The hallmark feature seen in patients with TUBB2B mutations is asymmetric polymicrogyria (PMG). PMG is a brain malformation with numerous small gyri separated by shallow sulci, creating a cobblestone appearance. PMG in these patients is usually bilateral, asymmetric, and more striking in the frontal and temporal lobes. Other findings on MRI include absence of the corpus callosum, abnormal basal ganglia and cerebellum, and hypoplasia of the brainstem. Most patients also have microcephaly, severe mental retardation and seizures. Mutations of the TUBB2B gene have been identified in patients with asymmetrical PMG. Jaglin XH, et al  reported four unrelated individuals and one fetus with asymmetrical PMG and de novo mutations in TUBB2B. All mutations were missense mutations in highly conserved residues in exon 4. These mutations result in haploinsufficiency and aberrant heterodimer assembly. Mutations in TUBB2B are autosomal dominant and all mutations, to date, have been de novo. To date, no deletions/duplications in the TUBB2B gene have been reported as causative of polymicrogyria.
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