Lynch syndrome: a pediatric perspective.

Colorectal cancer is a rare disease in the pediatric age group and, when present, suggests an underlying genetic predisposition. The most common hereditary colon cancer susceptibility condition, Lynch syndrome (LS), previously known as hereditary nonpolyposis colorectal cancer, is an autosomal dominant condition caused by a germline mutation in 1 of 4 DNA mismatch repair (MMR) genes: MLH1, MSH2, MSH6, or PMS2. The mutation-prone phenotype of this disorder is associated with gastrointestinal, endometrial, and other cancers and is now being identified in both symptomatic adolescents with malignancy as well in asymptomatic mutation carriers who are at risk for a spectrum of gastrointestinal and other cancers later in life. We review the DNA MMR system, our present understanding of LS in the pediatric population, and discuss the newly identified biallelic form of the disease known as constitutional mismatch repair deficiency syndrome. Both family history and tumor characteristics can help to identify patients who should undergo genetic testing for these cancer predisposition syndromes. Patients who carry either single allele (LS) or double allele (constitutional mismatch repair deficiency syndrome) mutations in the MMR genes benefit from cancer surveillance programs that target both the digestive and extraintestinal cancer risk of these diseases. Because spontaneous mutation in any one of the MMR genes is extremely rare, genetic counseling and testing are suggested for all at-risk family members.

Oncologic surveillance for subjects with biallelic mismatch repair gene mutations: 10 year follow-up of a kindred.

BACKGROUND: Heterozygous germline mutations in DNA mismatch repair (MMR) genes cause Lynch syndrome. Biallelic MMR mutations cause a distinct syndrome characterized by brain tumors, lymphoid malignancies, and gastrointestinal cancers during childhood. These children usually succumb to multiple cancers before adulthood. We developed a surveillance protocol aiming at early detection for these individuals and report the 10-year experience with a kindred. METHODS: On the basis of genetic testing and early age tumors, the kindred started a cancer surveillance protocol based on the crude estimates of cancer risks and available cancer screening: imaging, endoscopy, and hematologic tests. RESULTS: Over the 10-year follow-up period, the screening protocol detected 15 tumors. These included three high-grade adenomatous colonic polyps and two colon cancers. In one child, MRI revealed an asymptomatic anaplastic astrocytoma which was treated by complete resection and radiation. All three cancers identified during surveillance were small and asymptomatic at diagnosis. The two sisters are currently 16 and 18 years of age with no evidence of malignant disease. Both parents have annual colonoscopies and the father at 43 years had two colonic adenomatous polyps. CONCLUSIONS: We report on the long-term outcome in patients with biallelic MMR mutations who benefited from prophylactic cancer surveillance. Genetic screening and subsequent surveillance led to earlier recognition of asymptomatic tumors at stages more amenable to resection and probable cure. Multicenter collaboration and implementation of surveillance guidelines is necessary to further determine genotype-phenotype correlations.

The gastrointestinal phenotype of germline biallelic mismatch repair gene mutations.

OBJECTIVES: A novel cancer syndrome associated with biallelic mismatch repair (MMR) mutations has been described recently. Patients presenting with childhood-onset gastrointestinal (GI) cancers may carry biallelic MMR mutations and have a distinct phenotype from classic Lynch syndrome. The aim of this study was to characterize patients with GI small bowel and/or colorectal cancers (CRCs) who have germline biallelic MMR mutations. METHODS: A search of a Canadian GI cancer registry and literature review to identify patients with biallelic MMR was conducted. RESULTS: The database identified 237 patients with intestinal cancer diagnosed before the age of 35 years. Five (2.1%) patients had biallelic MMR mutations. Overall, 32 individuals, from 29 families, with biallelic MMR gene mutations and GI cancers were identified by the registry and literature review. Among the 29 patients with CRCs, the mean age of first cancer diagnosis was 16.4 years (range: 5-28). More than one-third of patients had multiple colorectal adenomas (>10 polyps). Six individuals with biallelic MMR gene mutations have been reported with small bowel adenocarcinoma (mean age 20 years (range: 11-41)). Café-au-lait (CAL) macules were reported in 72% and, based on mutation analysis, consanguinity was suspected in 52% of kindred. Of the 29 kindred, 19 (66%) had PMS2 mutations, 6 (21%) had MSH6 mutations, 3 (10%) had MLH1 mutations, and 1 (3%) had MSH2 mutation. CONCLUSIONS: Biallelic MMR mutations are an underrecognized cause of small bowel and colonic cancers in children and young adults. This distinct phenotype includes multiple adenomatous polyps and CAL skin lesions. It is important to identify such patients, so that families can be referred for genetic testing and counseling.

