title: Twin mothers, pregnancy hypertension and pre-eclampsia.
abstract: OBJECTIVE
  To estimate the maternal genetic contribution to the hypertensive diseases of pregnancy.
  
  
  METHODS
  A cohort study of female twins with information on hypertensive diseases of pregnancy obtained by questionnaire screening, and verification of diagnosis from hospital or general practitioner records.
  
  
  METHODS
  A volunteer twin registry in the UK with recruitment through the media without reference to pregnancies or disease status.
  
  
  METHODS
  Adult female, same-sex twin pairs who completed a pregnancy history questionnaire and consented to record inspection.
  
  
  METHODS
  Self-reported and hospital-validated diagnosis of non-proteinuric pregnancy hypertension and of pregnancy hypertension with proteinuria (pre-eclampsia).
  
  
  RESULTS
  Self-reported pre-eclampsia had a heritability of 0.221 and non-proteinuric hypertension of 0. 198. However, none of the pairs who were self-reported as concordant for pre-eclampsia were confirmed from hospital records. Using hospital records, the heritability of pre-eclampsia was 0 and 0.375 for non-proteinuric hypertension. Using a model treating pre-eclampsia as a separate disease from non-proteinuric hypertension, and assuming that the next pair identified was both monozygotic and concordant for pre-eclampsia, the estimated heritability of pre-eclampsia remained 0 (95% CI 0-0.49). Using a threshold model in which non-proteinuric hypertension is treated as a mild form of pre-eclampsia, heritability is estimated at 0.247 (95% CI 0.23-0.454).
  
  
  CONCLUSIONS
  Neither non-proteinuric hypertension nor pre-eclampsia are inherited in simple Mendelian fashion. The genetic contribution to multi-factorial inheritance is smaller than hitherto believed.
authors.affiliation: Centre for Reproduction, Growth and Development, Leeds University and Leeds General Infirmary, UK.
authors.forename: J G
authors.initials: JG
authors.lastname: Thornton
authors.forename: A M
authors.initials: AM
authors.lastname: Macdonald
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D006801:Humans; D006973:Hypertension / Q000235:genetics*; D011225:Pre-Eclampsia / Q000235:genetics*; D011247:Pregnancy; D011249:Pregnancy Complications, Cardiovascular; D011795:Surveys and Questionnaires