Phenotypic variability in two female siblings with oocyte maturation arrest due to a TUBB8 variant.

Tubulin beta-8 (TUBB8) is expressed exclusively in the oocyte and early embryo, encoding a beta-tubulin polypeptide that participates in the assembly of microtubules. TUBB8 was first attributed to being responsible for oocyte MI arrest. Further studies have demonstrated that patients with different pathogenic variants have variable phenotypes. We report a TUBB8 variant (c.10 A > C) in two siblings who presented different clinical features of primary infertility. The younger sister showed severe oocyte maturation arrest with abnormal morphology, whereas a few mature oocytes and zygotes could be retrieved from the older sister, but no embryo was available for transfer. This variant was previously reported without in vitro functional assays. In the present study, RT‒qPCR and western blot analyses revealed that c.10 A > C reduces TUBB8 mRNA and protein levels; however, immunofluorescence demonstrated that this variant does not change the localization of the protein. These findings confirm the pathogenicity of the c.10 A > C variant and support the relationship between the variant and phenotype in the patients.