Test ID: HHTP
Hereditary Hemorrhagic Telangiectasia, ENG and ACVRL1 Full Gene Analysis

Aiding in the diagnosis of hereditary hemorrhagic telangiectasia (HHT), types 1 and 2

• Informed Consent for Genetic Testing
• Hereditary Hemorrhagic Telangiectasia (HHT) Gene Testing Patient Information Sheet
• Multiple Cardiovascular-Related Gene Sequencing Tests

Polymerase Chain Reaction (PCR) Followed by DNA Sequence Analysis and Dosage Analysis by Multiplex Ligation-Dependent Probe Amplification (MLPA)

(PCR is utilized pursuant to a license agreement with Roche Molecular Systems, Inc.)

Multiple cardiovascular-related gene sequencing tests can be performed on a single specimen after a single extraction. See Multiple Cardiovascular-Related Gene Sequencing Tests in Special Instructions for a list of tests that can be ordered together.

Container/Tube: Lavender top (EDTA)       

Specimen Volume: 3 mL

Collection Instructions: Send specimen in original tube.

Additional Information:

1. Include physician name and phone number with the specimen.
2. Transfusions will interfere with testing for up to 4 to 6 weeks. DNA obtained from white cells may not provide useful information for patients who received a recent transfusion of blood that was not leukocyte-reduced. Wait 4 to 6 weeks until transfused cells have left the patient's circulation before drawing the patient's blood specimen for genotype testing.

Forms:

1. Hereditary Hemorrhagic Telangiectasia (HHT) Gene Testing Patient Information Sheet (Supply T650) in Special Instructions

2. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.

Hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome, is an autosomal dominant vascular dysplasia characterized by the presence of arteriovenous malformations (AVMs) of the skin, mucosa, and viscera. Small AVMs, or telangiectasias, develop predominantly on the face, oral cavity, and/or hands, and spontaneous, recurrent epistaxis (nosebleeding) is a common presenting sign. Symptomatic telangiectasias occur in the gastrointestinal tract of about 30% of HHT patients. Additional serious complications associated with HHT include transient ischemic attacks, embolic stroke, heart failure, cerebral abscess, massive hemoptysis, massive hemothorax, seizure, and cerebral hemorrhage. These complications are a result of larger AVMs, which are most commonly pulmonary, hepatic, or cerebral in origin, and occur in approximately 30%, 40%, and 10% of individuals with HHT, respectively.

HHT is inherited in an autosomal dominant manner; most individuals have an affected parent. HHT occurs with wide ethnic and geographic distribution, and is significantly more frequent than formerly thought. It is most common in Caucasians, but it occasionally occurs in Asians, Africans, and individuals of Middle Eastern descent. The overall incidence of HHT in North America is estimated to be between 1:5,000 and 1:10,000. Penetrance seems to be age related, with increased manifestations occurring over one’s lifetime. For example, approximately 50% of diagnosed individuals report having nosebleeds by age 10 years, and 80% to 90% by age 21 years. As many as 90% to 95% of affected individuals eventually develop recurrent epistaxis.

Two genes are most commonly associated with HHT: the endoglin gene (ENG), containing 15 exons and located on chromosome 9 at  band q34; and the activin A receptor, type II-like 1 gene (ACVRL1 or ALK1), containing 10 exons and located on chromosome 12 at band q1. Mutations in these genes occur in about 80% of individuals with HHT. ENG and ACVRL1 encode for membrane glycoproteins involved in transforming growth factor-beta signaling related to vascular integrity. Mutations in ENG are associated with HHT type 1 (HHT1), which has been reported to have a higher incidence of pulmonary AVMs, whereas ACVRL1 mutations occur in HHT type 2 (HHT2), which has been reported to have a higher incidence of hepatic AVMs. It has been suggested that HHT1 has a more severe phenotype compared to HHT2.

