Fine mapping of AHI1 as a schizophrenia susceptibility gene: from association to evolutionary evidence.

In previous studies, we identified a locus for schizophrenia on 6q23.3 and proposed the Abelson helper integration site 1 (AHI1) as the candidate gene. AHI1 is expressed in the brain and plays a key role in neurodevelopment, is involved in Joubert syndrome, and has been recently associated with autism. The neurodevelopmental role of AHI1 fits with etiological hypotheses of schizophrenia. To definitively confirm our hypothesis, we searched for associations using a dense map of the region. Our strongest findings lay within the AHI1 gene: single-nucleotide polymorphisms rs11154801 and rs7759971 showed significant associations (P=6.23E-06; P=0.84E-06) and haplotypes gave P values in the 10E-8 to 10E-10 range. The second highest significant region maps close to AHI1 and includes the intergenic region between BC040979 and PDE7B (rs2038549 at P=9.70E-06 and rs1475069 at P=6.97E-06), and PDE7B and MAP7. Using a sample of Palestinian Arab families to confirm these findings, we found isolated signals. While these results did not retain their significance after correction for multiple testing, the joint analysis across the 2 samples supports the role of AHI1, despite the presence of heterogeneity. Given the hypothesis of positive selection of schizophrenia genes, we resequenced a 11 kb region within AHI1 in ethnically defined populations and found evidence for a selective sweep. Network analysis indicates 2 haplotype clades, with schizophrenia-susceptibility haplotypes clustering within the major clade. In conclusion, our data support the role of AHI1 as a susceptibility gene for schizophrenia and confirm it has been subjected to positive selection, also shedding light on new possible candidate genes, MAP7 and PDE7B.

Gly460Trp alpha-adducin gene polymorphism and endothelial function in untreated hypertensive patients.

OBJECTIVES: Endothelium-dependent vasodilatation is impaired in essential hypertension. Besides traditional and emerging cardiovascular risk factors, genetic factors may also promote deleterious alterations of endothelial physiology. The aim of the present study was to investigate the relationship between the 460Trp allele of ADD1 and endothelium-dependent vasodilation in 110 never-treated hypertensive patients. METHODS: Forearm blood flow (FBF) was measured during intra-arterial infusion of acetylcholine (ACh) and sodium nitroprusside (SNP) at increasing doses. Analysis of endothelium-dependent and endothelium-independent vasodilation was tested according to ADD1 genotype. RESULTS: The FBF values at the three incremental doses of ACh were 5.22 +/- 0.24 (+76%), 8.64 +/- 0.45 (+193%) and 14.74 +/- 0.71 (+395%) ml/100 ml of tissue per min for Gly460Gly and 4.63 +/- 0.20 (+51%), 6.84 +/- 0.36 (+123%) and 11.22 +/- 3.8 (+269%) ml/100 ml of tissue per min for 460Trp. Thus, ACh-stimulated FBF was significantly reduced in hypertensive subjects carrying the 460Trp allele of ADD1 (P < 0.001). SNP-stimulated FBF was not affected by ADD1. CONCLUSIONS: The main finding in this study was that in essential hypertensives the 460Trp allele of ADD1 is strongly associated with an impaired endothelium-dependent vasodilation, a powerful predictor of cardiovascular risk.

Common genetic variants and haplotypes in renal CLCNKA gene are associated to salt-sensitive hypertension.

Abnormal renal reabsorption of sodium (Na(+)) is likely to play a role in the pathogenesis of salt-sensitivity. In the kidney, chloride channels CLC-Ka (gene CLCNKA) and CLC-Kb (gene CLCNKB) and their subunit Barttin (gene BSND) have important effects on the control of Na(+) and water homeostasis. We investigated if single nucleotide polymorphisms (SNPs) or haplotypes within CLCNKA, CLCNKB and BSND loci affect salt-sensitivity in hypertensive subjects. Associations between blood pressure (BP) change after Na(+)-load and 15 SNPs spanning the length of CLCNKA and CLCNKB and six SNPs spanning the length of BSND were studied in 314 never treated essential hypertensives who underwent an i.v. infusion of saline (300 mm NaCl in 2 l H(2)O in 120 min). Four SNPs were significantly associated with BP change after Na-load. Rs848307 (P = 0.0026) and rs1739843 (P = 0.0023) map upstream the 5' of CLCNKA. Non-coding Rs1010069 (P = 0.0006) and non-synonymous rs1805152 (Thr447Ala; P = 0.0078) map within CLCNKA. Moreover, basal plasma renin activity and heart rate (measured before Na-load) were significantly lower in patients carrying the alleles associated with the larger mean BP increase after Na-load, indicating that such alleles are associated with chronic volume expansion. This study supports the candidacy of CLCNKA as a new susceptibility gene for salt-sensitivity.

Alpha-adducin and angiotensin-converting enzyme polymorphisms in hypertension: evidence for a joint influence on albuminuria.

