Hereditary Hemorrhagic Telangiectasia, ACVRL1 Gene, Known Mutation
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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 (nosebleed) 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 it 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 in 5,000 and 1 in 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.
ACVRL1 gene known mutation testing is for the genetic testing of individuals who are at risk for an ACVRL1 mutation that has been previously identified in the family. If the familial mutation is not known, the familial proband should be screened for ENG and ACVRL1 mutations via full gene analyses (HHTP / Hereditary Hemorrhagic Telangiectasia, ENG and ACVRL1 Full Gene Analysis). Once a mutation has been identified in a family, known mutation analysis can be performed in at-risk family members.
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)
Genetic testing of individuals at risk for a known activin A receptor, type II-like 1 (ACVRL1) familial mutation (associated with hereditary hemorrhagic telangiectasia)
An interpretive report will be provided.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Patients who have received a heterologous blood transfusion within the preceding 6 weeks, or who have received an allogeneic blood or marrow transplant, can have inaccurate genetic test results due to presence of donor DNA.
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.
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.
Other targeted mutation analyses available are:
-ENGK / Hereditary Hemorrhagic Telangiectasia, ENG Gene, Known Mutation
-HHTM / Hereditary Hemorrhagic Telangiectasia, ENG and ACVRL1 Large Deletion/Duplication, Molecular Analysis
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
An interpretive report will be provided.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Cohen J, Faughnan ME, Letarte M, et al: Cost comparison of genetic and clinical screening in families with hereditary hemorrhagic telangiectasia. Am J 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