Affected patients are generally divided into three groups, depending on the location of the formation: subependymal, subcortical, and band heterotopia. In addition, especially with heterotopia that are genetically linked, there are gender differences. Men seem to develop more severe symptoms than women with similar formations. In general, band heterotopia, also known as double cortex syndrome, are seen exclusively in women; men with a mutation of the related gene (called XLIS or DCX) usually die in utero or have a much more severe brain anomaly. Symptoms in affected women vary from normal to severe developmental delay or intellectual disability; the severity of the syndrome is related to the thickness of the band of arrested neurons. Nearly all affected patients that come to medical attention have epilepsy, with partial complex and atypical absence epilepsy being the most common syndromes. Some of the more severely affected patients develop drop attacks. Periventricular or subependymal
Periventricular means beside the ventricle, while subependymal (also spelled subepydymal) means beneath the ependyma; because the ependyma is the thin epithelial sheet lining the ventricles of the brain, these two terms are used to define heterotopia occurring directly next to a ventricle. This is by far the most common location for heterotopia. Patients with isolated subependymal heterotopia usually present with a seizure disorder in the second decade of life. Subependymal heterotopia present in a wide array of variations.
The DCX protein is thought to direct neuronal migration by regulating the organization and stability of microtubules, necessary for neuronal motility. The malformation is seen only in females, as the gene is found on the X-chromosome. Since there are two X chromosomes in females, after X-inactivation, only some neurons lose doublecortin function. These neurons with the mutant DCX gene fail to migrate into the cortex and thus form the underlying heterotopic band, while neurons which express the normal gene successfully migrate out to the cortical plate. Males with DCX mutations develop classical lissencephaly. Diagnosis
Detection of heterotopia generally occurs when a patient receives brain imaging—usually an MRI or CT scan—to diagnose seizures that are resistant to medication. Correct diagnosis requires a high degree of radiological skill, due to the heterotopias resemblance to other masses in the brain. Treatment
When seizures are present in any forms of cortical dysplasia, they are resistant to medication. Frontal lobe resection provides significant relief from seizures to a minority of patients with periventricular lesions. Prognosis
In general, gray matter heterotopia is fixed in both its occurrence and symptoms;  that is, once symptoms occur, it does not tend to progress. Varying results from surgical resection of the affected area have been reported. Although such surgery cannot reverse developmental disabilities, it may provide full or partial relief from seizures. Heterotopia are most commonly isolated anomalies, but may be part of a number of syndromes, including chromosomal abnormalities and fetal exposure to toxins (including alcohol).