A polymorphism in the gene encoding carnosinase (CNDP1) as a predictor of mortality and progression from nephropathy to end-stage renal disease in type 1 diabetes mellitus

AIMS/HYPOTHESIS: Homozygosity for a five leucine repeat (5L–5L) in the carnosinase gene (CNDP1) has been found to be cross-sectionally associated with a low frequency of diabetic nephropathy (DN), mainly in type 2 diabetes. We prospectively investigated in patients with type 1 diabetes whether: (1) 5L–5L is associated with mortality; (2) there is an interaction of 5L–5L with DN or sex for prediction of mortality; and (3) 5L–5L is associated with progression to end-stage renal disease (ESRD). METHODS: In this prospective study in white European patients with type 1 diabetes, individuals with DN were defined by persistent albuminuria ≥300 mg/24 h. Controls without nephropathy were defined by persistent (>15 years) normoalbuminuria <30 mg/24 h. Leucine repeats were assessed with a fluorescent DNA analysis system. Onset of ESRD was defined by need to start chronic dialysis or kidney transplantation. RESULTS: The study involved 916 patients with DN and 1,170 controls. During follow-up for 8.8 years, 107 patients (14%) with 5L–5L died compared with 182 patients (13.8%) with other genotypes (p = 0.99). There was no significant interaction of 5L–5L with DN for prediction of mortality (p = 0.57), but a trend towards interaction with sex (p = 0.08). In patients with DN, HR for ESRD in 5L–5L vs other genotypes was not constant over time, with increased risk for 5L–5L beyond 8 years of follow-up (p = 0.03). CONCLUSIONS/INTERPRETATION: CNDP1 polymorphism was not associated with mortality, and nor was there an interaction of this polymorphism with DN for prediction of mortality in patients with type 1 diabetes. CNDP1 polymorphism predicts progression to ESRD in patients with DN, but only late after baseline measurements. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00125-010-1863-0) contains supplementary material, which is available to authorised users.