Consistent with these striking findings, mutations in the human EFNB1 gene have been identified as the cause of Craniofrontonasal syndrome (CFNS), a human X-linked disease that has been very puzzling for geneticists because it involves patterning defects in heterozygous female carriers but not their hemizygous fathers103,104. This evidence concerns the gene EFNB1 and Craniofrontonasal dysplasia.