Maternal factors in cleft lip with or without palate: evidence from interracial crosses in the United States.
Maternal determinants of oral clefts have been documented in studies of experimental animals but not of humans. We studied maternal and paternal influences on the well-known differences in the incidence of oral clefts between Whites and Blacks in the United States. Using United States birth certificate data for 1973-1978, we compared the incidence of oral clefts in offspring of White-White, Black-Black, and White-Black couples. Because oral clefts are underreported on birth certificates, we also compared oral clefts as a proportion of all defects reported for offspring of various combinations of parental races. After adjusting for fathers race, offspring of White mothers had a higher rate of cleft lip with or without palate (CLP) than those of Black mothers (odds ratio [OR] = 2.33, P less than 10(-4] and a higher proportion of CLP in their reported defects (OR = 2.41, P less than 10(-4]. This maternal race effect did not apply to cleft palate (CP), and it persisted after adjusting for mother's age, parity, and education. However, after adjusting for mother's race, offspring of White fathers did not have a higher rate or proportion of CLP or CP than those of Black fathers. The study shows that the difference in the reported rates of CLP between Whites and Blacks is due to the effect of mother's race, whereas the difference in the reported rates of CP cannot be attributed to the independent effect of mother's or father's race. The study documents the existence of maternal determinants of CLP in humans.