title: Case-control and family-based association studies of candidate genes in autistic disorder and its endophenotypes: TPH2 and GLO1.
abstract: BACKGROUND
  The TPH2 gene encodes the enzyme responsible for serotonin (5-HT) synthesis in the Central Nervous System (CNS). Stereotypic and repetitive behaviors are influenced by 5-HT, and initial studies report an association of TPH2 alleles with childhood-onset obsessive-compulsive disorder (OCD) and with autism. GLO1 encodes glyoxalase I, the enzyme which detoxifies alpha-oxoaldehydes such as methylglyoxal in all living cells. The A111E GLO1 protein variant, encoded by SNP C419A, was identified in autopsied autistic brains and proposed to act as an autism susceptibility factor. Hyperserotoninemia, macrocephaly, and peptiduria represent some of the best-characterized endophenotypes in autism research.
  
  
  METHODS
  Family-based and case-control association studies were performed on clinical samples drawn from 312 simplex and 29 multiplex families including 371 non-syndromic autistic patients and 156 unaffected siblings, as well as on 171 controls. TPH2 SNPs rs4570625 and rs4565946 were genotyped using the TaqMan assay; GLO1 SNP C419A was genotyped by PCR and allele-specific restriction digest. Family-based association analyses were performed by TDT and FBAT, case-control by chi2, endophenotypic analyses for 5-HT blood levels, cranial circumference and urinary peptide excretion rates by ANOVA and FBAT.
  
  
  RESULTS
  TPH2 alleles and haplotypes are not significantly associated in our sample with autism (rs4570625: TDT P = 0.27, and FBAT P = 0.35; rs4565946: TDT P = 0.45, and FBAT P = 0.55; haplotype P = 0.84), with any endophenotype, or with the presence/absence of prominent repetitive and stereotyped behaviors (motor stereotypies: P = 0.81 and 0.84, verbal stereotypies: P = 0.38 and 0.73 for rs4570625 and rs4565946, respectively). Also GLO1 alleles display no association with autism (191 patients vs 171 controls, P = 0.36; TDT P = 0.79, and FBAT P = 0.37), but unaffected siblings seemingly carry a protective gene variant marked by the A419 allele (TDT P < 0.05; patients vs unaffected siblings TDT and FBAT P < 0.00001).
  
  
  CONCLUSIONS
  TPH2 gene variants are unlikely to contribute to autism or to the presence/absence of prominent repetitive behaviors in our sample, although an influence on the intensity of these behaviors in autism cannot be excluded. GLO1 gene variants do not confer autism vulnerability in this sample, but allele A419 apparently carries a protective effect, spurring interest into functional correlates of the C419A SNP.
authors.affiliation: Laboratory of Molecular Psychiatry and Neurogenetics, University Campus Bio-Medico, Via Longoni 83, I-00155 Rome, Italy. r.sacco@unicampus.it
authors.forename: Roberto
authors.initials: R
authors.lastname: Sacco
authors.forename: Veruska
authors.initials: V
authors.lastname: Papaleo
authors.forename: Jorg
authors.initials: J
authors.lastname: Hager
authors.forename: Francis
authors.initials: F
authors.lastname: Rousseau
authors.forename: Rainald
authors.initials: R
authors.lastname: Moessner
authors.forename: Roberto
authors.initials: R
authors.lastname: Militerni
authors.forename: Carmela
authors.initials: C
authors.lastname: Bravaccio
authors.forename: Simona
authors.initials: S
authors.lastname: Trillo
authors.forename: Cindy
authors.initials: C
authors.lastname: Schneider
authors.forename: Raun
authors.initials: R
authors.lastname: Melmed
authors.forename: Maurizio
authors.initials: M
authors.lastname: Elia
authors.forename: Paolo
authors.initials: P
authors.lastname: Curatolo
authors.forename: Barbara
authors.initials: B
authors.lastname: Manzi
authors.forename: Tiziana
authors.initials: T
authors.lastname: Pascucci
authors.forename: Stefano
authors.initials: S
authors.lastname: Puglisi-Allegra
authors.forename: Karl-Ludvig
authors.initials: KL
authors.lastname: Reichelt
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Persico
mesh_terms: D001321:Autistic Disorder / Q000235:genetics*; D016022:Case-Control Studies; D005819:Genetic Markers; D005838:Genotype; D006801:Humans; D007791:Lactoylglutathione Lyase / Q000235:genetics*; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D019655:Quantitative Trait, Heritable; D014365:Tryptophan Hydroxylase / Q000235:genetics*
chemical_list: D005819:Genetic Markers; C494784:TPH2 protein, human; D014365:Tryptophan Hydroxylase; D007791:Lactoylglutathione Lyase