Pleiotropic effects of Chr15q25 nicotinic gene cluster and the relationship between smoking, cognition and ADHD.

Polymorphisms in the CHRNA5-CHRNA3-CHRNB4 gene cluster (Chr15q25) have been robustly associated with nicotine dependence, including genome-wide studies, as well as with cognitive and neuropsychological measures. In addition, cognitive processes can be influenced by nicotine use through nicotinic acetylcholine receptors (nAChRs). Here, we evaluated the effect of polymorphisms in CHRNA5-CHRNA3-CHRNB4 gene cluster and their interaction with tobacco smoking status on cognition in patients with Attention Deficit/Hyperactivity Disorder (ADHD). Eight SNPs from the CHRNA5-CHRNA3-CHRNB4 gene cluster were evaluated on a clinical sample of 403 adults with ADHD. Cognitive performance was assessed using the Wechsler Adult Intelligence Scale-Revised (WAIS-R). Analyses of covariance were used to assess the influence of single markers and their interaction with smoking status in the Vocabulary and Block Design subtests of WAIS-R. Correction for multiple comparisons was applied. Lifetime smoking was associated to Vocabulary subtest. The TT genotypes of CHRNA5 SNPs rs588765 and rs514743 showed a trend towards association with, respectively, higher and lower scores on the Vocabulary subtest. There was a significant interaction between intergenic SNP rs8023462 and smoking on Vocabulary scores. Our results are consistent with an influence of variants in the CHRNA5-CHRNA3-CHRNB4 gene cluster on cognitive measures. The overall scenario suggests a pleiotropic role of Chr15q25 nicotinic gene cluster with complex influences in ADHD, tobacco smoking and cognitive performance, characteristics that can be partially interdependent and may share underlying genetic factors.

The -308G>a polymorphism of the TNF gene is associated with proliferative diabetic retinopathy in Caucasian Brazilians with type 2 diabetes.

PURPOSE: We tested the hypothesis that tumor necrosis factor (TNF) gene polymorphisms are associated with diabetic retinopathy (DR) in Caucasians with type 2 diabetes mellitus. METHODS: In a case-control study, the -238G>A (rs361525), -308G>A (rs1800629), and -857C>T (rs1799724) polymorphisms of the TNF gene were genotyped in 745 outpatients with type 2 diabetes, including 331 subjects without DR, 246 with nonproliferative DR (NPDR), and 168 with proliferative DR (PDR). RESULTS: Genotype and allele frequencies of the -238G>A, -308G>A, and -857C>T polymorphisms in subjects with NPDR were not significantly different from those of subjects without DR (P > 0.05 for all comparisons). However, the A allele of the -308G>A polymorphism was more frequent in subjects with PDR than in those with no DR (18.1% vs. 11.5%, corrected P = 0.035). Multivariate logistic regression analysis showed that the -308A allele was independently associated with an increased risk of PDR, under a dominant model (adjusted odds ratio [aOR], 1.82; 95% confidence interval [CI], 1.11-2.98). The combined analysis of the three polymorphisms also showed that haplotypes containing the -308A allele were associated with an increased risk of PDR (aOR, 2.36; 95% CI, 1.29-4.32). CONCLUSIONS: This study detected, for the first time to our knowledge, an independent association of the -308G>A polymorphism in the TNF gene with PDR in Caucasian Brazilians with type 2 diabetes. This finding suggests that TNF is a potential susceptibility gene for PDR.

ADHD diagnosis may influence the association between polymorphisms in nicotinic acetylcholine receptor genes and tobacco smoking.

Polymorphisms in the CHRNA5-CHRNA3-CHRNB4 gene cluster have been shown to be involved in tobacco smoking susceptibility. Considering that attention deficit/hyperactivity disorder (ADHD) not only increases the risk but may also influence the molecular mechanisms of tobacco smoking, we analyzed the association between polymorphisms in the nicotinic acetylcholine receptor genes and tobacco smoking among individuals with or without ADHD. The sample included 1,118 subjects divided into four groups according to smoking status and ADHD diagnosis. Our results demonstrate that the minor alleles of two polymorphisms (rs578776 and rs3743078) in the CHRNA3 gene are associated with an increased risk of tobacco smoking only among patients with ADHD. These alleles have been shown in previous studies to be protective factors for smoking in subjects without ADHD. These findings add to existing evidence that ADHD may exert an important modifying effect on the genetic risk of smoking and should be considered in tobacco smoking association studies.

MR and GR functional SNPs may modulate tobacco smoking susceptibility.

A number of studies have demonstrated that stress is involved in all aspects of smoking behavior, including initiation, maintenance and relapse. The mineralocorticoid (MR) and glucocorticoid (GR) receptors are expressed in several brain areas and play a key role in negative feedback of the hypothalamic-pituitary-adrenal (HPA) axis. As nicotine increases the activation of the HPA axis, we wondered if functional SNPs (single nucleotide polymorphisms) in MR and GR coding genes (NR3C2 rs5522 and NR3C1 rs6198, respectively) may be involved in smoking susceptibility. The sample included 627 volunteers, of which 514 were never-smokers and 113 lifetime smokers. We report an interaction effect between rs5522 and rs6198 SNPs. The odds ratio (OR) for the presence of the NR3C2 rs5522 Val allele in NR3C1 rs6198 G carriers was 0.18 (P = 0.007), while in rs6198 G noncarriers the OR was 1.83 (P = 0.027). We also found main effects of the NR3C1 rs6198 G allele on number of cigarettes smoked per day (P = 0.027) and in total score of the Fagerström Test for Nicotine Dependence (P = 0.007). These findings are consistent with a possible link between NR3C2 and NR3C1 polymorphisms and smoking behavior and provide a first partial replication for a nominally significant GWAS finding between NR3C2 and tobacco smoking.