TTC21A and fibrous dysplasia: MMAF, also termed dysplasia of fibrous sheath (DFS) (Chemes et al., 1987), is a type of dysfunction in flagellogenesis that has been reported to be related to several genes, such as DNAH1 (Ben Khelifa et al., 2014), CFAP43, CFAP44 (Tang et al., 2017), TTC21A (Liu W. et al., 2019), TTC29 (Liu C. et al., 2019), etc. Here, using WES on a cohort of 32patientswith MMAF, we identified a novel splicing mutation in CFAP251. Prior to our study, two splicing mutations in CFAP251 (c.2862+1G>A;c.1286 + 2 T > C) were reported (Kherraf et al., 2018; Li et al., 2019).