The majority of mutations in ENG and ACVRL1 are point mutations, which are detectable by sequencing. Sequencing of ENG and ACVRL1 provides for a detection rate of approximately 60% to 80% of mutations involved in HHT. Approximately 10% of ENG and ACVRL1 mutations are large genomic deletions and duplications (also known as dosage alterations), which are not detectable by sequencing, but are detectable by methods such as multiplex ligation-dependent probe amplification (MLPA).

HHT is phenotypically heterogeneous both between families and amongst affected members of the same family. Furthermore, complications associated with HHT have variable ranges of age of onset. Thus, HHT can be diagnostically challenging. Genetic testing for ENG and ACVRL1 mutations allows for the confirmation of a suspected genetic disease. Confirmation of HHT diagnosis will allow for proper treatment and management of the disease, preconception/prenatal counseling, and family counseling. In addition, it has been estimated that genetic screening of suspected HHT individuals and their families is more economically effective than conventional clinical screening.(1)

An interpretive report will be provided.

An interpretive report will be provided.

Absence of a mutation does not preclude the diagnosis of hereditary hemorrhagic telangiectasia (HHT) unless a specific mutation has already been identified in an affected family member. Mutations in ACVRL1 and ENG occur in approximately 80% of individuals with clinically-defined HHT.

This method will not detect mutations that occur deep in the introns and in the regulatory regions of the gene.  

Sometimes a genetic alteration of unknown significance may be identified. In this case, testing of appropriate family members may be useful to determine pathogenicity of the alteration.

Any error in the diagnosis or in the pedigree provided to us, including false-paternity, could lead to erroneous interpretation of results.

Rare, undocumented polymorphisms may be present which could lead to false-negative or false-positive results.

Once a mutation has been identified in a family, targeted mutation analysis can be performed in at-risk family members:

-ENGK/89391 Hereditary Hemorrhagic Telangiectasia, ENG Gene, Known Mutation

-ACVK/89393 Hereditary Hemorrhagic Telangiectasia, ACVRL1 Gene, Known Mutation

Or if a duplication or deletion is identified:

-HHTM/89587 Hereditary Hemorrhagic Telangiectasia, ENG and ACVRL1 Large Deletion/Duplication, Molecular Analysis

1. Cohen J, Faughnan ME, Letarte M, et al: Cost comparison of genetic and clinical screening in families with hereditary hemorrhagic telangiectasia. Am J of Med Genet A 2005 Aug 30;137(2):153-160

2. Sabba C, Pasculli G, Lenato GM, at al: Hereditary hemorrhagic telangiectasia: clinical features in ENG and ALK1 mutation carriers. J Thromb Haemost 2007 Jun;5(6):1149-1157

3. Abdalla SA, Letarte M: Hereditary haemorrhagic telangiectasia: current views on genetics and mechanisms of disease.J Med Genet 2006 Feb;43(2):97-110

4. Guttmacher AE, Marchuk DA, White RI Jr: Hereditary hemorrhagic telangiectasia. N Engl J Med 1995 Oct 5;333(14):918-924

5. Bayrak-Toydemir P, Mao R, Lewin S, et al: Hereditary hemorrhagic telangiectasia: an overview of diagnosis and management in the molecular era for clinicians. Genet Med 2004;6:175–191

Genomic DNA is extracted from whole blood. The ENG and ACVRL1 genes are amplified by PCR. The PCR product is then purified and sequenced in both directions using fluorescent dye-terminator chemistry. Sequencing products are separated on an automated sequencer and trace files analyzed for variations in the exons and intron/exon boundaries using mutation detection software and visual inspection. (Unpublished Mayo method)

Multiplex ligation-dependent probe amplification (MLPA) is used to detect the presence of large genomic deletions and duplications of all 15 exons of ENG and all 10 exons of ACVRL1. MLPA requires the hybridization of 2 adjacent probes to each exon; these probes are then amplified by PCR. Deletions are seen as decreased signal relative to control probes arising from the deleted exon(s), while duplications result in increased signal. (Package insert: SALSA MLPA Kit P093-B1 HHT/PPH1, MRC Holland)

Varies

81479 -Unlisted molecular pathology procedure