Three or more family members with a confirmed diagnosis of colorectal cancer, one of whom is a first degree (parent, child, sibling) relative of the other two
Two successive affected generations
One or more colon cancers diagnosed under age 50 years
Familial adenomatous polyposis (FAP) has been excludedThe Amsterdam II criteria were developed in 1999 and improved the diagnostic sensitivity for Lynch syndrome by including cancers of the endometrium, small bowel, ureter and renal pelvis.Amsterdam Criteria II (all bullet points must be fulfilled):

Three or more family members with HNPCC-related cancers, one of whom is a first-degree relative of the other two
Two successive affected generations
One or more of the HNPCC-related cancers diagnosed under age 50 years
Familial adenomatous polyposis (FAP) has been excludedThe Bethesda criteria were developed in 1997 and later updated in 2004 by the National Cancer Institute to identify persons requiring further testing for Lynch syndrome through MSI. In contrast to the Amsterdam Criteria, the Revised Bethesda Guidelines use pathological data in addition to clinical information to help health care providers identify persons at high risk.Revised Bethesda Guidelines
If a person meets any 1 of 5 criteria the tumour(s) from the person should be tested for MSI:1. Colorectal cancer diagnosed before age 50
2. Presence of synchronous or metachronous colorectal or other Lynch syndrome associated cancers (e.g. cancers of endometrium, ovary, stomach, small bowel, pancreas, biliary tract, ureter, renal pelvis, brain, sebaceous glands, keratoacanthomas)
3. Colorectal cancer with MSI-high pathology in a person who is younger than 60 years of age
4.
This means the defective gene responsible for the disorder is located on an autosome (chromosome 8 is an autosome), and two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder. DNA repair
RECQL4 has a crucial role in DNA end resection that is the initial step required for homologous recombination (HR)-dependent double-strand break repair. When RECQL4 is depleted, HR-mediated repair and 5’ end resection are severely reduced in vivo. RECQL4 also appears to be necessary for other forms of DNA repair including non-homologous end joining, nucleotide excision repair and base excision repair. The association of deficient RECQL4-mediated DNA repair with accelerated aging is consistent with the DNA damage theory of aging. Diagnosis
Management
History
The condition was originally described by August von Rothmund (1830–1906) in 1868. Matthew Sydney Thomson (1894–1969) published further descriptions in 1936. See also
Poikiloderma vasculare atrophicans
List of cutaneous conditions
List of radiographic findings associated with cutaneous conditions

References
External links
GeneReviews/NCBI/NIH/UW entry on Rothmund-Thomson Syndrome
Poikiloderma of Rothmund-Thomson at NIHs Office of Rare Diseases