About Mutations in the MLH1 Gene

This information explains how having a mutation in the MLH1 gene may affect you and your family.

In this resource, the word “family” means family members related to you by blood. They are not related to you through marriage or adoption.

Your MLH1 gene normally helps prevent cancers. A mutation in this gene makes it stop working like it should. This increases your risk for certain types of cancers.

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What’s my risk for cancer if I have an MLH1 mutation?

If you have this gene mutation, this means you have a condition called Lynch syndrome. Lynch syndrome increases your risk for certain types of cancers, including:

  • Colorectal (colon and rectal) cancer 
  • Endometrial (uterine) cancer

Lynch syndrome may also increase your risk for other cancers, but this is less common. Examples of less common cancers linked to Lynch syndrome are:

  • Ovarian cancer
  • Stomach cancer
  • Small intestine (small bowel) cancer
  • Urinary tract cancer
  • Pancreatic cancer
  • Hepatobiliary tract cancer, which is cancer in the cells of the liver, bile ducts, and gallbladder
  • Brain cancer
  • Sebaceous carcinoma (cancer in the glands in your skin that make oil)

For more information, read Lynch Syndrome.

For more information, read Lynch Syndrome - www.mskcc.org/genetics/lynch-syndrome

As we learn more about this mutation, we may learn that it increases the risk for other types of cancers. Your genetic counselor will give you more information about your cancer risk if you have this mutation.

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What can I do about my cancer risk if I have an MLH1 mutation?

If you have a mutation, your genetic counselor will review your personal and family history of cancer and give you cancer screening recommendations.

They may recommend you start having cancer screenings at a younger age, have them more often than most people, or get specialized screenings to help find cancer as early as possible.

Some examples of these cancer screenings include:

  • Getting colonoscopies starting at an earlier age and more often than most people.
  • Getting an upper endoscopy (a procedure that lets your doctor see inside your stomach and small intestine).
  • Having a urinalysis (a test to look for blood in your urine).

Your genetic counselor may also talk with you about having surgery to try to keep cancer from developing, such as:

  • Surgery to remove your uterus to prevent endometrial cancer.
  • Surgery to remove your ovaries to prevent ovarian cancer.
  • Removing extra colon tissue during surgery for colon cancer to prevent getting colon cancer again.

If you decide to have surgery, talk with your genetic counselor about the right time to have it. Surgery to remove your uterus or ovaries affects your fertility (ability to have biological children). If you plan to have biological children, your genetic counselor can talk with you about your options.

Your genetic counselor will also talk with you about whether there are any other screening or prevention options that may be right for you.

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What happens if I don’t have an MLH1 mutation?

If you don’t have a mutation, your genetic counselor will review your personal and family history and talk with you about the general cancer screening guidelines you should follow.

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What does an MLH1 mutation mean for my family?

If you have this mutation, your biological parents, siblings, and children each have a 50% chance of having the same mutation. This means there’s an equal chance they will or won’t have the mutation. Your distant family members may also be at risk for having the same mutation.

Males and females have an equal chance of passing down this mutation in their family. You only need to inherit this mutation from one parent to have an increased risk for cancer.

Your genetic counselor will review your family history and talk with you about whether they recommend genetic testing for your blood relatives.

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What does this mean for family planning?

If you have an MLH1 mutation and plan to have children, there are options to prevent your children from inheriting the mutation. You may want to consider discussing these options especially if both you and your partner have an MLH1 mutation.

If you both have this mutation, there’s a chance your child could be born with a rare but serious condition called Constitutional Mismatch Repair Deficiency (CMMR-D) syndrome. CMMR-D syndrome causes a higher risk for childhood cancers. If you already have children, it’s unlikely they have CMMR-D since this is usually diagnosed early in life. For more information about genetic testing and family planning, talk with your genetic counselor.

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Contact Information

If you have any questions or concerns, talk with a genetic counselor in the Clinical Genetics Service. You can reach them Monday through Friday from 9:00 am to 5:00 pm  at 646-888-4050.
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