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EFNB1
ephrin B1
The EFNB1 gene encodes the ephrin B1 protein, vital for cell-to-cell communication and proper tissue development, with clinical implications in conditions like craniofrontonasal dysplasia. The EFNB1 gene provides the blueprint for the ephrin B1 protein, a transmembrane protein involved in crucial cell signalling pathways.
EFNB1 is located on the long (q) arm of chromosome X, at band Xq13.1. Arm ratio per GRCh38 - banding schematic.
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Overview
The EFNB1 gene, also known by synonyms such as EFL3 or EPLG2, contains the genetic instructions for producing the ephrin B1 protein. This protein is fundamentally involved in cellular communication, acting as a ligand that binds to specific receptor proteins on neighbouring cells. This interaction is essential for guiding the correct development and patterning of various tissues and organs during embryonic growth.
Located on the X chromosome, EFNB1 plays a key role in processes like cell adhesion and the organisation of cells into complex structures. Pathogenic variants in this gene are associated with craniofrontonasal dysplasia, highlighting its importance in human development.
What the gene does
The ephrin B1 protein, encoded by the EFNB1 gene, is a transmembrane protein. This means it spans the cell membrane, with a portion extending outside the cell and another within. The extracellular part of ephrin B1 interacts with specific Eph receptor kinases located on the surface of adjacent cells. This binding creates Eph/ephrin complexes, which are critical for cell adhesion and the transmission of signals between cells.
This cell-to-cell communication is particularly important for the normal patterning and shaping of numerous tissues and organs during prenatal development. In the brain, Eph/ephrin complexes contribute to the maturation of nerve cells, known as neurons, and also influence synaptic plasticity. Synaptic plasticity refers to the ability of the connections between neurons to change and adapt in response to experience, an important aspect of learning and memory.
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Chromosome location
The EFNB1 gene is situated on the X chromosome at position Xq13.1. This specific location refers to the long arm (q) of the X chromosome, within region 1, band 3, and sub-band 1. As an X-linked gene, its inheritance pattern differs between males and females, influencing the presentation of associated conditions. The EFNB1 gene contains multiple exons, which are segments of DNA that contain protein-coding information.
Protein structure
The ephrin B1 protein is composed of 346 amino acids. Its structural organisation includes several functional regions and motifs. An important component is the Ephrin RBD (Receptor Binding Domain), located between amino acids 30 and 164, which is responsible for binding to Eph receptor kinases. A Disordered region, spanning amino acids 169-228, suggests flexibility and potential for various protein interactions.
Further functional elements include a Nuclear localisation signal (NLS) between amino acids 260 and 273, which may direct the protein or an associated complex to the cell nucleus. The protein also features a region involved in Interaction with ZHX2, from amino acids 263-294. Lastly, a PDZ-binding motif is found at amino acids 344-346, often implicated in localising proteins at specific membrane sites and organising signalling complexes.
Key variants
Genetic variants within the EFNB1 gene can alter the function of the ephrin B1 protein, ranging from subtle modifications to significant disruptions. These changes can result in an improperly formed or non-functional protein, impairing its role in cell communication and tissue development. Over 115 different pathogenic variants in the EFNB1 gene have been identified as causative for craniofrontonasal dysplasia. These variants include various types of alterations, such as point mutations, deletions, and insertions, each with the potential to impact protein expression or function. The severity and presentation of associated conditions can vary depending on the specific variant and its effect on protein activity.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.101_114del | p.Pro34fs | Pathogenic/Likely pathogenic | ★★☆☆ | Craniofrontonasal syndrome |
c.161C>T | p.Pro54Leu | Pathogenic/Likely pathogenic | ★★☆☆ | Craniofrontonasal syndrome |
c.196C>T | p.Arg66Ter | Pathogenic | ★★☆☆ | Craniofrontonasal syndrome |
c.1A>G | p.Met1Val | Pathogenic | ★★☆☆ | Craniofrontonasal syndrome |
c.253C>T | p.Gln85Ter | Pathogenic | ★★☆☆ | Craniofrontonasal syndrome |
c.30C>T | p.Gly10= | Pathogenic | ★★☆☆ | not provided |
c.35G>A | p.Trp12Ter | Pathogenic/Likely pathogenic | ★★☆☆ | EFNB1-related disorder |
c.451G>A | p.Gly151Ser | Pathogenic | ★★☆☆ | EFNB1-related disorders |
c.472A>G | p.Met158Val | Pathogenic/Likely pathogenic | ★★☆☆ | not provided |
c.499+1G>A | - | Pathogenic/Likely pathogenic | ★★☆☆ | Craniofrontonasal syndrome |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the EFNB1 gene are principally associated with craniofrontonasal dysplasia, an X-linked inherited condition. This condition typically involves abnormalities affecting the skull and facial bones due to the premature fusion of cranial sutures (craniosynostosis). The condition commonly presents with distinct facial features and may also involve other skeletal anomalies. Although X-linked, females often experience more pronounced symptoms than affected males, presenting a unique inheritance pattern related to X-chromosome inactivation.
