MULTIFACTORIAL DISORDERS
A 32-year-old woman with corrected tetralogy of Fallot is pregnant at 18
weeks’ gestation with a male fetus. She inquires as to the chance that her
son has congenital heart disease.The majority of birth defects (70%) are multifactorial or polygenic in origin,
which means there is an interaction of multiple genes with environmental
factors. Characteristic Mendelian patterns are not found, but there is an
increased frequency of the disorder or phenotype in families. Overall
recurrence rate is 2–3%.
Examples of multifactorial inheritance include the following:
Neural tube defects Cleft lip and palate
Congenital heart disease Pyloric stenosisAs the number of genes for a multifactorial trait increases, the liability for the
disease increases.
The more severe the malformation, the higher the risk for recurrence.Neural tube defects (NTD) (1–2 per 1,000 births): The spectrum ranges from
anencephaly to very slight vertebral defects. Result from failure of neural tube
closure by day 22–28 postconception. Anencephaly and spina bifida occur
with equal frequency. Polyhydramnios is frequently seen.
Women at high risk for NTD should take 4 mg of folic
acid. Preconception folic acid supplementation may decrease incidence