Home
HelpTest Code LAB1856 Hereditary Hemorrhagic Telangiectasia Sequencing
Clinical System Name
Hereditary Hemorrhagic Telangiectasia Sequencing
Description
Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular disorder affecting 1 in 5,000-10,000 individuals. HHT is characterized by telangiectasias (often on the face, lips, and hands, and in oral, nasal, and gastrointestinal (GI) mucosa), recurrent spontaneous nosebleeds (epistaxis), and arteriovenous malformations (AVMs) of the lungs, liver, and brain. Symptoms of HHT are age-dependent and are not typically present at birth, with average onset in teens to 20’s. Mutations in 5 genes (ACVRL1, ENG, GDF2, RASA1, and SMAD4) have been associated with HHT, and pathogenic variants in these genes are found in approximately 90% of individuals with HHT. Most individuals with HHT have an affected parent, although individuals with de novo and post-zygotic somatic mutations have been reported.
Capillary malformation- arteriovenous malformation syndrome (CM-AVM) is a vascular disorder estimated to affect 1 in 100,000 individuals. It is characterized by the presence of multiple capillary malformations and, in approximately one-third of individuals, fast-flow arteriovenous malformations that can be life-threatening. AVMs are typically present at birth in individuals with CM-AVM syndrome, though they may not be symptomatic. The capillary malformations may increase over time. Mutations in two genes (RASA1 and EPHB4) have been associated with CM-AVM, and pathogenic variants in these genes are found in approximately 75% of individuals with CM-AVM. About 70% of individuals with CM-AVM have an affected parent, with approximately 30% having a de novo pathogenic variant.
Although HHT and CM-AVM can be distinguished clinically, there can be considerable overlap. Both disorders feature AVMs as a primary symptom, and capillary malformations and telangiectasias can be confused. For this reason, we offer HHT and CM-AVM as a single panel of genes with different options for custom HHT testing.
- Hereditary hemorrhagic telangiectasia (HHT) Sequencing Panel (6 genes):
A 6 gene panel which includes ACVRL1, ENG, GDF2, SMAD4, RASA1, and EPHB4. Pathogenic sequencing variants in these genes account for approximately 90% of individuals with HHT, and 75% of individuals with CM-AVM.
Please contact LabGC@seattlechildrens.org if you would like to order reflexive testing after the original testing report has been issued.
Sample Requirements
Note: For patients who have had a whole blood transfusion, wait 10 days post transfusion to draw for genetic testing. No wait time is necessary for blood or saliva collection if the patient received leuko-reduced red cells or plasma.
Specimen: Whole blood
Container(s): Lavender/EDTA
Preferred Vol: 3 mL
Minimum Vol: 1 mL
Note: Heparin samples (Green tops) are unacceptable.
Specimen: Saliva collected using Oragene Dx OGD-575/675 collection kit.
Container: Oragene Dx OGD-575/675 collection kit
IMPORTANT NOTE: Manufacturer instructions must be followed. The Oragene Dx OGD575/675 kit is not for children under 6 months. Contact the lab directly for more information or to obtain a kit - 206-987-2617
Specimen: Extracted DNA (MUST specify source on requisition)
Preferred: 5 mcg
Minimum: 2 mcg
Note: Isolation of nucleic acids for clinical testing must be performed in a CLIA-certified
laboratory or a laboratory meeting equivalent requirements as determined by the CAP
and/or the CMS. DNA concentration minimum 50 µg/mL; 260/280 ratio 1.70-2.00.
Processing Instructions
Reject due to: Heparin
Spin: No
Aliquot: No
Temp: 2 - 8 C
Storage location: Molecular Genetics box in CPA refrigerator #2
Off-site collection: Refrigerate blood samples until ready to ship. Transport all sample types at room temperature via overnight shipping.
