MLH1/MSH2 Mutation Screen
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Lynch syndrome (also known as hereditary nonpolyposis colorectal cancer or HNPCC) is an autosomal dominant hereditary cancer syndrome associated with germline mutations in the mismatch repair genes, MLH1, MSH2, MSH6, and PMS2. Deletions within the 3-prime end of the EPCAM gene have also been associated with Lynch syndrome, as this leads to inactivation of the MSH2 promoter.
Lynch syndrome is predominantly characterized by significantly increased risks for colorectal and endometrial cancer. The lifetime risk for colorectal cancer is highly variable and dependent on the gene involved. The risk for colorectal cancer-associated MLH1 and MSH2 mutations (approximately 50%-80%) is generally higher than the risks associated with mutations in the other Lynch syndrome-related genes. The lifetime risk for endometrial cancer (approximately 25%-60%) is also highly variable. Other malignancies within the tumor spectrum include gastric cancer, ovarian cancer, hepatobiliary and urinary tract carcinomas, and small bowel cancer. The lifetime risks for these cancers are <15%. Of the 4 mismatch repair genes, mutations within the PMS2 gene confer the lowest risk for any of the tumors within the Lynch syndrome spectrum.
Several clinical variants of Lynch syndrome have been defined. These include Turcot syndrome, Muir-Torre syndrome, and homozygous mismatch repair mutations (also called constitutional mismatch repair deficiency syndrome). Turcot syndrome and Muir-Torre syndrome are associated with increased risks for cancers within the tumor spectrum described but also include brain/central nervous system malignancies and sebaceous carcinomas, respectively. Homozygous mismatch repair mutations, characterized by the presence of bi-allelic deleterious mutations within a mismatch repair gene, are associated with a different clinical phenotype defined by hematologic and brain cancers, cafe au lait macules, and childhood colon or small bowel cancer.
Four genes account for the majority of inherited (germline) mutations: approximately 40% will be associated with a mutation in hMSH2, 40% with a mutation in hMLH1, 10% with a mutation in hMSH6, 5% with a mutation in PMS2, and 5% other (unknown). Data from our laboratory suggests that large deletions, duplications, and other genomic rearrangements may account for approximately 10% and 30% of mutations in hMLH1 and hMSH2, respectively.
While the preferred method of testing for Lynch syndrome is to test a tumor from an affected individual for microsatellite instability (MSI) and immunohistochemistry (IHC) for the presence or absence of defective DNA mismatch repair, this is not always possible or desired. The MLH1/MSH2 Mutation Screen offers an alternative approach that consists of gene sequencing and multiplex ligation-dependent probe amplification (MLPA) for the 2 genes most commonly associated with Lynch syndrome.
See Hereditary Nonpolyposis Colorectal Cancer Testing Algorithm in Special Instructions for additional information.
Establishing a diagnosis of Lynch syndrome/hereditary nonpolyposis colorectal cancer (HNPCC)
Detection of mutations in MLH1 and MSH2, the 2 most common genes associated with Lynch syndrome, when microsatellite instability and immunohistochemistry tumor testing is not possible
Identification of a familial MLH1 or MSH2 mutation to allow for predictive testing in family members
All detected alterations will be evaluated according to American College of Medical Genetics and Genomics (ACMG) recommendations.(1) Variants will be classified based on known, predicted, or possible pathogenicity and reported with interpretive comments detailing their potential or known significance.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Some individuals who have a diagnosis of Lynch syndrome and/or involvement of MLH1 or hMSH2 may have a mutation that is not identified by this method (eg, promoter mutations, deep intronic mutations). The absence of a mutation, therefore, does not eliminate the possibility of a diagnosis of Lynch syndrome. For predictive testing of asymptomatic individuals, it is important to first document the presence of an MLH1 or MSH2 gene mutation in an affected family member.
In some cases, DNA alterations of undetermined significance may be identified.
Rare polymorphisms exist that could lead to false-negative or false-positive results. If results obtained do not match the clinical findings, additional testing should be considered.
A previous bone marrow transplant from an allogenic donor will interfere with testing. Call Mayo Medical Laboratories for instructions for testing patients who have received a bone marrow transplant.
Test results should be interpreted in the context of clinical findings, family history, and other laboratory data. Errors in our interpretation of results may occur if information given is inaccurate or incomplete.
We strongly recommend that patients undergoing predictive testing receive genetic counseling both prior to testing and after results are available.
In addition to disease-related probes, the multiplex ligation-dependent probe amplification technique utilizes probes localized to other chromosomal regions as internal controls. In certain circumstances, these control probes may detect other diseases or conditions for which this test was not specifically intended. Results of the control probes are not normally reported. However, in cases where clinically relevant information is identified, the ordering physician will be informed of the result and provided with recommendations for any appropriate follow-up testing.
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. Baudhuin LM, Burgart LJ, Leontovich O, Thibodeau SN: Use of microsatellite instability and immunohistochemistry testing for the identification of individuals at risk for Lynch Syndrome. Fam Cancer 2005;4:255-265
2. Umar A, Boland CR, Terdiman JP, et al: Revised Bethesda Guidelines for hereditary nonpolyposis colorectal cancer (Lynch syndrome) and microsatellite instability. J Natl Cancer Inst 2004 Feb;96(4):261-268
3. Lynch HT, de le Chapelle A: Hereditary colorectal cancer. N Engl J Med 2003 Mar;348(10):919-932
4. International Collaborative Group on Hereditary Non-Polyposis Colorectal Cancer. Mutation Database. Available from URL: http://www.insight-group.org