A test of the immunoreactive theory of the origin of neurodevelopmental disorders: Is there an antecedent brother effect?

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Abstract
Gualtieri and Hicks (1985) proposed that male vulnerability to neurodevelopmental disorders (NDs) could be explained by maternal immune attack on the male fetus, especially among children whose mothers had previously conceived boys as opposed to girls. This antecedent brother effect was attributed to the build‐up of maternal antibodies against previous male fetuses. Our sample consisted of 11,578 mother‐child pairs who were followed up until 7 years old. For only one ND—mental retardation—was there a true antecedent brother effect: Mentally retarded boys were significantly more likely to have antecedent brothers than sisters, 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 irrespective of antecedent sibling gender or number. This supports Gualtieri and Hicks's immunoreactive theory for the origin of NDs for only one specific ND: mental retardation.