IgA deficiency, epilepsy, and phenytoin treatment.

In a prospective study of thirty-two children with seizures treated with phenytoin (diphenylhydantoin), five had low levels of serum-IgA before treatment. All of these were among the fifteen who had had febrile convulsions in infancy. IgA levels fell significantly during 6 months treatment in the fourteen patients studied sequentially. Treated children with low serum-IgA had normal numbers of lymphocytes with surface IgA. This suggests that phenytoin causes failure of terminal differentiation of B lymphocytes, and is the first known cause of this, the commonest mechanism of immunoglobulin deficiency.