title: Risk factors for trisomy 21: maternal cigarette smoking and oral contraceptive use in a population-based case-control study.
abstract: OBJECTIVE
  We examined maternal smoking and oral contraceptive use as possible risk factors in the genesis of cases of trisomy 21 of maternal origin. This is the first epidemiological study to categorize cases of trisomy 21 by parent of origin and timing of the meiotic error before assessing possible risk factors.
  
  
  METHODS
  We used chromosome 21-specific DNA markers to assign origin to each case. Structured interviews were employed to determine maternal smoking and oral contraceptive use around conception.
  
  
  RESULTS
  The odds ratio (OR) for maternal smoking was significantly increased among younger mothers (OR = 2.98; 95% CI = 1.01-8.87), but only in a particular subset of meiotically-derived cases. The combined use of cigarettes and oral contraceptives increased the risk further (OR = 7.62; 95% CI = 1.63-35.6); however, oral contraceptive use alone was not a significant risk factor.
  
  
  CONCLUSIONS
  Our results indicate that categorizing cases of trisomy 21 by parent and timing of the meiotic error allows more precision in identifying risk factors and may shed light on mechanisms of meiotic nondisjunction.
authors.affiliation: Division of Birth Defects and Developmental Disabilities and the Office of Genetics and Disease Prevention, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Georgia 30341, USA. qay0@cdc.gov
authors.forename: Q
authors.initials: Q
authors.lastname: Yang
authors.forename: S L
authors.initials: SL
authors.lastname: Sherman
authors.forename: T J
authors.initials: TJ
authors.lastname: Hassold
authors.forename: K
authors.initials: K
authors.lastname: Allran
authors.forename: L
authors.initials: L
authors.lastname: Taft
authors.forename: D
authors.initials: D
authors.lastname: Pettay
authors.forename: M J
authors.initials: MJ
authors.lastname: Khoury
authors.forename: J D
authors.initials: JD
authors.lastname: Erickson
authors.forename: S B
authors.initials: SB
authors.lastname: Freeman
mesh_terms: D000328:Adult; D015139:Blotting, Southern; D016022:Case-Control Studies; D003276:Contraceptives, Oral / Q000009:adverse effects*; D004314:Down Syndrome / Q000453:epidemiology* / Q000209:etiology / Q000235:genetics; D004347:Drug Interactions; D015981:Epidemiologic Factors; D005260:Female; D005819:Genetic Markers; D006801:Humans; D007231:Infant, Newborn; D007407:Interviews as Topic; D016017:Odds Ratio; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D012307:Risk Factors; D012907:Smoking / Q000009:adverse effects*; D011795:Surveys and Questionnaires
chemical_list: D003276:Contraceptives, Oral; D005819:Genetic Markers