MSH3 Monoallelic gene

Associated Syndrome Name: Carrier Status for MSH3-associated Cancer Risk

MSH3 Monoallelic gene Overview

Carrier Status for MSH3-associated Cancer Risk 1, 2
  • Individuals with a mutation in only one copy of the MSH3 gene (a monoallelic mutation) are not believed to have any increased risk for cancer over people in the general population.
  • Individuals with mutations in both of their copies of the MSH3 gene (biallelic mutations) have a condition known as MSH3-associated cancer risk, which is believed to result in large numbers of colorectal polyps and an increased risk for colorectal cancer, as well as possible increased risks for other cancers. This patient does not have a diagnosis of MSH3-associated cancer risk, but may have relatives who are at risk for this condition. Please see the Information for Family Members section below for details.
  • Currently there are no medical management guidelines for patients with a single MSH3 mutation. However, this may change as we learn more, and therefore patients with monoallelic MSH3 mutations may benefit from consultation with healthcare providers who have expertise in medical genetics and the care of patients with hereditary cancer syndromes.

Information for Family Members

The following information for Family Members will appear as part of the MMT for a patient found to have a mutation in the MSH3 Monoallelic gene.

This patient's relatives are at risk for carrying the same mutation(s) and associated cancer risks as this patient. Cancer risks for females and males who have this/these mutation(s) are provided below.

Family members should talk to a healthcare provider about genetic testing. Close relatives such as parents, children, brothers and sisters have the highest chance of having the same mutation(s) as this patient. Other more distant relatives such as cousins, aunts, uncles, and grandparents also have a chance of carrying the same mutation(s). Testing of at-risk relatives can identify those family members with the same mutation(s) who may benefit from surveillance and early intervention.

This patient carries a single MSH3 mutation (monoallelic). This patient's relatives are at risk for carrying a single MSH3 mutation, or mutations in both copies of MSH3 (biallelic). Relatives who have inherited mutations in both copies of MSH3 have an increased risk for colorectal and possibly other cancers. Genetic testing may be appropriate for close family members to determine whether they are at an increased risk for colorectal and other cancers.


  1. Gupta S, et al. NCCN Clinical Practice Guidelines in Oncology® Genetic/Familial High-Risk Assessment: Colorectal. V 1.2021. May 11. Available at
  2. Adam R, et al. Exome Sequencing Identifies Biallelic MSH3 Germline Mutations as a Recessive Subtype of Colorectal Adenomatous Polyposis. Am J Hum Genet. 2016 99:337-51. PMID: 27476653.
Last Updated on 29-Sep-2022