Epilepsy, Anticonvulsants and Congenital Malformations

Summary

The dysmorphogenic potential of the anticonvulsant drug phenytoin in laboratory animals has been known for a number of years. In 1968 an association was noted between the occurrence of congenital abnormalities in man, particularly cleft lip with or without cleft palate, and the use of anticonvulsant drugs during pregnancy. Since then a number of surveys into the outcome of pregnancy in epileptic women have shown that there is an increased incidence of malformations in the children. This incidence has varied in the different reports from 15 % to 4 %, with an average incidence recorded in 9 major surveys of 7 %. The risk of an epileptic woman having a malformed baby has been estimated by most authors to be 2 to 3 times greater than in the general population. The most common malformations have been cleft lip with or without cleft palate and congenital heart disease, and it seems possible that these 2 types of malformations may occur together much more often than has previously been reported. A wide variety of other abnormalities involving most of the major organ systems of the body have also occurred.

The aetiology of these malformations is uncertain and a number of factors both genetic and environmental have to be considered. Whilst there appears to be a definite association between anticonvulsant therapy and the birth of a malformed infant, the incidence of malformations in the children of epileptic mothers not taking anticonvulsants is thought to be the same as in the general population. This suggests that the dysmorphogenic effect is not due to the epileptic disorder alone, although it may be argued that those women not taking anticonvulsants may have a milder form of epilepsy. Neither the duration of epilepsy nor the frequency of convulsions is related to the development of a malformed baby.

The majority of malformations have occurred in association with the use of phenytoin, primidone and phenobarbitone, either alone or in combination with one another, and to a lesser extent in combination with other anticonvulsants. However, the drug with the most likely dysmorphogenic potential is phenytoin. In mice, the dysmorphogenic effect of phenytoin is day and dose dependent and may be partially prevented by the administration of folic acid supplements. Folate deficiency is a potent dysmorphogen in rats, and there is some evidence that it may have the same effect, although to a lesser extent, in man. Phenytoin and primidone are known to cause folate deficiency in epileptic patients, and the view that the apparent dysmorphogenic effect is mediated by impaired folate metabolism is an attractive one that needs further study.

Phenytoin is also known to cause chromosome aberrations in vitro, and to alter nucleic acid metabolism, collagen metabolism and adrenocortical function. Any one of these actions is potentially dysmorphogenic. Although there may also be a genetic relationship between epilepsy and cleft lip and palate, and possibly other malformations as well, at present it is impossible to estimate the extent of this relationship.

The risk of an epileptic mother having a malformed child is in the region of 1 in 10, but at present there is no clear indication for altering her anticonvulsant therapy merely because of pregnancy. Anticonvulsants are valuable and essential drugs and their use must be continued. Phenytoin and folic acid levels in the plasma should be monitored in all epileptic women of child-bearing age, and folic acid supplements given if necessary. The epileptic woman should not be made aware of any potential risk of malformation and should be encouraged in her desire to have children.