Lynch syndrome, familial adenomatous polyposis, and Mut Y homolog 
(MYH)-associated polyposis are three major known types of inherited colorectal 
cancer, which accounts for up to 5% of all colon cancer cases. Lynch syndrome is 
most frequently caused by mutations in the mismatch repair genes MLH1, MSH2, 
MSH6, and PMS2 and is inherited in an autosomal dominant manner. Familial 
adenomatous polyposis is manifested as colonic polyposis caused by mutations in 
the APC gene and is also inherited in an autosomal dominant manner. Finally, 
MYH-associated polyposis is caused by mutations in the MUTYH gene and is 
inherited in an autosomal recessive manner but may or may not be associated with 
polyps. There are variants of both familial adenomatous polyposis (Gardner 
syndrome--with extracolonic features--and Turcot syndrome, which features 
medulloblastoma) and Lynch syndrome (Muir-Torre syndrome features sebaceous skin 
carcinomas, and Turcot syndrome features glioblastomas). Although a clinical 
diagnosis of familial adenomatous polyposis can be made using colonoscopy, 
genetic testing is needed to inform at-risk relatives. Because of the 
overlapping phenotypes between attenuated familial adenomatous polyposis, 
MYH-associated polyposis, and Lynch syndrome, genetic testing is needed to 
distinguish among these conditions. This distinction is important, especially 
for women with Lynch syndrome, who are at increased risk for gynecological 
cancers. Clinical testing for these genes has progressed rapidly in the past few 
years with advances in technologies and the lower cost of reagents, especially 
for sequencing. To assist clinical laboratories in developing and validating 
testing for this group of inherited colorectal cancers, the American College of 
Medical Genetics and Genomics has developed the following technical standards 
and guidelines. An algorithm for testing is also proposed.