated with IDDM spans, at l east, the INS and TH loci. No legitimate claim can be made that IDDM2 corresponds to the VNTR polymorphism at the INS locus until the correc t boundaries for IDDM2 have been defined and other loci within them ha ve been excluded as determinants of IDDM.