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GeneDx
207 Perry Parkway
Gaithersburg, MD 20877
Phone: 301-519-2100
Fax: 301-519-2892
E-mail: [email protected]
www.genedx.com
Test Information Sheet
EFNB1 Gene Analysis in Craniofrontonasal syndrome
Also known as: CFNS; Craniofrontonasal dysplasia; CFND; Craniofrontonasal dysostosis
Mendelian Inheritance in Man Number: 304110 (CFNS); 300035 (EFNB1 gene)
Clinical features:
Craniofrontonasal syndrome (CFNS) is a rare X-linked dominant disorder characterized by a more severe phenotype of
multiple skeletal malformations in heterozygous females in contrast to no or mild clinical features in hemizygous
males. Females typically display craniofacial asymmetry, marked hypertelorism with a central nasal groove, bifid nasal
tip, coronal craniosynostosis (unilateral or bilateral), corpus callosum agenesis, thick wiry hair, and occasionally cleft
lip and/or palate. Extracranial features include sloping shoulders with dysplastic clavicles, asymmetry of the thoracic
skeleton and pectoral muscle, unilateral breast hypoplasia, longitudinally grooved fingernails, mild cutaneous
syndactyly, and umbilical and diaphragmatic hernia. Hemizygous males have no or only mild manifestations such as
hypertelorism and less frequently cleft lip and/or palate. Males who are mosaic for EFNB1 mutations may present with
a severe phenotype similar to female patients.
Inheritance pattern: X-linked dominant with more severe phenotype in females and under-representation of carrier males
in CFNS families.
Genetics:
CFNS is caused by mutations in the EFNB1 gene located on chromosome Xq13.1. The EFNB1 gene encodes the
transmembrane protein ephrin-B1 which, as part of Eph/ephrin transduction system, controls cell patterning of the
developing skeleton, nervous system, intestine, and blood vessels. The more severe phenotype seen in females has
been hypothesized to occur by the process of random X-inactivation (rather than skewed X-inactivation). As ephrins
are expressed in a spatially and temporally dynamic pattern during embryogenesis, it has been proposed that in
heterozygous females, ephrin-B1-expressing cells and ephrin-B1-deficient cells lead to a disturbance of cell sorting and
migration and subsequent skeletal malformations particularly craniosynostosis. In hemizygous males who have a
homogeneous cell population, it is thought that ephrin-B1 may be replaced by another B-class ephrin. The generally
mild clinical presentation in males suggests that ephrin-B1 is functionally redundant in the majority of tissues in which
it is expressed1,2,3. Regarding the reasons for the observed paucity of carrier males in CFNS families, three contributing
factors have been proposed: (1) predominant paternal origin of de novo EFNB1 mutations, (2) occurrence of somatic
mutations that are expected to occur twice as often in females, and (3) reduced reproductive fitness in affected females.
Reasons for referral:
1. Confirmation of a clinical diagnosis
2. Genetic counseling and risk assessment
3. Prenatal diagnosis in families with a known mutation
Test method:
Analysis is performed by bi-directional sequencing of the coding regions (exons 1-5) and splice sites of the EFNB1
gene. In cases where (1) no small intragenic mutation is identified and (2) no heterozygous positions are observed,
focused array CGH analysis with exon-level resolution (ExonArrayDx) is available for detection of a partial/whole
deletion of one EFNB1 allele. Mutations found in the first person of a family to be tested are confirmed by repeat
analysis using sequencing, restriction fragment analysis, or another appropriate method.
Test sensitivity:
In the largest published study, EFNB1 mutations were identified in 33 out of 38 (86.8%) individuals with clinically
diagnosed CFNS5. Specifically, mutations were detected in 25 of 29 (86.2%) patients with sporadic CFNS and in 8 of 9
(88.9%) families. In two additional studies with a total of 23 families, EFNB1 mutations were found in all clinically
affected individuals1,2. The sequencing approach used by GeneDx will identify >99% of existing small, intragenic
mutations in the EFNB1 gene, however it cannot detect partial or whole gene deletions in affected females. If indicated,
Information Sheet CFNS
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(c) GeneDx 12/2014
focused array CGH analysis with exon-level resolution (ExonArrayDx) is available is available to detect such deletions
or duplications.
Mutation spectrum:
While mutations have been identified in all 5 exons and intron 2 of EFNB1, the majority (52%) are located in exon 2.
Another 20% of mutations have been found in exon 3. Mutation types include frameshift, nonsense, missense, and
splice site. Additionally, heterozygous deletions of the EFNB1 have been described including two partial deletions
(exons 2-5; exons 1-3)1,4, 1 whole deletion of exons 1-54, and three contiguous gene deletions involving EFNB1 and
adjacent genes6. The phenotype associated with EFBN1 deletions has not been observed to be different than that caused
by point mutations. However, two girls with contiguous gene deletions including EFBN1 and four additional genes
(OPHN1, YIPF6, STARD8, PJA1) were observed to have both CFNS and developmental delay6.
Specimen Requirements and Shipping/Handling:
 Blood: A single tube with 1-5 mL whole blood in EDTA. Ship overnight at ambient temperature, using a cool pack
in hot weather. Specimens may be refrigerated for 7 days prior to shipping.
 Buccal Brushes: Can be used as an alternative to blood for EFNB1 sequencing only. Gene deletion/duplication
testing (ExonArrayDx) requires submission of a venous blood sample. When sending a buccal sample, use a
GeneDx buccal kit (others not accepted). Submit by mail. Buccal brushes are not accepted on children under 6
months of age.
 Prenatal Diagnosis: For prenatal testing for a known mutation in the EFNB1 gene, please refer to the specimen
requirements table on our website at: http://www.genedx.com/test-catalog/prenatal/. Ship specimen overnight at
ambient temperature, using a cool pack in hot weather.
Required Forms:
 Sample Submission (Requisition) Form – complete all pages
 Payment Options Form or Institutional Billing Instructions
For test codes, prices, CPT codes, and turn-around-times, please refer to the “Craniofrontonasal syndrome”
page on our website: www.genedx.com
References:
(1) Wieland, I. et al. Mutations of the Ephrin-B1 Gene Cause Craniofrontonasal Syndrome. Am J Hum Genet.
74:1209-1215, 2004. (2) Twigg, S. et al. Mutations of ephrin-B1 (EFNB1), a marker of tissue boundary formation,
cause craniofrontonasal syndrome. PNAS. 101:8652-8657, 2004. (3) Wieland, I. et al. Dissecting the molecular
mechanism in craniofrontonasal syndrome: differential mRNA expression of mutant EFBN1 and the cellular mosaic.
Eur J Hum Genet. 16: 184-191, 2008. (4) Twigg, S. et al. The Origin of EFNB1 Mutations in Craniofrontonasal
Syndrome: Frequent Somatic Mosaicism and Explanation of the Paucity of Carrier Males. Am J Hum Genet. 78:9991010, 2006. (5) Wieland, I. et al. Twenty-Six Novel EFNB1 Mutations in Familial and Sporadic Craniofrontonasal
Syndrome (CFNS) Hum. Mutat. 26:113-118, 2005. (6) Wieland, I. et al. Contiguous gene deletions involving EFNB1,
OPHN1, PJA1 and EDA in patients with craniofrontonasal syndrome. Clin Genet. 72:506-516, 2007. (7) Twigg, S. et
al. Cellular interferences in craniofrontonasal syndrome: males mosaic for mutations in the X-linked EFNB1 gene are
more severely affected than true hemizygotes. Hum Mol Genet 22(8):1654-1662.
Information Sheet CFNS
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(c) GeneDx 12/2014