Interactive effect of HLA and Gm tested in a study of 135 juvenile insulin-dependent diabetic families

Interaction between HLA and Gm for susceptibility to insulin-dependent diabetes (IDD) has been studied in 135 IDD families comparing HLA and Gm phenotype distributions in patients and sibling controls. The association analysis comparing the 135 index cases to 124 sibling controls did not show any significant interaction, but only a tendency for Gm 4,5 phenotypes to be more frequent in IDD patients, particularly in those who carried DR3/X. The sib pair analysis of 16 pairs of affected sibs did not show any distortion of segregation of Gm. On the other hand, among 98 sib pairs of one affected and one nonaffected sib, there was a significant distortion in favour of sib pairs with non-identical Gm phenotypes. However, no interaction between HLA and Gm was found. These results provide suggestive evidence that Gm or a locus very close to Gm could be involved in susceptibility to IDD.