Diabetes, Vol 46, Issue 10 1637-1642, Copyright © 1997 by American Diabetes Association
Evidence for association between the class I subset of the insulin gene minisatellite (IDDM2 locus) and IDDM in the Japanese population
T Awata, S Kurihara, C Kikuchi, S Takei, I Inoue, C Ishii, K Takahashi, K Negishi, Y Yoshida, R Hagura, Y Kanazawa and S Katayama
Fourth Department of Internal Medicine, Saitama Medical School, Japan. awata@saitama-med.ac.jp
Although the shortest (class I) minisatellite (i.e., variable number of
tandem repeats [VNTR]) alleles in the 5' region of the insulin gene are
positively associated with IDDM in Caucasians, the majority of Japanese are
homozygous for class I alleles. Here, we determined the exact length, in
number of repeat units (RUs), of class I alleles in Japanese subjects. The
distribution of class I alleles in Japanese was trimodal, with peaks
located at 32/33, 41, and 44 RUs. The shortest component (i.e., 1S [25-38
RUs]) alleles were significantly increased in the IDDM group compared with
the control group (54 vs. 46%; P = 0.040). The 1S/1S genotype was
significantly increased in the IDDM patients (34 vs. 20%; P = 0.005;
relative risk 2.1). Furthermore, the transmission disequilibrium test of
Japanese families with 1S/1M or 1S/1L heterozygous parents confirmed the
association of 1S alleles; 17 alleles of 1S and 6 alleles of 1M (39-41 RUs)
or 1L (42-44 RUs) were transmitted to affected offspring (P = 0.022). In
addition, we found tight linkage of 1S with allele 9 of the tyrosine
hydroxylase gene microsatellite and allele (-) of the IGF-II gene Apa I
polymorphism, but neither 9 nor (-) alleles were significantly associated
with IDDM. The present study suggests that a class I subset may have a role
in IDDM susceptibility in Japan. It was revealed that the difference
between 1S alleles and 1M or 1L alleles is almost consistently
characterized by a sequence variation generated by deletion of two copies
of an ACAGGGGTCC CGGGG repeat element, implying that sequence variation of
class I alleles may influence disease susceptibility.