BACKGROUND: A single-nucleotide polymorphism (Gly460Trp) within the alpha-adducin gene (ADD1) may influence several renal phenotypes, including salt sensitivity, susceptibility to renal failure, the renal haemodynamics and confer a worse cardiovascular risks profile. However, its relationship with microalbuminuria, a marker of early renal and cardiovascular damage and an independent predictor of morbid events in hypertension, is unknown. For this reason, we related the ADD1 genetic polymorphism to urine albumin levels and other clinical variables in essential hypertensive men. The angiotensin-converting enzyme (ACE) insertion/deletion (ID) polymorphism was also evaluated because of its interactive potential with the ADD1 genotype. METHODS: Albuminuria (three overnight collections), echocardiographic left ventricular mass index, blood pressure, body mass index, renal function, glucose and lipids were measured in 238 genetically unrelated, never treated, uncomplicated Caucasian essential hypertensive men. Polymerase chain reaction or a 5' nuclease assay were used to characterize the ACE ID and ADD1 Gly460Trp variants, respectively. RESULTS: Microalbuminuria (albuminuria >or= 15 microg/min) was more frequent in patients with the ACE DD variant, but only in those with a ADD1 Gly460Gly background. In contrast, urine albumin did not differ by ACE ID genotype in the presence of mutated ADD1 Trp alleles. ADD1 polymorphisms per se were not associated with albuminuria. Cardiovascular, renal, metabolic parameters were homogeneously distributed among different genetic backgrounds. CONCLUSIONS: ACE DD and ADD1 Gly460Gly polymorphisms may jointly influence albuminuria in hypertensive men, 460Gly homozygosis facilitating or, possibly, the 460Trp allele mitigating the noxious renal impact of the ACE DD genotype. The data highlight further the complex pathophysiological implications of microalbuminuria in hypertension.

The 460Trp allele of alpha-adducin increases carotid intima-media thickness in young adult males.

BACKGROUND: The 460Trp allele of the alpha-adducin gene (ADD1), which is involved in a form of salt-sensitive hypertension, has been associated with patterns of target organ damage. OBJECTIVES: As carotid artery intima-media thickness (IMT) largely depends upon unknown genetic factors, besides being associated to conventional risk factors, we tested the association of the 460Trp allele of ADD1 with IMT in a well-characterized sample of young healthy normotensive subjects, to assess the role of ADD1 polymorphism without overlapping effects of age or already elevated blood pressure. METHODS: Anthropometric measurements, blood pressure (BP), and carotid artery wall IMT (high-resolution sonography and digitalized morphometry) were obtained in 420 healthy normotensive Caucasian university students. Genotypes for ADD1 were detected by automated genomic polymerase chain reaction (PCR). RESULTS: ADD1 genotypes were evenly distributed between genders. IMT was significantly larger in carriers of the 460Trp allele of ADD1, while a significant gender x ADD1 interaction (P = 0.02) demonstrated that IMT was increased only in males carrying the 460Trp allele (P < 0.001). No significant association was found in females. CONCLUSIONS: The 460Trp allele of ADD1 contributes substantially to increase carotid IMT, in a male hormonal milieu only, at least in the young age range.

GH replacement therapy increases plasma osteoprotegerin levels in GH-deficient adults.

OBJECTIVE: Osteoprotegerin (OPG), a glycoprotein belonging to the tumor necrosis factor receptor family, is an endogenous inhibitor of osteoclastogenesis produced by cells of the osteoblast lineage. OPG is a key cytokine involved in the regulation of osteoblast/osteoclast cross-talk. Since GH replacement therapy in GH deficiency (GHD) activates bone remodeling and increases bone mass, we investigated if short-term GH replacement therapy affects plasma OPG levels. DESIGN AND METHODS: Eighteen adults with GHD, ranging from 17 to 51 Years (nine childhood-onset and nine adult-onset) were enrolled in the study. All subjects were on stable replacement therapy, especially sex hormones. The starting dose of GH replacement therapy was 4 microg/kg per day x 7 days/week, and was progressively increased according to the serum IGF-I values. Biochemical parameters of bone and mineral metabolism were measured before and after 6 Months of GH replacement therapy. Bone mass density (BMD) was monitored at three skeletal sites (lumbar vertebrae, femur, radius) by dual-energy X-ray absorptiometry. RESULTS: After 6 Months of therapy, ionized calcium, parathyroid hormone and 25-OH vitamin D did not change, whereas total serum calcium and urinary calcium excretion increased significantly (P<0.01). Also osteocalcin and urinary deoxypyridinoline/24 h increased significantly (P<0.02, P<0.05 respectively). Mean basal T-scores of BMD values showed an osteopenic state, which remained unchanged after GH therapy. Plasma OPG increased significantly after 6 Months of therapy (P<0.02) and this increase was significantly correlated with the increase of osteocalcin (r=-0.52; P=0.04) and deoxypyridinoline values (r=-0.64; P=0.011). CONCLUSIONS: Our results suggest that the bone anabolic effect of GH replacement therapy could in part be mediated by a positive bone balance at each remodeling unit due to the inhibitory action of OPG on osteoclastogenesis.