The most well defined example of this is the craniofrontonasal syndrome, caused by a deficiency of Ephrin-B1 (EFNB1).20 Other members of the ephrin family of proteins can substitute for a deficiency of EFNB1 in males with the deleterious variant, and as a result, they have minimal clinical symptoms. This evidence concerns the gene EFNB1 and Craniofrontonasal dysplasia.