Z-2 MICROSATELLITE ALLELE IS LINKED TO INCREASED EXPRESSION OF THE ALDOSE REDUCTASE GENE IN DIABETIC NEPHROPATHY

Epidemiological studies support the hypothesis that genetic factors mo dulate the risk for diabetic nephropathy (DN). Aldose reductase (ALDR1 ), the rate-limiting enzyme in the polyol pathway, is a potential cand idate gene. The present study explores the hypothesis that polymorphis ms of the (A-C)n dinucleotide repeat sequence, located 2.1 kb upstream of the transcription start site, modulate ALDR1 gene expression and t he risk for DN. We conducted studies at two different institutions, th e University of New Mexico Health Sciences Center (UNMHSC), and the Is tituto Scientifico H San Raffaele (HSR). There were four groups of vol unteers at UNMHSC: group I, normal subjects; group LT, patients with i nsulin-dependent diabetes mellitus (IDDM) without DN; group III, IDDM with DN; and group IV, nondiabetics with kidney disease. At HSR we stu died volunteers in groups I, II, and III. ALDR1 genotype was assessed by PCR and fluorescent sequencing of the (A-C)n repeat locus, and ALDR 1 messenger ribonucleic acid (mRNA) was measured by ribonuclease prote ction assay in peripheral blood mononuclear cells. At UNMHSC we identi fied 10 alleles ranging from Z-10 to Z+8. The prevalence of the Z-2 al lele among IDDM patients was increased in those with DN. Sixty percent of group III and 22% of group II were homozygous for Z-2. Moreover, 9 0% and 67% of groups III and II, respectively, had 1 or more copy of Z -2. In contrast, among nondiabetics, 19% of group IV and 3% of group I were homozygous for Z-2, and 69% and 32%, respectively, had 1 copy or more of Z-2. Among diabetics, homozygosity for the Z-2 allele was ass ociated with renal disease [odds ratio (OR), 5.25; 95% confidence inte rval, 1.71-17.98; P = 0.005]. ALDR1 mRNA levels were higher in patient s with DN (group III; 0.113 +/- 0.050) than in group I (0.068 +/- 0.02 5), group II (0.042 +/- 0.020), or group IV (0.015 +/- 0.011; P < 0.01 ). Among diabetics, ALDR1 mRNA levels were higher in Z-2 homozygotes ( 0.098 +/- 0.06) and Z-2 heterozygotes (0.080 +/- 0.04) than in patient s with no Z-2 allele (0.043 +/- 0.02; P < 0.05). In contrast, among no ndiabetics, ALDR1 mRNA levels in Z-2 homozygotes (0.034 +/- 0.04) and Z-2 heterozygotes (0.038 +/- 0.03) were similar to levels in patients without a Z-2 allele (0.047 +/- 0.03; P = NS). At HSR we identified ei ght alleles ranging from Z-12 to Z+2. The prevalence of the Z-2 allele was higher in group III than in group II. In group III, 43% of the pa tients were homozygous for Z-2, and 81% had one copy or more of the Z- 2 allele. In contrast, in group II, 4% were homozygous for Z-2, and 36 % had one copy or more of the Z-2 allele. IDDM patients homozygous for Z-2 had an increased risk for DN compared with those lacking the Z-2 allele (OR, 18; 95% confidence interval, 2-159). IDDM patients who had one copy or more of Z-2 had increased risk (OR, 7.5; 95% confidence i nterval, 1.9-29.4) for DN compared with those without the Z-2 allele. These results support our hypothesis that environmental-genetic intera ctions modulate the risk for DN. Specifically, the Z-2 allele, in the presence of diabetes and/or hyperglycemia, is associated with increase d ALDR1 expression. This interaction may explain the observed associat ion between the Z-2 allele and DN.