Key Points

  • MAP is a rare recessively inherited condition associated with abnormalities in the MYH gene.  A recessive condition means that both inherited copies of the MYH gene (one copy is inherited from each parent) has an abnormality or mutation.  The mutation in both MYH genes means that the MYH gene cannot do its job properly
  • MAP is characterised by the finding of multiple bowel polyps or outgrowths (adenomas) on the lining of the large bowel
  • Bowel cancer develops from adenomatous bowel polyps over a period of time
  • Adenomas in the general population do not usually occur until the age 40–50 years and then only in small numbers
  • People with MAP generally develop greater than 20 adenomatous bowel polyps at a younger age and the majority of people with MAP will develop bowel cancer by age 60 years
  • Surgery to remove the majority of the large bowel prevents individuals with MAP from developing bowel cancer.  This surgery is normally recommended before age 60 years
  • Yearly bowel screening after surgery is required for the part of the large bowel that remains to help prevent cancers developing
  • Siblings (brothers and sisters) of people with MAP have a 1 in 4 risk of inheriting two abnormal copies of the MYH gene.  If you have two abnormal copies of the MYH gene, you will have MAP.  Genetic testing is recommended for siblings of people with MAP
  • Children of people with MAP will inevitably each carry one abnormal copy of the MYH gene.  However, carrying one abnormal copy of the MYH gene does not clearly increase a person’s risk of developing bowel cancer.  Therefore, genetic testing and bowel screening by colonoscopy are not routinely recommended or available for children of people with MAP

The aim of the NZFGCS is to reduce the number of cancers occurring in families by facilitating the required bowel screening for registered families

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