Craniofrontonasal syndrome (CFNS) is an X-linked disorder characterized by a more severe manifestation in heterozygous females than in hemizygous males. Heterozygous females have
craniofrontonasal dysplasia (CFND) and occasionally extracranial manifestations including midline defects and skeletal abnormalities, whereas hemizygous males show no or only mild features such as
hypertelorism and rarely show
cleft lip or palate. Mutations in the
EFNB1 gene in Xq12 are responsible for familial and sporadic CFNS. The
EFNB1 gene encodes
ephrin-B1, a transmembrane
ligand that also exhibits receptor-like effects. We performed mutation analysis in nine unrelated families and 29 sporadic patients with CFNS.
DNA sequencing revealed mutations in 33 (86.8%) cases including 26 distinct novel mutations. A recurrent
nonsense mutation, c.196C>T/R66X, was detected in one family and four sporadic patients. The majority of mutations (26/33) were located in exons 2 and 3 of the
EFNB1 gene encoding the extracellular
ephrin domain. The mutation spectrum includes frameshift, nonsense, missense, and splice site mutations, with a predominance of frameshift and
nonsense mutations resulting in premature truncation
codons. For the first time we describe mutations in exons 4 and 5 of
EFNB1. Of particular interest are the frameshift mutations located in the last 25
codons of
EFNB1 encoding the carboxyterminal end of
ephrin-B1. They result in an extension by 44 residues. These mutations disrupt the intracellular binding sites for Grb4 and PDZ-effector
proteins involved in reverse signaling. We conclude that the major causes of familial as well as sporadic CFNS are loss of function mutations in the
EFNB1 gene that comprise premature termination or abrogate receptor-
ligand interaction, oligomerization, and
ephrin-B1 reverse signaling.