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

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

Genetic screening and analysis of TUBB8 variants in females seeking ART.

RESEARCH QUESTION: More than 100 variants have been identified in the TUBB8 gene, which account for approximately 30% of infertile women with oocyte maturation defects. But what is the correlation between the highly phenotypic diversity and genetic variability? Are there other variants in TUBB8 related to female infertility? DESIGN: TUBB8 resequencing was performed in 80 female subjects who were experiencing infertility and were seeking treatment with assisted reproductive technologies (ART), or had ever experienced ART failure due to oocyte maturation defects. All variants were evaluated with pedigree analysis, population frequency, in-silico analysis and molecular modelling. The effects of the variants on oocytes/arrested embryos were assessed by morphological observations, immunostaining, embryo biopsies and chromosome euploidy analysis. RESULTS: Nine missense variants and two frameshift variants from an additional 15 families were identified, including four novel variants and seven previously reported recurrent variants. These TUBB8 variants were related to highly variable phenotypes, including abnormalities in oocyte maturation or morphology, fertilization failure, embryonic development abnormalities and implantation failure. Also further clarified were the incomplete penetrance of heterozygous p.E108K, the likely benign significance of heterozygous p.A313V and the clinical effect of a novel variant of p.R380C. CONCLUSIONS: This study significantly expands the variant spectrum of the TUBB8 gene and, together with the available findings on TUBB8 variants and female infertility, will potentially facilitate the genetic counselling of infertile women in future.

Characterization of primary female infertility in a Nigerian tertiary hospital: A case-control study.

Primary female infertility is a serious reproductive health concern amongst many women in Nigeria with associated psychosocial impact. There is a need for early prediction of this disorder for increased chances of fertility in Nigerian women. This study reported the anthropometric, sociodemographic, and clinical baseline characteristics of primary infertility females and studied their viability as predictors of primary infertility. This is a case-control study of primarily infertile (54) and fertile (50) Nigerian females aged 20-44 years recruited by random selection of patients who visited University College Hospital between August and November 2020. A clinical proforma was utilized to assess sociodemographic data, fertility history and clinical diagnosis of study participants. The body mass index (BMI) of both fertile and infertile females was in the overweight category (27.98±0.87 and 28.18±0.59, respectively). Both fertile and primary infertile females present a normal menarcheal age (13.68±0.27 and 13.91 ± 0.32 years, respectively), and there was no significant difference between the menarcheal age (p = 0.411) in both study groups. Ovarian disorder was the most contributing clinical diagnosis (67%) of primary infertility. There is a significant strong association between menarcheal age, ovarian factor infertility (χ2 = 13.839, φc = 0.458, p = 0.008) and tubal factor infertility (χ2 = 11.111; φc = 0.527, p=0.025). Females with primary infertility may present with overweight in no significantly different way than fertile females and BMI may not be useful in predicting primary infertility. However, menarcheal age may be a valuable tool to predict the ovarian and tubal factors in primary infertility.