Novel heterozygous truncating variant in TUBB associated with thrombocytopaenia and neurological abnormalities

Abstract

Tubulinopathies constitute a growing and heterogeneous class of disorders caused by pathogenic variants in genes encoding for tubulins, the structural components of microtubules. These conditions encompass a broad spectrum of neurological manifestations, most commonly including structural brain malformations and, less frequently, neurodegenerative disorders. In addition to brain diseases, tubulinopathies also include non-neurological conditions, such as female meiotic infertility and bleeding disorders. Among tubulin genes, TUBB , encoding the class I β-tubulin, has been associated with a wide range of clinical conditions, primarily including neurodevelopmental delay, structural brain abnormalities, and skin creases. More recently, TUBB has also been linked to inherited macrothrombocytopaenia, suggesting a broader, yet still incompletely defined, role of this β-tubulin in haematopoiesis and platelet biogenesis. In this study, we aim to investigate pathogenic mechanisms of a novel frameshift variant in TUBB (c.628dup; p.Ile210AsnfsTer40), identified in a subject affected by thrombocytopaenia and neurological involvement. Functional analyses demonstrated that the p.Ile210AsnfsTer40 TUBB mutation leads to the production of a truncated β-tubulin with reduced protein stability and aberrant subcellular localization. The mutant protein showed impaired interaction with α-tubulin and kinesin family member 1 A (KIF1A), suggesting defective microtubule assembly and microtubule-mediated intracellular transport. Furthermore, the inhibition of the proteasome degradative pathway resulted in a marked increase of the mutant TUBB, indicating altered proteostasis and enhanced degradation of the truncated tubulin. Finally, we showed that the p.Asp249Val substitution in TUBB , previously associated with macrothrombocytopaenia, similarly reduces protein stability, weakens interaction with α-tubulin, and impairs TUBB incorporation into microtubules. This study associates the novel heterozygous truncating p.Ile210AsnfsTer40 variant in TUBB with a multisystem disorder characterized by haematological and neurological manifestations, expanding the phenotypic spectrum of TUBB -related diseases. Our findings indicate that reduced protein stability and functional impairment of β-tubulin represent key pathogenic mechanisms underlying this condition. Lastly, our experimental evidence further supports the implication of TUBB dysfunctions in haematological abnormalities, offering additional insight into the molecular basis and clinical variability of tubulin-related disorders.