Authors :
Presenting Author: Wenwei Liu, MD – Peking University First Hospital
Miaomiao Chen, PhD – Peking University First Hospital; Yangyang Gan, PhD – Peking University Health Science Center; Ying Zhu, professer – Peking University First Hospital; Yufen Li, Doctor – Linyi People’s Hospital; Zhongyan Wu, PhD – eking University Health Science Center; Zhixian Yang, Professor – Peking University People’s Hospital; Fan Mei, PhD – Peking University Health Science Center; Yuxin Yin, Professor – Peking University Health Science Center; Yuehua Zhang, Professor – Peking University First Hospital
Rationale:
Tubulinopathies are a group of recently described entities, that lead to epilepsy, complex malformation of cortical development and developmental delay. Tubulin beta-2A chain (TUBB2A), a member of β-tubulin subunits, is the highest expression of β-tubulin in neurons. However, there are still few cases reported worldwide. This study will explore the clinical phenotypes and pathogenesis of
TUBB2A variant-related epilepsy.
Methods:
The clinical data of five patients with epilepsy in our cohort and 23 patients with epilepsy from nine published studies with the
TUBB2A variants were evaluated. Using
TUBB2A-FLAG and
TUBB2A-EGFP plasmids transfected HEK293T cells to overexpress
TUBB2A exogenously. Western Blot and immunofluorescence assays were used to examine the influence of
β-tubulins function by TUBB2A variants.
Results:
Four different TUBB2A variants were identified in five patients, and all of them carried heterozygous TUBB2A missense variants. One variant was identified in siblings. Three variants were de novo variants (p.Asp203Glu, p.Val229Ala, p.Arg391His), one was inherited variant, from their mosaic mother (p.Arg2Leu). All those four variants were novel variants. In all 28 cases, the seizure onset age ranged from neonate to eight years old, and 61% (17/28) of their seizures started before one year old. The common seizure types are epileptic spasms (32%), focal seizures (32%), myoclonic seizures (14%), and generalized tonic-clonic seizures (GTCS) (11%). All 28 patients showed varying degrees of developmental delay. In total 28 patients, 93% (26/28) of patients had malformation of cortical development (MCD). Their brain MRI showed microcephalus in 11 patients, dysgyria in 10 patients, pachygyria in six patients, polymicrogyria and cortical heterotopia are rare MCDs. Seventeen patients had agenesis of corpus callosum (ACC). Forty three percent (12/28) of the patients had enlarged ventricular. By predicting in three-dimensional (3D) structure, 64% (18/28) of the TUBB2A related epileptic variants located near or in linkage of tubulin dimers. Thirty three percent (6/18) of these patients might had severe clinical phenotypes, such as pachygyria. Our study examined the function of four novel TUBB2A variants in our five patients, and found the variants of TUBB2A could impact on microtubule stability, mitosis and spindle bipolarity, and affect tubulin TUBB2A incorporation into microtubules.
Conclusions:
All the variants of
TUBB2A were missense variants. Most of
TUBB2A related epileptic patients had seizures onset age before one year old. Focal seizures, epileptic spasms, myoclonic seizures and GTCS were the common seizure types. Dysgyria and ACC were the common phenotypes of MCD. All patients showed varying degrees of developmental delay. This study expended the variants spectrum of
TUBB2A, and confirmed that variants of
TUBB2A could impact on microtubule stability, mitosis and spindle bipolarity, and affect tubulin TUBB2A incorporation into microtubules in vivo. We found that variants located in linkage of tubulin dimers could severely affected the function of tubulin TUBB2A, and may lead to more severe clinical phenotypes.
Funding: No Funding