title: DRD2 and PPP1R1B (DARPP-32) polymorphisms independently confer increased risk for autism spectrum disorders and additively predict affected status in male-only affected sib-pair families.
abstract: BACKGROUND
  The neurotransmitter dopamine (DA) modulates executive functions, learning, and emotional processing, all of which are impaired in individuals with autism spectrum disorders (ASDs). Our previous findings suggest a role for dopamine-related genes in families with only affected males.
  
  
  METHODS
  We examined two additional genes which affect DA function, the DRD2 and PPP1R1B (DARPP-32) genes, in a cohort of 112 male-only affected sib-pair families. Selected polymorphisms spanning these genes were genotyped and both family-based and population-based tests were carried out for association analysis. General discriminant analysis was used to examine the gene-gene interactions in predicting autism susceptibility.
  
  
  RESULTS
  There was a significantly increased frequency of the DRD2 rs1800498TT genotype (P = 0.007) in affected males compared to the comparison group, apparently due to over-transmission of the T allele (P = 0.0003). The frequency of the PPP1R1B rs1495099CC genotype in affected males was also higher than that in the comparison group (P = 0.002) due to preferential transmission of the C allele from parents to affected children (P = 0.0009). Alleles rs1800498T and rs1495099C were associated with more severe problems in social interaction (P = 0.0002 and P = 0.0016, respectively) and communication (P = 0.0004 and P = 0.0046), and increased stereotypic behaviours (P = 0.0021 and P = 0.00072). General discriminant analysis found that the DRD2 and PPP1R1B genes additively predicted ASDs (P = 0.00011; Canonical R = 0.26) and explain ~7% of the variance in our families. All findings remained significant following corrections for multiple testing.
  
  
  CONCLUSIONS
  Our findings support a role for the DRD2 and PPP1R1B genes in conferring risk for autism in families with only affected males and show an additive effect of these genes towards prediction of affected status in our families.
authors.affiliation: Department of Physiology, Queen's University, Kingston, ON, Canada.
authors.forename: Joe A
authors.initials: JA
authors.lastname: Hettinger
authors.forename: Xudong
authors.initials: X
authors.lastname: Liu
authors.forename: Melissa L
authors.initials: ML
authors.lastname: Hudson
authors.forename: Alana
authors.initials: A
authors.lastname: Lee
authors.forename: Ira L
authors.initials: IL
authors.lastname: Cohen
authors.forename: Ron C
authors.initials: RC
authors.lastname: Michaelis
authors.forename: Charles E
authors.initials: CE
authors.lastname: Schwartz
authors.forename: Suzanne M E
authors.initials: SM
authors.lastname: Lewis
authors.forename: Jeanette J A
authors.initials: JJ
authors.lastname: Holden
mesh_terms: D000483:Alleles; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000235:genetics*; D051937:Dopamine and cAMP-Regulated Phosphoprotein 32 / Q000235:genetics*; D056726:Genetic Association Studies; D056426:Genetic Loci; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006801:Humans; D015810:Linkage Disequilibrium; D008297:Male; D020641:Polymorphism, Single Nucleotide; D017448:Receptors, Dopamine D2 / Q000235:genetics*; D035781:Siblings
chemical_list: D051937:Dopamine and cAMP-Regulated Phosphoprotein 32; D017448:Receptors, Dopamine D2