Sorted By Test Name - Mayo Medical Laboratories

HHTP
89394
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
(ACVK/89394 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)
Useful For: Genetic testing of individuals at risk for a known activin A receptor, type II-like 1
(ACVRL1) familial mutation (associated with hereditary hemorrhagic telangiectasia)
Interpretation: An interpretive report will be provided.
Reference Values:
An interpretive report will be provided.
Clinical References: 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
Hereditary Hemorrhagic Telangiectasia, ENG and ACVRL1 Full
Gene Analysis
Clinical Information: 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 oneâ€s lifetime. For example,
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