Clinical and genetic characteristics of type 3 lissencephaly caused by a mutation in the TUBA1A gene (OMIM: 611603)

Abstract

Background. Lissencephaly (LIS) is a spectrum of malformations of the cerebral cortex that occur as a result of impaired migration of neuronal precursors to the cortical plate and the formation of furrows and convolutions in the post‑migration period of embryonic development. In recent years, a significant role of hereditary factors in the occurrence of LIS has been shown due to the improvement of methods of molecular genetic diagnostics. Today, 13 genetic variants have been identified in the LIS group, six of which are inherited autosomal recessively, five are autosomal dominant, and two are linked to the X chromosome. It is shown that 80 % of cases of hereditary LIS is caused by mutations in two genes: PAFAH1B1, which is responsible for the occurrence of the LIS 1 type with an au‑ tosomal dominant type of inheritance, and in the DCX gene, localized on the X chromosome. The rest of the genetic variants account for from 1 % to 5 % of cases of defects accompanied by dysgenesis of the cerebral cortex. In recent years, the number of works devoted to the analysis of clinical and genetic characteristics of monogenic variants of LIS has increased. The results of such studies will allow us to improve our understanding not only of the pathogenetic mechanisms of this group of diseases, but also of the molecular basis for the formation of brain structures in the normal embryonic period.Objective: to describe the clinical and genetic characteristics of three Russian patients with autosomal dominant LIS type 3 (OMIM: 611603) caused by mutations in the TUBA1A gene.Materials and methods. All patients were under observation in the consultative and diagnostic department of Research Centre for Medical Genetics. The diagnosis was established on the basis of clinical data, genealogical anamnesis, results of brain MRI, EEG night video monitoring and exome sequencing by NGS. The validation of the identified nucleotide substitutions and analysis of the disease segregation were performed using the Sanger direct automatic sequencing method.Results. The clinical and genetic characteristics of three patients with newly identified and previously described mutation in the TUBA1A gene were analyzed. Possible effects of new missense mutations in the gene on the function of the protein product of the gene are discussed.Conclusions. The results of the analysis of the clinical and genetic characteristics of the patients we observed contribute to the study of the polymorphism of clinical manifestations resulting from mutations in the TUBA1A gene. The previously stated assumption about a wide range of malformations of the brain in patients with mutations in this gene was confirmed, which should be taken into account when making a diagnosis.

Keywords

• brain malformation
• lissencephaly
• microcephaly
• tubulin
• tuba1a