Symmetric polymicrogyria and pachygyria associated with TUBB2B gene mutations

The purpose of the study is to explore the causative role of TUBB2B gene mutations in patients with different malformations of cortical development. We collected and evaluated clinical and MRI data of a cohort of 128 consecutive patients (61 females and 67 males) in whom brain MRI had detected a spectrum of malformations of cortical development including polymicrogyria or pachygyria, who were mutation-negative to other possible causative genes. Mutation analysis of the TUBB2B gene was performed. We identified three new TUBB2B mutations in three unrelated patients (3 out of 128; 2.3%) with a diffuse and rather symmetrical cortical abnormality, including diffuse polymicrogyria in two and bilateral regional pachygyria in one. One patient harbored a p.Asp417Asn amino-acid substitution in the C-terminal domain of the protein; one patient a p.Asn256Ser amino-acid substitution in the intermediate domain and one patient a p.Leu117Pro amino-acid substitution in the N-terminal domain. The localization of each mutation within the secondary structure of the β2-tubulin polypeptide suggests that these mutations might alter the proper functions of microtubules. The phenotypic spectrum associated with TUBB2B mutations is wider than previously reported and includes diffuse, symmetric malformations of cortical development.