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Several single-nucleotide polymorphisms (SNPs) in the catechol-O-methyltransferase (COMT) gene have been associated with the risk of developing Parkinson’s disease (PD). We conducted a systematic review and a meta-analysis including all the studies published on PD risk related with COMT SNPs (mainly rs4680). We also reviewed the possible relationship of COMT SNPs with clinical, neuropharmacological, neurochemical, and neuroimaging features of PD.The systematic review was conducted using several databases. Meta-analysis of the eligible studies was carried out using the software Meta-Disc 1.1.1. Heterogeneity between studies was tested using the Q-statistic.The meta-analysis included 24 association studies for the COMT rs4680 SNP (9719 PD patients, 14 634 controls) and the risk for PD. The frequency of allele positivity showed a significant association between rs4680 and the risk for PD in the total series, as well as homozygosity for the low-activity allele in the Asiatic population (these associations were marginal or disappeared when studies on Hardy-Weinberg disequilibrium were not considered). Global diagnostic odds ratios (95% confidence intervals) for rs4680 were 0.99 (0.94-1.04) for the total group, 0.99 (0.93-1.05) for White, and 1.05 (0.90-1.22) for Asiatic individuals. COMT genotypes could be related with a modest modification in the age at onset of PD, but its possible genotypes in excessive daytime somnolence, impulse control disorders, cognitive impairment, and neuropharmacological or neurochemical variables are unclear.The results of the meta-analysis suggest that the COMT rs4680 polymorphism is not a major determinant of either the risk for PD or clinical, neuropharmacological and neurochemical features of PD. Data on other COMT polymorphisms are scarce but do not suggest association with PD. [ABSTRACT FROM AUTHOR]

A recent genome-wide association study and other replication studies have suggested that the rs3794087 single nucleotide polymorphism in the solute carrier family 1 - glial affinity glutamate transporter-member 2 (SLC1A2) gene is associated with an increased risk for essential tremor (ET), and a replication study in an Asian cohort has shown a decreased risk for ET associated with the rs3794087T allele. We tried to replicate this association in a White Spanish population.We analyzed the distribution of allelic and genotypic frequencies of rs3794087 in 202 patients with familial ET and 308 healthy controls using a TaqMan-based quantitative PCR assay.Genotypic and allelic frequencies of rs3794087 did not differ significantly between patients with ET and controls and were unrelated with the age at onset of tremor or sex.Our study suggests that SLC1A2 rs3794087 is not associated with the risk for developing familial ET in the Spanish population, thus subtracting relevance to SLC1A2 rs3794087 as a risk biomarker for ET. [ABSTRACT FROM AUTHOR]

Information on CYP2B6 allele frequencies and detrimental genotypes in mixed human populations is scarce. The aim of this study was to analyze the frequencies and haplotypes of nonsynonymous CYP2B6 single nucleotide polymorphisms (SNPs) in a Colombian population.One hundred and fifty-two healthy individuals were analyzed for five nonsynonymous CYP2B6 SNPs, namely rs8192709, rs3745274, rs2279343 rs28399499, and rs3211371.Besides eight known variant alleles, we identified two as yet unknown variant alleles combining, respectively, the SNPs rs3745274 and rs3211371 and rs8192709 and rs3745274. Comparison of Colombian mestizo individuals with other mestizo population indicates statistically significant differences (P<0.001) for the gain-of-function CYP2B6∗4 allele and for combined detrimental CYP2B6 alleles. In addition, we observed a low linkage between the SNPs rs3745274 and rs2279343, which are often assumed as linked.In conclusion, large interethnic and intraethnic variability exists for CYP2B6 polymorphisms, thus reinforcing the need for tailored genotyping protocols for CYP2B6 testing as a biomarker of drug response. [ABSTRACT FROM AUTHOR]

Oxidative stress and iron deposition is related to Parkinson's disease (PD). Heme oxygenase 2 (HMOX2) catalyzes the cleavage of the heme ring to form biliverdin with release of iron and carbon monoxide. This study aims to analyze variations in the HMOX2 gene in patients with PD.We mapped four single nucleotide polymorphisms (SNPs) and copy number variations of the HMOX2 gene in 691 patients with PD and 747 healthy individuals.We identified a highly homogeneous association of the HMOX2 SNP rs2270363 homozygous G/G genotype with patients with classical PD phenotype compared with healthy individuals. We identified three patients with PD and two control individuals with a single copy of the HMOX2 gene. No individuals with zero or more than two gene copies were identified.We describe for the first time, copy number variations in the HMOX2 gene and an association of the SNP rs2270363 with PD risk. [ABSTRACT FROM AUTHOR]

Some clinical and experimental data suggest a possible role of γ-aminobutyrate (GABA)-ergic mechanisms in the pathophysiology of essential tremor (ET). We studied the allelic and genotype frequencies of the single nucleotide polymorphisms, such as GABRA4-L26M (Leu26Met, rs2229940), GABRE-S102A (Ser26Ala, rs1139916), and GABRQ-I478F (Ile26Phe, rs3810651), in 200 patients with familial ET and 250 healthy controls using TaqMan genotyping. GABRA4-L26M, GABRE-S102A, and GABRQ-I478F genotype and allelic frequencies did not differ significantly between patients with ET and controls, and were unrelated to the age at onset of tremor or sex. The GABRQ-478F allele seemed to be related to improvement of tremor with ethanol use among men (odds ratio=2.32, 95% confidence interval=0.26-4.3, P=0.007, Pc=0.021). The results of this study suggest that the single nucleotide polymorphisms studied in the GABRA4, GABRE, and GABRQ genes are not related to the risk for familial ET. [ABSTRACT FROM AUTHOR]