Stability
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole blood, extracted DNA | RT | 3-5 d |
| Whole blood, extracted DNA | 2 - 8 C |
7 d |
|
Saliva, extracted from ORAgene Dx OGD-575/675 |
Room temperature or refrigerated | up to 2 weeks |
| Extracted DNA | -20 C or -70 C | years |
Note: Whole blood samples > 7days may be submitted to be assessed by our lab for acceptability for testing.
Availability
| STAT | Performed | TAT |
|---|---|---|
| Contact lab | Monday - Friday | 4-8 weeks |
Performing Laboratory
Seattle Children's Laboratory
Department
Department: Molecular Genetics Laboratory
Phone: 206-987-3872
Lab Client Services: 206-987-2617
Lab Genetic Counselor: LabGC@seattlechildrens.org
CPT Codes
81479
Methodology
Method: Next Generation Sequencing technology using an Illumina NextSeq instrument. Target region includes coding exons and a minimum of 10 bp of flanking intron boundaries of the genes tested. Target enrichment performed using a custom Integrated DNA Technologies (IDT) Exome Hyb Panel v2.
Average coverage >100x, depth of coverage for all target regions is at least 20x.
Reported gene set:
HHT Sequencing Panel (6 genes): ACVRL1, ENG, GDF2, SMAD4, RASA1, and EPHB4
Limitations:
This testing is performed on an exome backbone with analysis restricted to the panel genes. This method can detect single nucleotide variants (SNVs), small deletions, small insertions, and copy number variants in the regions targeted. Some regions cannot be efficiently captured due to sequence homology or sequence properties. This method will not detect large insertions and deletions, complex indels, structural variants (e.g. inversions, translocations), short tandem repeats, or other complex variants. Variants located outside of targeted regions will not be detected.
Based on validation studies, the bioinformatics pipeline showed precision and detection >99% for SNVs in regions with coverage greater than 20x and high mapping quality. Sensitivity for CNVs involving multiple genes is >99% and sensitivity for intragenic CNVs is >90%. Mosaic sequence variants present at <25% allele frequency may not be reliably detected, and detection sensitivity is dependent on the nature of the variant. The sensitivity of detection of mosaic copy number variants has not been evaluated.
Reference Range
Interpretive report will be provided. Variants are not reported if they are considered benign.
Clinical Utility
The diagnosis of HHT is established in an individual with three or more of the following clinical features:
- spontaneous and recurrent epistaxis
- multiple telangiectases at characteristic sites including the face, lips, oral cavity and fingers
- visceral AVM (pulmonary, cerebral, hepatic, spinal) or gastrointestinal telangiectases (with or without bleeding)
- a family history of HHT
Approximately 90% of individuals with HHT will have a pathogenic sequencing variant identified in one of these five genes: ACVRL1, ENG, GDF2, RASA1, and SMAD4. The use of deletion/duplication analysis increases the detection rate by approximately 10%.
Identification of a heterozygous pathogenic variant in ACVRL1, ENG, GDF2, or SMAD4 establishes the diagnosis if clinical features are inconclusive. Pathogenic variants in RASA1 and EPHB4 have been identified in individuals with clinical features that overlap HHT. Timely identification of the genetic cause of HHT or CM-AVM can aid clinicians in making an accurate diagnosis and direct clinical management.
Requisition
Special Instructions
Link to: HHT GeneReviews; RASA1-Related Disorders GeneReviews
Other References:
- Wooderchak-Donahue WL et al. Phenotype of CM-AVM2 caused by variants in EPHB4: how much overlap with hereditary hemorrhagic telangiectasia (HHT)? Genet Med. 2019 Feb 14, PMID: 30760892.
- Revencu N et al. RASA1 mosaic mutations in patients with capillary malformation-arteriovenous malformation. J Med Genet. 2019 Jul 12, PMID: 31300548.
- Amyere M et al. Germline Loss-of-Function Mutations in EPHB4 Cause a Second Form of Capillary Malformation-Arteriovenous Malformation (CM-AVM2) Deregulating RAS-MAPK Signaling. Circulation. 2017 Sep 12;136(11):1037-1048, PMID: 28687708.