title: A functional variant of the dimethylarginine dimethylaminohydrolase-2 gene is associated with insulin sensitivity.
abstract: BACKGROUND
  Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of endothelial nitric oxide synthase, which was associated with insulin resistance. Dimethylarginine dimethylaminohydrolase (DDAH) is the major determinant of plasma ADMA. Examining data from the DIAGRAM+ (Diabetes Genetics Replication And Meta-analysis), we identified a variant (rs9267551) in the DDAH2 gene nominally associated with type 2 diabetes (P = 3 × 10(-5)).
  
  
  RESULTS
  initially, we assessed the functional impact of rs9267551 in human endothelial cells (HUVECs), observing that the G allele had a lower transcriptional activity resulting in reduced expression of DDAH2 and decreased NO production in primary HUVECs naturally carrying it. We then proceeded to investigate whether this variant is associated with insulin sensitivity in vivo. To this end, two cohorts of nondiabetic subjects of European ancestry were studied. In sample 1 (n = 958) insulin sensitivity was determined by the insulin sensitivity index (ISI), while in sample 2 (n = 527) it was measured with a euglycemic-hyperinsulinemic clamp. In sample 1, carriers of the GG genotype had lower ISI than carriers of the C allele (67 ± 33 vs.79 ± 44; P = 0.003 after adjusting for age, gender, and BMI). ADMA levels were higher in subjects carrying the GG genotype than in carriers of the C allele (0.68 ± 0.14 vs. 0.57 ± 0.14 µmol/l; P = 0.04). In sample 2, glucose disposal was lower in GG carriers as compared with C carriers (9.3 ± 4.1 vs. 11.0 ± 4.2 mg × Kg(-1) free fat mass × min(-1); P = 0.009).
  
  
  CONCLUSIONS
  A functional polymorphism of the DDAH2 gene may confer increased risk for type 2 diabetes by affecting insulin sensitivity throughout increased ADMA levels.
authors.affiliation: Department of Medical and Surgical Sciences, University Magna Græcia of Catanzaro, Catanzaro, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Andreozzi
authors.forename: Ivan
authors.initials: I
authors.lastname: Presta
authors.forename: Gaia Chiara
authors.initials: GC
authors.lastname: Mannino
authors.forename: Daniela
authors.initials: D
authors.lastname: Scarpelli
authors.forename: Sara
authors.initials: S
authors.lastname: Di Silvestre
authors.forename: Natalia
authors.initials: N
authors.lastname: Di Pietro
authors.forename: Elena
authors.initials: E
authors.lastname: Succurro
authors.forename: Angela
authors.initials: A
authors.lastname: Sciacqua
authors.forename: Assunta
authors.initials: A
authors.lastname: Pandolfi
authors.forename: Agostino
authors.initials: A
authors.lastname: Consoli
authors.forename: Marta Letizia
authors.initials: ML
authors.lastname: Hribal
authors.forename: Francesco
authors.initials: F
authors.lastname: Perticone
authors.forename: Giorgio
authors.initials: G
authors.lastname: Sesti
mesh_terms: D000581:Amidohydrolases / Q000235:genetics*; D003924:Diabetes Mellitus, Type 2 / Q000201:enzymology / Q000235:genetics; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D020022:Genetic Predisposition to Disease / Q000235:genetics; D061307:Human Umbilical Vein Endothelial Cells / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D019001:Nitric Oxide Synthase / Q000378:metabolism; D011110:Polymorphism, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D019001:Nitric Oxide Synthase; D000581:Amidohydrolases; C059999:dimethylargininase