Background: Neural tube defects (NTDs) and birth defects overall are more likely to occur among maternal compared to paternal relatives in two generations (uncles/aunts and first cousins) of Irish families where an individual has been born with an NTD.
Aims: The aim of this study was to determine if the matrilineal excess persisted into the third generation.
Methods: First cousins were interviewed about their pregnancy outcomes and their offsprings' health.
Results: Maternal first cousins once removed (FCOR) were more likely to have birth defects than paternal FCOR: 6.7 versus 3.5% (adjusted odds ratio 1.49, 95% CI 0.57, 3.89). No NTDs occurred. Folic acid supplementation significantly reduced the risk of birth defects (P = 0.04).
Conclusions: This study demonstrates an excess of birth defects among maternal relatives in three consecutive generations of NTD families, and supports the hypothesis that an underlying mechanism links distant maternal relatives in at least some NTD families.