ENG Mutation (VUS): Clinical Significance and Management
An ENG variant of uncertain significance (VUS) is a genetic change in the endoglin gene where current evidence is insufficient to determine whether it causes Hereditary Hemorrhagic Telangiectasia (HHT), requiring clinical diagnosis based on Curaçao criteria rather than genetic results alone.
Understanding ENG and HHT
The ENG gene encodes endoglin, a protein critical for proper arterial development and remodeling. Pathogenic mutations in ENG cause HHT type 1, an autosomal dominant vascular disorder affecting approximately 1 in 5000 individuals 1. In 97% of patients with definite clinical HHT diagnosis, causative mutations are identified in ENG, ACVRL1, or SMAD4 genes 1.
What a VUS Means in Practice
A VUS does NOT confirm or rule out HHT. The majority of VUSs ultimately prove to be benign when later reassessed, though resolution of uncertainty is rarely timely 2. This creates several clinical challenges:
- Diagnostic uncertainty that complicates clinical decision-making
- Potential for unnecessary treatment and adverse psychological effects 2
- Time-consuming analysis required for interpretation
- Family implications that remain unclear until variant is reclassified
Clinical Approach to ENG VUS
Rely on Clinical Diagnosis, Not Genetics
Use the Curaçao criteria to establish HHT diagnosis clinically 1:
- Spontaneous recurrent epistaxis
- Multiple telangiectases at characteristic sites (lips, oral cavity, fingers, nose)
- Visceral arteriovenous malformations (pulmonary, hepatic, cerebral, spinal)
- First-degree relative with HHT
Definite diagnosis requires 3 or more criteria; possible diagnosis requires 2 criteria 1.
Screening and Management Strategy
If clinical suspicion for HHT exists (2+ Curaçao criteria), proceed with organ screening regardless of VUS status:
- Pulmonary AVM screening - essential to prevent stroke and brain abscess
- Cerebral AVM screening - particularly in pediatric patients
- Hepatic involvement assessment - evaluate for liver vascular malformations
- GI bleeding surveillance - monitor for anemia and iron deficiency 1
Family Evaluation
Perform family-based segregation analysis - test affected and unaffected family members to determine if the VUS tracks with disease 2. This is one of the most powerful tools for reclassifying VUSs:
- If the variant segregates with clinically affected individuals, it strengthens pathogenicity
- If unaffected family members carry the variant, it suggests benign nature
- This approach can accelerate variant reclassification
Examples of Pathogenic ENG Variants
Recent research demonstrates various pathogenic ENG mutations 3, 4, 5:
- Frameshift mutations causing premature termination (c.613del, c.1498dup, c.322del)
- Splice-site variants causing aberrant mRNA splicing (c.1428+2T>C)
- Signal peptide mutations impairing protein processing (c.38T>A, p.Leu13Gln)
- Missense variants disrupting protein structure (Ala218Val predicted likely pathogenic) 6
These examples illustrate that definitively pathogenic variants typically cause loss of function through protein truncation, impaired processing, or disrupted cellular localization.
Critical Pitfalls to Avoid
Do not withhold HHT screening based on a VUS result. The clinical consequences of missing pulmonary or cerebral AVMs are severe (stroke, brain abscess, hemorrhage), while the harm of screening is minimal 1.
Do not assume a VUS is pathogenic and subject patients to unnecessary anxiety or interventions without clinical evidence of disease 2.
Do not rely solely on genetic testing for asymptomatic family members with a VUS - genetic testing is most useful when a definitively pathogenic variant has been identified in the family 1.
Ongoing Monitoring
For patients with VUS results:
- Recontact the testing laboratory periodically (annually) to check for variant reclassification
- Maintain clinical surveillance based on phenotype, not genotype
- Document family history changes that might inform variant interpretation
- Consider research participation in variant interpretation consortia
The presence of a VUS should trigger clinical evaluation and phenotype-based management, not genetic-based assumptions about disease status.