Schisis-association.

The neural tube defects (anencephaly, encephalocele, spina bifida cystica), oral clefts (cleft lip +/- palate, posterior cleft palate), omphalocele, and diaphragmatic hernia associate with one another far more frequently than at the expected random combination rates. The combination of other abnormalities does not exceed the expected rate. Thus, two or more combinations of schisis-type abnormalities without other defects were treated as a provisional entity. The schisis-association is practically a lethal abnormality. It occurs more often in girls (sex ratio: 0.33), in twins (4.6%), in breech presentations (13.7%), in association with lower mean birth weight (1,931 gm), and in association with a shorter gestation period (36.4 weeks). Mothers of affected children have a significantly higher miscarriage rate; occurrence of schisis-type abnormalities was found in 3.7% of the sibs of index patients. However, except for one, the sib-occurrences of schisis abnormalities were isolated neural tube defects or oral clefts.