Spina bifida cystica. Incidence of spina bifida occulta in parents and in controls.

It has been shown in an earlier paper (Lorber, 1965) dealing with the family history of 722 infants born with spina bifida cystica or encephalocele, that 6 8% of 1256 sibs were also affected, either by the same condition or by the closely allied lesions of anencephaly or congenital hydrocephalus. This high incidence in sibs is suggestive of hereditary factors playing a part in the causation of these disorders. Several earlier workers have also come to similar conclusions, and details of their contribution have been given in the quoted paper. In no series, however, is the incidence in sibs 1: 4, as one would expect in simple recessive transmission. Thus it appears possible either that there is multifactorial inheritance, or that extraneous factors need to be present for spina bifida to become manifest. It is suggested, however, that simple recessive inheritance is not altogether excluded for two reasons (Lorber, 1965). The first is that spina bifida is a potentially lethal condition even before birth, and the gene responsible for it may lead to very early foetal death with non-recognition of the defect, or even ofthe pregnancy. The second reason is that, as far as we are aware, there is no knowledge about the connexion between spina bifida cystica and spina bifida occulta. Spina bifida occulta is very common in the general population and may conceivably represent the mildest form of this disorder. If this reasoning were correct then the true incidence of these malformations in sibs could reach the proportion of 1: 4, as demanded by the laws of recessive inheritance. In order to get nearer to determining the influence of heredity in spina bifida cystica, we decided to investigate the relation between this condition and spina bifida occulta by determining the incidence of the latter among the parents of patients with spina bifida cystica. The incidence of spina bifida occulta in a control series of adults, drawn from the same population, was also determined.