title: The familial aggregation of the lesser variant in biological and nonbiological relatives of PDD probands: a family history study.
abstract: OBJECTIVE
  To determine the risk of the lesser variant (or PDD-like traits) in the biological and nonbiological second- and third-degree relatives of PDD probands using a screening questionnaire and to investigate the extent to which the risk of the lesser variant differs according to various characteristics of the proband.
  
  
  METHODS
  The sample consists of a series of 34 nuclear families with 2 affected PDD children (multiplex, MPX), 44 families with a single PDD child (simplex, SPX), and 14 families who adopted a PDD child. Data on characteristics of the lesser variant in 1362 biological and 337 nonbiological second- and third-degree relatives were collected from parents by telephone interview and from several maternal and paternal relatives by questionnaire.
  
  
  RESULTS
  All components of the lesser variant were more common in biological relatives (BR) than nonbiological relatives (NBR), confirming the familial aggregation of the traits. Proband characteristics associated with an increased risk of the lesser variant in relatives were a higher level of functioning and coming from a MPX family.
  
  
  CONCLUSIONS
  These findings on the familial aggregation of the lesser variant suggest that the genes for PDD also confer susceptibility to the lesser variant and that PDD may be a genetically heterogeneous disorder.
authors.affiliation: McMaster University, Hamilton, Canada. Szatmar@fhs.csu.mcmaster.ca
authors.forename: P
authors.initials: P
authors.lastname: Szatmari
authors.forename: J E
authors.initials: JE
authors.lastname: MacLean
authors.forename: M B
authors.initials: MB
authors.lastname: Jones
authors.forename: S E
authors.initials: SE
authors.lastname: Bryson
authors.forename: L
authors.initials: L
authors.lastname: Zwaigenbaum
authors.forename: G
authors.initials: G
authors.lastname: Bartolucci
authors.forename: W J
authors.initials: WJ
authors.lastname: Mahoney
authors.forename: L
authors.initials: L
authors.lastname: Tuff
mesh_terms: D000293:Adolescent; D000300:Adoption; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001321:Autistic Disorder / Q000235:genetics / Q000523:psychology; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000235:genetics* / Q000523:psychology*; D005190:Family / Q000523:psychology*; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D007223:Infant; D007360:Intelligence; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D012494:Sampling Studies; D017678:Sex Distribution; D011795:Surveys and Questionnaires