Novel variants in TUBB8 gene cause multiple phenotypic abnormalities in human oocytes and early embryos

The genotype-phenotype relationships between TUBB8 variants and female infertility are difficult to clearly define due to the complex inheritance patterns and the highly heterogeneous phenotypes. This study aims to identify novel TUBB8 variants and relevant phenotypes in more infertile females.

A total of 35 females with primary infertility were recruited from two reproductive centers and investigated for identifying variants in TUBB8. Pedigree analysis, in-silico analysis and molecular remodeling were performed to assess their clinical significance. The effects of the variants on human oocytes and embryos as well as HeLa cells were analyzed by morphological observations, immunostaining and Western blot.

We totally identified five novel variants (p.G13R, p.Y50C, p.T136I, p.F265V and p.T366A) and five previously reported variants (p.I4L, p.L42V, p.Q134*, p.V255M and p.V349I) in TUBB8 from 9 unrelated females with primary infertility. These variants were rare and highly conserved among different species, and were inherited in autosomal dominant/recessive patterns, or occurred de novo. In vitro functional assays in HeLa cells revealed that exogenous expression of mutant TUBB8 proteins caused different degrees of microtubule structural disruption. The existence of these pathogenic TUBB8 variants finally induced oocyte maturation arrest or morphological abnormalities, fertilization failure, cleavage failure, embryonic development defects and implantation failure in the affected females.

These findings enriched the variant spectrum of TUBB8 gene and could contribute to optimize genetic counselling and clinical management of females with primary infertility.