The EFNB1 gene is located on the X chromosome and loss-of-function variants in the EFNB1 gene are assumed to cause craniofrontonasal syndrome through a paradoxical gender reversal in severity, where females usually develop typical features of craniofrontonasal syndrome and males usually have hypertelorism as the only feature. This evidence concerns the gene EFNB1 and Craniofrontonasal dysplasia.