Inheritance pattern
Conditions caused by pathogenic EFNB1 variants typically follow x-linked dominant inheritance.
X-linked dominant: all daughters of an affected father inherit the altered X and are affected. Sons receive the father's Y and are unaffected.
UK clinical status
In the UK, the EFNB1 gene is included in several NHS Genomic Medicine Service national test panels, indicating its clinical significance. It is classified as 'green' on the Clefting panel, Common craniosynostosis syndromes panel (R99), DDG2P panel, Foetal anomalies panel (R21), and the Rare syndromic craniosynostosis or isolated multisuture synostosis panel (R100). This 'green' status confirms there is sufficient evidence for routine testing of this gene within these clinical contexts.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Currently, there is no specific evidence to suggest that particular lifestyle choices can prevent or directly mitigate the effects of conditions caused by EFNB1 gene variants. Maintaining a generally healthy lifestyle-including a balanced diet, regular physical activity, and avoiding smoking-is widely recommended for overall well-being. However, these general health practices are not known to alter the genetic predisposition or clinical manifestation of inherited conditions linked to EFNB1.
Supplement considerations
There is no conclusive scientific evidence to support the use of any specific dietary supplements for preventing or treating conditions associated with EFNB1 gene variants. Individuals considering supplements for any health concern should consult a healthcare professional. the efficacy and safety of supplements are not consistently regulated, and claims of benefit often lack rigorous scientific backing.
Frequently asked questions
What is the primary function of the EFNB1 gene?
The EFNB1 gene provides instructions for the ephrin B1 protein, which is crucial for cell-to-cell communication and adhesion. This communication is vital for the normal patterning and shaping of many tissues and organs during development.
What condition is primarily associated with EFNB1 gene variants?
Pathogenic variants in the EFNB1 gene are primarily associated with craniofrontonasal dysplasia. This condition involves the premature fusion of skull bones (craniosynostosis) and distinct facial features.
Why do females often have more severe symptoms of craniofrontonasal dysplasia?
Although EFNB1 is an X-linked gene, females with craniofrontonasal dysplasia often have more severe symptoms due to the complex process of X-chromosome inactivation, which can lead to a mosaic pattern of affected cells.
How does the ephrin B1 protein interact with other cells?
The ephrin B1 protein, located on the surface of one cell, binds to Eph receptor kinases on the surface of a neighbouring cell. This interaction forms Eph/ephrin complexes that facilitate cell adhesion and signal transmission.
Is the EFNB1 gene included in UK NHS genetic testing panels?
Yes, the EFNB1 gene is included in several UK NHS Genomic Medicine Service national test panels, including those for Clefting, Craniosynostosis syndromes, Foetal anomalies, and DDG2P, indicating its established clinical relevance.
References
- Niethamer TK, Larson AR, O'Neill AK. EPHRIN-B1 Mosaicism Drives Cell Segregation in Craniofrontonasal Syndrome hiPSC-Derived Neuroepithelial Cells. Stem cell reports. 2017. PMID: 28238796
- Zhang RX, Han Y, Chen C. EphB2 in the Medial Prefrontal Cortex Regulates Vulnerability to Stress. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology. 2016. PMID: 27103064
- van den Elzen ME, Twigg SR, Goos JA. Phenotypes of craniofrontonasal syndrome in patients with a pathogenic mutation in EFNB1. European journal of human genetics : EJHG. 2014. PMID: 24281372