Variations in the alpha2A-adrenergic receptor gene and their functional effects.

BACKGROUND AND OBJECTIVES: The alpha2A-adrenergic receptor (ADRA2A) plays a central role in the regulation of systemic sympathetic activity and hence cardiovascular responses such as heart rate and blood pressure. The objectives of this study were to systematically search for variants in the ADRA2A gene, to define the gene's haplotype structure, and to examine potential functional effects of these variants. METHODS: We examined 5957 base pairs of contiguous sequence of ADRA2A (promoter, exonic, and 3'-flanking region) using polymerase chain reaction to amplify the genomic target, followed by bidirectional sequencing, in 135 healthy subjects (85 white and 50 black subjects). Haplotypes were inferred by use of an expectation-maximization algorithm. Primary (plasma norepinephrine concentration) and secondary (resting heart rate and blood pressure) phenotypes were compared among subjects grouped by individual polymorphisms and haplotypes. RESULTS: We identified 41 variants, including 24 novel variants. On the basis of 9 optimally selected markers, 11 haplotypes in 5 haplotype groups were inferred, representing approximately 99% of the cohort. Two uncommon variants in complete linkage disequilibrium (G>C at -1903 and C>G at -1607, identified in 3 black subjects) were associated with significantly increased plasma norepinephrine concentrations (376.7 +/- 6.1 pg/mL versus 218.4 +/- 95.0 pg/mL, P = .011). There was no other significant association between genetic variants or any of the haplotypes with phenotypes. CONCLUSION: We describe novel variants and the haplotype structure of the ADRA2A gene. Common genetic ADRA2A variants are not important determinants of baseline cardiovascular measures (plasma norepinephrine, heart rate, and blood pressure) in healthy volunteers.

Genetic variation in eleven phase I drug metabolism genes in an ethnically diverse population.

The extent of genetic variation found in drug metabolism genes and its contribution to interindividual variation in response to medication remains incompletely understood. To better determine the identity and frequency of variation in 11 phase I drug metabolism genes, the exons and flanking intronic regions of the cytochrome P450 (CYP) isoenzyme genes CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 and CYP3A5 were amplified from genomic DNA and sequenced. A total of 60 kb of bi-directional sequence was generated from each of 93 human DNAs, which included Caucasian, African-American and Asian samples. There were 388 different polymorphisms identified. These included 269 non-coding, 45 synonymous and 74 non-synonymous polymorphisms. Of these, 54% were novel and included 176 non-coding, 14 synonymous and 21 non-synonymous polymorphisms. Of the novel variants observed, 85 were represented by single occurrences of the minor allele in the sample set. Much of the variation observed was from low-frequency alleles. Comparatively, these genes are variation-rich. Calculations measuring genetic diversity revealed that while the values for the individual genes are widely variable, the overall nucleotide diversity of 7.7 x 10(-4) and polymorphism parameter of 11.5 x 10(-4) are higher than those previously reported for other gene sets. Several independent measurements indicate that these genes are under selective pressure, particularly for polymorphisms corresponding to non-synonymous amino acid changes. There is relatively little difference in measurements of diversity among the ethnic groups, but there are large differences among the genes and gene subfamilies themselves. Of the three CYP subfamilies involved in phase I drug metabolism (1, 2, and 3), subfamily 2 displays the highest levels of genetic diversity.

APOBEC3G expression and hypermutation are inversely associated with human immunodeficiency virus type 1 (HIV-1) burden in vivo.

APOBEC3G (A3G) and APOBEC3F (A3F) reduce Vif-negative HIV-1 provirus formation and cause disabling provirus G-to-A hypermutation in vitro. However, evidence conflicts about whether they negatively impact Vif-positive HIV-1, or only enhance virus genetic diversity, in vivo. We studied peripheral blood mononuclear cells (PBMC) from 19 antiretroviral-naïve, HIV-infected adults: 12 long-term non-progressors (LTNP) and 7 non-controllers (NC). Cells from LTNP had higher A3G and A3F mRNA levels, lower provirus burden, and more A3G-hypermutated positions in provirus sequence than cells from NC. A3G mRNA level was directly associated with its Hypermutation Index (HI) and inversely associated with provirus burden. Plasma HIV-1 RNA levels were inversely associated with A3G expression levels and with HI only among subjects who had HI>1. A3G HI was not associated with provirus burden. These results indicate that A3G deaminase-dependent activity above a threshold level, and its deaminase-independent functions, contribute to decreasing Vif-positive virus replication in vivo.

Variation in the alpha2B-adrenergic receptor gene (ADRA2B) and its relationship to vascular response in vivo.

The alpha2B-adrenergic receptor (ADRA2B) plays an important role in vasoconstriction and blood pressure regulation. One common variant in the ADRA2B gene (del 301--303) has been identified, and results in markedly decreased receptor desensitization in vitro but does not alter vascular sensitivity in vivo. Therefore, we fully characterized genetic variations in ADRA2B and related them to phenotype in vivo. We examined 5812 bp of contiguous sequence of ADRA2B (promoter, exonic, and 3'-untranslated region; 3'-UTR) using the polymerase chain reaction to amplify the genomic target followed by bidirectional sequencing (n=68). Haplotypes were inferred using an expectation maximization algorithm. Vasoconstriction in response to increasing doses of the highly selective alpha2-adrenergic receptor agonist, dexmedetomidine (0.01--1000 ng/min) was measured in the dorsal hand vein using a linear variable differential transformer. The dose that produced 50% (ED50) of maximum venoconstriction (Emax) was determined for each subject from the individual dose--response curves. ED50 and Emax were compared in subjects with and without variant alleles and haplotypes of interest. We identified 24 variable sites, 12 in the promoter region, five in the coding region (including two previously described as non-synonymous variants) and seven in the 3'-UTR region. Four haplotypes were inferred, representing approximately 95% of the cohort. One haplotype, characterized by two single nucleotide polymorphisms in the promoter region, and one in the 3'-UTR, occurred in seven of 38 African-Americans, and was associated with a lower Emax, 61.3% [95% confidence interval (CI) 39.5--83.0, n=7] compared to 78.1% (CI 73.8--82.5) in wild-types (n=61) (P=0.02). There was no association between the nine common variants and dexmedetomidine ED50. We have described novel variants and haplotypes of the ADRA2B gene. These do not alter sensitivity to a selective alpha2-adrenergic receptor agonist but some may decrease maximal venoconstriction in vivo.