Investigators in Genetics, Pediatrics, Neurology, and Immunology, at Mansoura Un., Mansoura, Egypt found a gene frequency of 0.284 (c.f. 0.093 in controls) and a highly significant association between HLA-B5 antigen and febrile convulsions in 39 patients compared to 380 healthy controls. The high frequency of HLA-B5 antigen (48.7 in patients c.f., 17.6 in controls) reflected a significantly high relative risk and indicated that children having antigen B5 are 4.4 times more susceptible to febrile convulsions than those without that antigen. The means of IgA (89 mg%) and E-rosette (54%) were significantly low c.f. controls (151 and 64, respectively). The authors suggest that the genetic control of febrile convulsions is in linkage disequilibrium with HLA-B5, low IgA and low total T-cells and that this altered immune function may predispose to acute infections and high fever which precipitate the febrile convulsions. 
COMMENT: Ehrengut W and Ehrengut J  found a lack of immunoglobulins beta-2A and beta-2M and a reduction of gamma globulin in 4 of 6 patients and postulated a weakness of defense mechanisms against infection as a possible cause of febrile convulsions. This report was the first and only reference to hypoimmunoglobulinemia cited in the monograph Febrile Convulsions 1968 MacMillan, N.Y., which included a review of world literature published in English and foreign languages. Isaac et al  reported low serum IgA in children with febrile convulsions and Grob and Herold  and others have found IgA deficiency among epileptics receiving anticonvulsants, especially hydantoins (see Hafez et al).
The multifactorial inheritance of febrile seizures is alluded to in the 6th annual Merritt-Putnam Symposium . Siblings have approximately a 8-12% risk of alio having febrile seizures. If the index child and one parent are affected, the risks to siblings are 30-40% (50% if both parents are affected). A high proportion of probands and their siblings develop EEG abnormalities 3-5 years after the febrile seizure, including generalized spike-and-wave and a photoconvulsive response (Hauser et al 1985; Millichap, 1968).