Interrelationship of genetics and prenatal injury in the genesis of malformations of cortical development.

CONTEXT Although the causes of some malformations of cortical development (MCD) have been established, others remain unclear. There are several lines of evidence supporting the theory of a complex mechanism that involves genetic and environmental factors. OBJECTIVE To investigate the interrelationship of genetics and prenatal injury in the genesis of MCD. PATIENTS AND DESIGN A series of 76 consecutive patients with MCD and their families were systematically questioned about their family histories of epilepsy or other neurological impairment and the occurrence of prenatal events. Whenever possible, magnetic resonance imaging was performed in other family members if MCD was suspected or in the presence of any neurological impairment. Patients were divided into 3 groups according to the type of MCD. Patients in group 1 had focal cortical dysplasia, group 2 had heterotopias (periventricular or subcortical) or agyria-pachygyria, and group 3 had polymicrogyria or schizencephaly. These findings were also compared with a disease-control group of 40 consecutive patients with epilepsy but without MCD. SETTING Neurology clinic of a university hospital. RESULTS Of the 76 patients with MCD, 21 (28%) had focal cortical dysplasia, 19 (25%) had heterotopias or agyria-pachygyria, and 36 (47%) had polymicrogyria or schizencephaly. There were 39 men and 37 women, aged 2 to 52 years (mean age, 13 years). In group 2, 6 patients (32%) had a family history of MCD, mental retardation, or miscarriages, suggesting a genetic predisposition. In group 3, family history of MCD was present in 5 patients (14%). Prenatal events occurred in 28 patients with MCD (37%) and 2 controls (5%) and were more frequent in patients with heterotopia or agyria-pachygyria and polymicrogyria (P<.001). Conversely, epilepsy occurred in all patients in group 1, in 17 patients (89%) in group 2, and in 17 patients (47%) in group 3. In group 3, epilepsy was less frequent (P<.001) and also more easily controlled (P =.005) than in other forms of MCD. CONCLUSIONS Our findings support the idea of a spectrum among the different types of MCD. Focal cortical dysplasia (group 1) is associated with more frequent and severe epilepsy and less important genetic and prenatal events, heterotopias and agyria-pachygyria (group 2) are frequently associated with genetic predisposition, and polymicrogyria and schizencephaly (group 3) are less frequently associated with epilepsy but have a stronger association with genetic and detectable prenatal events.