Originally published February 29, 2016
Lynch syndrome is an autosomal dominant condition. This means that a person who carries one copy of a mutation in any of the genes known to cause Lynch syndrome is at increased risk to develop multiple adult-onset cancers, especially those of the colon, uterus, and ovaries.
A person who carries two mutations in the same gene in any of the genes associated with Lynch syndrome (MLH1, MSH2, MSH6, PMS2) has a completely different syndrome called Constitutional Mismatch Repair Deficiency (CMMRD). This usually occurs when a person inherits one mutation from their father and the other from their mother. This rare condition is associated with a high risk of early-onset cancers, including childhood onset cancers of the brain and blood. Café au lait spots, flat light-brown birthmarks on the skin, are also common.
https://www.mygenecounsel.com/getting-the-cmmrd-facts-straight/
Lynch Syndrome Ireland 