SEASONAL-VARIATION IN BIRTH DATE OF CHILDREN WITH CLEFT-LIP

Liability to neural tube defects is increased by maternal dietary defi ciency, and children with neural tube defects show a possibly related seasonal variation in date of birth. Since maternal dietary insufficie ncy may also increase liability to cleft lip, with or without cleft pa late (CLP), we wondered if children with CLP would also show a seasona l variation in birth date. The multifactorial threshold model predicts that any such effect would be more apparent in males than females, si nce CLP is more frequent in males. Month of birth was obtained from re cords of 598 children with CLP seen at The Montreal Children's Hospita l between 1950 and 1996. Children with syndromes or associated malform ations were excluded. There was a significant tendency for children wi th CLP to be born more often in the summer than in winter. The differe nce was greater in males than in females. The seasonal fluctuation in month of birth of children with CLP is consistent with the presence of an environmental factor increasing liability, with a maximal effect i n November-December. This might be related, at least in part, to a sea sonal fluctuation in maternal nutrition. The data support the predicti on that analyzing the data for the sexes separately would amplify the effects of variation in liability for a multifactorial threshold trait that has a different frequency in males and females. This approach co uld be useful in the study of other gene-environment interactions. (C) 1998 Wiley-Liss, Inc.