Phenotypic and genotypic characterisation of biallelic mismatch repair deficiency (BMMR-D) syndrome.

Lynch syndrome, the most common inherited colorectal cancer syndrome in adults, is an autosomal dominant condition caused by heterozygous germ-line mutations in DNA mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2. Inheriting biallelic (homozygous) mutations in any of the MMR genes results in a different clinical syndrome termed biallelic mismatch repair deficiency (BMMR-D) that is characterised by gastrointestinal tumours, skin lesions, brain tumours and haematologic malignancies. This recently described and under-recognised syndrome can present with adenomatous polyps leading to early-onset small bowel and colorectal adenocarcinoma. An important clue in the family history that suggests underling BMMR-D is consanguinity. Interestingly, pedigrees of BMMR-D patients typically show a paucity of Lynch syndrome cancers and most parents are unaffected. Therefore, a family history of cancers is often non-contributory. Detection of BMMR-D can lead to more appropriate genetic counselling and the implementation of targeted surveillance protocols to achieve earlier tumour detection that will allow surgical resection. This review describes an approach for diagnosis and management of these patients and their families.

Childhood cancers in families with and without Lynch syndrome.

Inheritance of a germline mutation in one of the DNA mismatch repair (MMR) genes or the EPCAM gene is associated with an increased risk of colorectal cancer, endometrial cancer, and other adult malignancies (Lynch syndrome). The risk of childhood cancers in Lynch syndrome families, however, is not well studied. Using data from the Colon Cancer Family Registry, we compared the proportion of childhood cancers (diagnosed before 18 years of age) in the first-, second-, and third-degree relatives of 781 probands with a pathogenic mutation in one of the MMR genes; MLH1 (n = 275), MSH2 (n = 342), MSH6 (n = 99), or PMS2 (n = 55) or in EPCAM (n = 10) (Lynch syndrome families), with that of 5073 probands with MMR-deficient colorectal cancer (non-Lynch syndrome families). There was no evidence of a difference in the proportion of relatives with a childhood cancer between Lynch syndrome families (41/17,230; 0.24%) and non-Lynch syndrome families (179/94,302; 0.19%; p = 0.19). Incidence rate of all childhood cancers was estimated to be 147 (95% CI 107-206) per million population per year in Lynch syndrome families and 115 (95% CI 99.1-134) per million population per year in non-Lynch syndrome families. There was no evidence for a significant increase in the risk of all childhood cancers, hematologic cancers, brain and central nervous system cancers, Lynch syndrome-associated cancers, or other cancers in Lynch syndrome families compared with non-Lynch syndrome families. Larger studies, however, are required to more accurately define the risk of specific individual childhood cancers in Lynch syndrome families.

Genetic predisposition to colorectal cancer: new pieces in the pediatric puzzle.

Colorectal cancer is rare in childhood. The 2 best characterized familial syndromes, hereditary nonpolyposis colorectal cancer (HNPCC, Lynch syndrome) and familial adenomatous polyposis (FAP), are autosomal dominant inherited disorders. HNPCC is relevant to pediatric gastroenterology practice because children and adolescents with underlying colorectal cancer can have germ-line mutations of mismatch repair genes. Recent attention has focused on characterizing genetic predisposition to attenuated FAP in individuals who do not have germ-line mutations in the APC gene. The identification of a second mechanistic explanation called MYH-associated polyposis (MAP), which is an autosomal-recessive condition, has important implications for both screening and management strategies. Hereditary colorectal cancer including HNPCC, FAP, attenuated FAP and MYH-associated polyposis in children are the subject of this review.