A mutational hotspot in TUBB2A associated with impaired heterodimer formation and severe brain developmental disorders.

Introduction: Microtubules are essential components of the neuronal cytoskeleton. The α- and β-tubulins, variably expressed in the central nervous system, play key roles in neurogenesis and brain development. Pathogenic variants in TUBB2A have recently been identified as an ultra-rare cause of pediatric neurodevelopmental disorders (NDDs). However, the neurological and behavioral manifestations, genotype-phenotype correlations, and underlying disease mechanisms remain poorly understood due to the limited number of reported families.

Methods: We describe a cohort of families presenting with microcephaly, global developmental delay, speech impairment, seizures and/or EEG abnormalities, movement disorders and severe behavioral disorders. Clinical assessments and brain imaging studies were conducted over a 10-year follow-up period. Genetic analysis was performed via whole-exome sequencing (WES), and structural modeling was used to investigate the functional impact of the identified variants.

Results: WES revealed a novel recurrent heterozygous pathogenic variant in TUBB2A (NM_001069.3:c.1172G > A; NP_001060.1:p.Arg391His), identified as the cause of disease in multiple affected individuals from unrelated families. Comparative analysis with previously reported TUBB2A de novo variants confirmed that this novel recurrent mutation affects a highly conserved Arg391 residue within the longitudinal E-site heterodimer interface. Computational modeling demonstrated that the variant disrupts α/β-tubulin heterodimer formation, impairing binding stability at this critical interaction site.

Discussion: Our findings expand the phenotypic and genotypic spectrum of TUBB2A-related disorders and identify Arg391 as a mutational hotspot linked to severe brain developmental disorders due to aberrant tubulin dynamics, highlighting the disruption of the α/β-tubulin heterodimer formation as the disease mechanism associated to this novel hotspot variant. These results provide new insights into disease mechanisms and offer a foundation for potential future therapeutic approaches aimed at stabilizing α/β-tubulin interactions.