A TEST OF THE IMMUNOREACTIVE THEORY OF THE ORIGIN OF NEURODEVELOPMENTAL DISORDERS - IS THERE AN ANTECEDENT BROTHER EFFECT

Gualtieri and Hicks (1985) proposed that male vulnerability to neurode velopmental disorders (NDs) could be explained by maternal immune atta ck on the male fetus, especially among children whose mothers had prev iously conceived boys as opposed to girls. This antecedent brother eff ect was attributed to the build-up of maternal antibodies against prev ious male fetuses. Our sample consisted of 11,578 mother-child pairs w ho were followed up until 7 years old. For only one ND-mental retardat ion-was there a true antecedent brother effect: Mentally retarded boys were significantly more likely to have antecedent brothers than siste rs, whereas mentally retarded girls did not show this effect. Moreover , the incidence of mental retardation was elevated significantly among boys with at least two, as opposed to one, antecedent brothers. This did not occur among boys with antecedent sisters or in girls irrespect ive of antecedent sibling gender or number. This supports Gualtieri an d Hicks's immunoreactive theory for the origin of NDs for only one spe cific ND: mental retardation.