Association of the Q121 Variant of ENPP1 Gene With Decreased Kidney Function Among Patients With Type 2 Diabetes

Received 18 March 2008; accepted 29 July 2008. published online 28 October 2008.

Background

Insulin resistance has a role in diabetic kidney complications. The K121Q (lysine to glutamine substitution at amino acid 121, encoded by single-nucleotide polymorphism rs1044498) variant of the ectonucleotide pyrophosphatase/phosphodiesterase gene (ENPP1) has been associated with insulin resistance and related vascular complications in patients with type 2 diabetes (T2D) in many, although not all, studies. This study investigated whether the ENPP1 Q121 variant modulates the risk of decreased glomerular filtration rate (GFR) in patients with T2D.

Study Design

Cross-sectional study.

Setting & Participants

2 diabetes units from Italy (in Gargano and Padua) and 1 from the United States (Boston, MA) recruited a total of 1,392 patients with T2D.

Predictor

The ENPP1 Q121 variant.

Measurements

Estimated GFR from serum creatinine, urinary albumin excretion, blood pressure, hemoglobin A1c, triglycerides, total cholesterol, and high-density lipoprotein cholesterol.

Outcomes

Decreased GFRs (ie, estimated GFR <60 mL/min/1.73 m2).

Results

In the Gargano and Boston populations, according to the dominant model of inheritance, Q121 carriers (ie, individual with either KQ or QQ alleles) had an increased risk of decreased GFR: odds ratios (ORs) of 1.69 (95% confidence interval [CI], 1.1 to 2.6) and 1.50 (95% CI, 1.0 to 2.2), respectively. In the Padua set, the association was in the same direction, but did not reach formal statistical significance (OR, 1.77; 95% CI, 0.7 to 4.5). When the 3 studies were pooled, Q121 carriers showed an increased risk of decreased GFR (OR, 1.58; 95% CI, 1.2 to 2.1; P = 0.002). Also, pooled mean differences in absolute GFRs were different across genotype groups, with Q121 carriers showing lower GFRs compared with KK individuals (P = 0.04).

Limitations

P values not approaching a genome-wide level of significance.

Conclusions

Our data suggest that patients with T2D carrying the ENPP1 Q121 variant are at increased risk of decreased GFR.

Index Words: Gene polymorphism, insulin resistance, vascular diabetic complications, PC-1

1 Unit of Endocrinology, Scientific Institute Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy

2 Joslin Diabetes Center, Boston, MA

3 Research Unit of Diabetes and Endocrine Diseases, Scientific Institute Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy

4 Chair of Metabolic Diseases, University of Padova, Padova, Italy

5 Department of Medical and Surgical Sciences, University of Padova, Padova, Italy

6 Department of Clinical Pharmacology and Epidemiology, Consorzio Mario Negri Sud, S Maria Imbaro, Italy

7 Unit of Diabetes, Ospedali Riuniti of Bergamo, Bergamo, Italy

8 CSS-Mendel Institute, Sapienza University, Rome, Italy

9 Department of Clinical Sciences, Sapienza University, Rome, Italy

Address correspondence to Salvatore De Cosmo, MD, Endocrinologia, Scientific Institute “Casa Sollievo della Sofferenza” V le Cappuccini 1, 71013 San Giovanni Rotondo (FG), Italy

Vincenzo Trischitta, MD, Istituto CSS-Mendel, V le R Margherita 261, 00198 Roma, Italy

Originally published online as doi:10.1053/j.ajkd.2008.07.040 on October 28, 2008.

PII: S0272-6386(08)01298-5

doi:10.1053/j.ajkd.2008.07.040

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