An essential feature of successful mammalian reproduction is the fusion of a sperm with a mature oocyte. We previously found that heterozygous mutations in TUBB8 caused oocyte maturation arrest. In this study, we identified novel heterozygous and homozygous mutations in TUBB8 that cause variability in the corresponding phenotypes of human oocytes and early embryos. For example, oocyte with some mutations can exclude the first polar body and be fertilized, although the ensuing embryos became developmentally arrested. Our data substantially expand the range of dysfunctional oocyte phenotypes incurred by mutation in TUBB8, extend the class of genetic diseases known as the tubulinopathies, and provide new criteria for the qualitative evaluation of MII oocytes for IVF. (By Dr. Lei Wang, http://jmg.bmj.com/content/early/2016/06/06/jmedgenet-2016-103891 )