MedGen

PAFAH1B1-related lissencephaly/subcortical band heterotopia (SBH) comprises a spectrum of severity. Affected newborns typically have mild-to-moderate hypotonia, feeding difficulties, and poor head control. During the first years, neurologic examination typically demonstrates poor visual tracking and response to sounds, axial hypotonia, and mild distal spasticity that can transition over time to more severe spasticity. Seizures occur in more than 90% of individuals with lissencephaly and often include infantile spasms. Seizures are often drug resistant, but even with good seizure control, the best developmental level achieved (excluding the few individuals with partial lissencephaly) is the equivalent of about age three to five months. In individuals with PAFAH1B1-related lissencephaly/SBH, developmental delay ranges from mild to severe. Other findings in PAFAH1B1-related lissencephaly/SBH include feeding issues and aspiration (which may result in need for gastrostomy tube placement), progressive microcephaly, and occasional developmental regression. [from GeneReviews]

Lissencephaly-5 (LIS5) is an autosomal recessive brain malformation characterized by cobblestone changes in the cortex, more severe in the posterior region, and subcortical band heterotopia. Affected individuals have hydrocephalus, seizures, and severely delayed psychomotor development (Radmanesh et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of lissencephaly, see LIS1 (607432). [from OMIM]

Van Maldergem syndrome is an autosomal recessive disorder characterized by intellectual disability, typical craniofacial features, auditory malformations resulting in hearing loss, and skeletal and limb malformations. Some patients have renal hypoplasia. Brain MRI typically shows periventricular nodular heterotopia (summary by Cappello et al., 2013). For a discussion of genetic heterogeneity of Van Maldergem syndrome, see 601390. [from OMIM]

Van Maldergem syndrome is an autosomal recessive disorder characterized by intellectual disability, typical craniofacial features, auditory malformations resulting in hearing loss, and skeletal and limb malformations. Some patients have renal hypoplasia. Brain MRI typically shows periventricular nodular heterotopia (summary by Cappello et al., 2013). Genetic Heterogeneity of Van Maldergem Syndrome See also VMLDS2 (615546), caused by mutation in the FAT4 gene (612411) on chromosome 4q28. [from OMIM]

Any complex cortical dysplasia with other brain malformations in which the cause of the disease is a mutation in the TUBB gene. [from MONDO]

Any complex cortical dysplasia with other brain malformations in which the cause of the disease is a mutation in the TUBG1 gene. [from MONDO]

Any complex cortical dysplasia with other brain malformations in which the cause of the disease is a mutation in the KIF2A gene. [from MONDO]

Band heterotopia (BH) is a neuronal migration disorder in which aberrantly located neurons, in the form of a band in the brain white matter, are present below a cortex that appears relatively normal by magnetic resonance imaging (MRI). Clinically, patients show severe developmental delay with intellectual disability, seizures, hypotonia, and hydrocephalus (Kielar et al., 2014, Shaheen et al., 2017). [from OMIM]

Complex cortical dysplasia with other brain malformations-15 (CDCBM15) is an autosomal recessive neurologic disorder characterized by progressive microcephaly associated with abnormal facial features, hypotonia, and variable global developmental delay with impaired intellectual development. Brain imaging shows variable malformation of cortical development on the lissencephaly spectrum, mainly pachygyria and thin corpus callosum (summary by Mitani et al., 2019). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039). [from OMIM]

Subcortical band heterotopia is a condition in which nerve cells (neurons) do not move (migrate) to their proper locations in the fetal brain during early development. (Heterotopia means "out of place.") Normally, the neurons that make up the outer surface of the brain (cerebral cortex) are distributed in a well-organized and multi-layered way. In people with subcortical band heterotopia, some neurons that should be part of the cerebral cortex do not reach it. These neurons stop their migration process in areas of the brain where they are not supposed to be and form band-like clusters of tissue. Since these bands are located beneath the cerebral cortex, they are said to be subcortical. In most cases, the bands are symmetric, which means they occur in the same places on the right and left sides of the brain.

The abnormal brain development causes neurological problems in people with subcortical band heterotopia. The signs and symptoms of the condition depend on the size of the bands and the lack of development of the cerebral cortex. The signs and symptoms can vary from severe intellectual disability and seizures that begin early in life and affect both sides of the brain (generalized seizures) to normal intelligence with seizures occurring later in life and affecting only one side of the brain (focal seizures). Some affected individuals also have weak muscle tone (hypotonia), loss of fine motor skills such as using utensils, or behavioral problems. Subcortical band heterotopia is typically found when brain imaging is done following the onset of seizures, usually in adolescence or early adulthood. [from MedlinePlus Genetics]