Craniofrontonasal syndrome (CFNS [MIM 304110]) is an X-linked malformation syndrome characterized by craniofrontonasal dysplasia and extracranial manifestations in heterozygous females.
Upon clonal expansion of patient cells with either the wild-type or mutant EFNB1 on the active X-chromosome, we were able to separate mutant and wild-type EFNB1-expressing cells in vitro, further supporting the concept of cellular interference in CFNS.
Although EFNB1 is X-inactivated, we did not observe markedly skewed X-inactivation in either blood or cranial periosteum from females with CFNS, indicating that lack of ephrin-B1 does not compromise cell viability in these tissues.
Hence, we propose that X-linked cases resembling Teebi hypertelorism may have a similar mechanism to CFNS, and that cellular mosaicism for different levels of ephrin-B1 (as well as simple presence/absence) leads to craniofacial abnormalities.
Here, by generating hiPSCs from CFNS patients, we demonstrate that mosaicism for EPHRIN-B1 expression induced by random X inactivation in heterozygous females results in robust cell segregation in human neuroepithelial cells, thus supplying experimental evidence that Eph/ephrin-mediated cell segregation is relevant to pathogenesis in human CFNS patients.
Although EFNB1 is X-inactivated, we did not observe markedly skewed X-inactivation in either blood or cranial periosteum from females with CFNS, indicating that lack of ephrin-B1 does not compromise cell viability in these tissues.