Role of polymorphisms in dopamine synthesis and metabolism genes and association of DBH haplotypes with Parkinson's disease among North Indians.

OBJECTIVES: Genetic and non-genetic components are believed to govern the etiology of common complex traits such as Parkinson's disease (PD). In view of the biochemical evidence of depleted dopamine levels in the affected brains and also the most common and effective therapeutic modality of administration of levodopa in PD, genes from the dopaminergic pathway emerge as major determinants. We have earlier shown the role of DRD4-120 bp duplication marker in PD susceptibility. In this study, contribution of six genes involved in dopamine synthesis and metabolism to PD susceptibility and disease severity was assessed in a North Indian PD cohort. METHODS: 339 patients diagnosed using UKPD brain bank criteria and 344 matched controls were recruited and disease severity was assessed using the Hoehn and Yahr scale and Unified Parkinson Disease Rating Scale III scores. Allelic, genotypic and haplotypic associations with PD were computed; severity was compared among the genotypic categories of markers; gene-gene interactions were assessed using multiple logistic regression. RESULTS: A highly significant association of dopamine beta-hydroxylase (DBH) haplotypes (rs1611115T>C - rs1108580A>G - rs5320A>G - rs129882C>T) with PD was observed; haplotypes C-A-G-C [P=0.000005, Odds ratio (95% confidence interval): OR (95% CI)=1.76 (1.38-2.25)] and C-A-G-T [P=0.000001, OR (95% CI)=0.49 (0.37-0.65)] retaining significance after Bonferroni correction. rs129882, a 3'UTR SNP in DBH showed significant association with disease severity [Hoehn and Yahr (P=0.005) and Unified Parkinson Disease Rating Scale (P=0.006)]. CONCLUSION: Observed association of DBH SNP/SNP haplotypes with PD susceptibility and its role in modulating disease severity reiterates the importance of dopamine pathway in sporadic PD etiology in general and potential therapeutic implications of DBH in particular.

Do motor control genes contribute to interindividual variability in decreased movement in patients with pain?

BACKGROUND: Because excessive reduction in activities after back injury may impair recovery, it is important to understand and address the factors contributing to the variability in motor responses to pain. The current dominant theory is the "fear-avoidance model", in which the some patients' heightened fears of further injury cause them to avoid movement. We propose that in addition to psychological factors, neurochemical variants in the circuits controlling movement and their modification by pain may contribute to this variability. A systematic search of the motor research literature and genetic databases yielded a prioritized list of polymorphic motor control candidate genes. We demonstrate an analytic method that we applied to 14 of these genes in 290 patients with acute sciatica, whose reduction in movement was estimated by items from the Roland-Morris Disability Questionnaire. RESULTS: We genotyped a total of 121 single nucleotide polymorphisms (SNPs) in 14 of these genes, which code for the dopamine D2 receptor, GTP cyclohydrolase I, glycine receptor alpha1 subunit, GABA-A receptor alpha2 subunit, GABA-A receptor beta1 subunit, alpha-adrenergic 1C, 2A, and 2C receptors, serotonin 1A and 2A receptors, cannabinoid CB-1 receptor, M1 muscarinic receptor, and the tyrosine hydroxylase, and tachykinin precursor-1 molecules. No SNP showed a significant association with the movement score after a Bonferroni correction for the 14 genes tested. Haplotype analysis of one of the blocks in the GABA-A receptor beta1 subunit showed that a haplotype of 11% frequency was associated with less limitation of movement at a nominal significance level value (p = 0.0025) almost strong enough to correct for testing 22 haplotype blocks. CONCLUSION: If confirmed, the current results may suggest that a common haplotype in the GABA-A beta1 subunit acts like an "endogenous muscle relaxant" in an individual with subacute sciatica. Similar methods might be applied a larger set of genes in animal models and human laboratory and clinical studies to understand the causes and prevention of pain-related reduction in movement.

Reliable screening for a pain-protective haplotype in the GTP cyclohydrolase 1 gene (GCH1) through the use of 3 or fewer single nucleotide polymorphisms.

BACKGROUND: A haplotype in the GTP cyclohydrolase 1 (dopa-responsive dystonia) gene (GCH1) is associated with decreased persistent pain. The aim of the present study was to develop a screening method for the pain-protective haplotype. METHODS: Complete genetic information for all 15 GCH1 DNA positions constituting the pain-protective GCH1 haplotype was available from 278 patients. In silico analyses, including discriminant analysis of the most frequent haplotypes, identified distinctive DNA positions that allow detection of the pain-protective haplotype at high sensitivity and specificity with the smallest possible number of DNA positions. Pyrosequencing(trade mark) assays were subsequently developed for these DNA positions, established with 662 DNA samples from healthy volunteers, and prospectively validated with a random selection of DNA samples genotyped for all 15 DNA positions. RESULTS: Diagnosis of the pain-protective GCH1 haplotype was possible with 100% sensitivity and specificity by screening for just 3 GCH1 genetic variants that span the entire DNA range of the haplotype: c.-9610G>A (dbSNP rs8007267G>A) in the 5' untranslated region, c.343 + 8900A>T (dbSNP rs3783641A>T) in intron 1, and c.*4279 (dbSNP rs10483639C>G) in the 3' untranslated region. Test sensitivity and specificity were still >95% with 2 or even just 1 of these GCH1 DNA positions. CONCLUSIONS: In silico analysis of complex GCH1 gene haplotypes reduced the requisite number of tested DNA positions from 15 to 3 while maintaining the reliability, specificity, and sensitivity of the genetic diagnosis. This screening method could reduce laboratory diagnostic efforts and facilitate investigations of the pain-protective GCH1 haplotype.