A novel MSH2 germline mutation in homozygous state in two brothers with colorectal cancers diagnosed at the age of 11 and 12 years

Rare single-nucleotide variants of MLH1 and MSH2 genes in patients with Lynch syndrome

BACKGROUND

Approximately 5% of colorectal cancers (CRCs) are hereditary. Lynch syndrome (LS), also known as hereditary nonpolyposis colorectal cancer (HNPCC), is the most common form of recognized hereditary CRC. Although Iran, as a developing country, has a high incidence of CRC, the spectrum of variants has yet to be thoroughly investigated.

AIMS

This study aimed to investigate pathogenic and non-pathogenic variants in MLH1 and MSH2 genes in Iranian patients with suspected Lynch syndrome (sLS).

METHODS AND RESULTS

In the present study, 25 peripheral blood samples were collected from patients with sLS and high microsatellite instability (MSI-H). After DNA extraction, all samples underwent polymerase chain reaction and Sanger sequencing to identify the variants in the exons of MLH1 and MSH2 genes. The identified variants were interpreted using prediction tools, and were finally reported under ACMG guidelines. In our study population, 13 variants were found in the MLH1 gene and 8 in the MSH2 gene. Interestingly, 7 of the 13 MLH1 variants and 3 of the 8 MSH2 variants were novel, whereas the remaining variants were previously reported or available in databases. In addition, some patients with sLS did not have variants in the exons of the MLH1 and MSH2 genes. The variants detected in the MLH1 and MSH2 genes had specific characteristics regarding the number, area of occurrence, and their relationship with demographic and clinicopathologic features.

CONCLUSION

Overall, our results suggest that analysis of MLH1 and MSH2 genes alone is insufficient in the Iranian population, and more comprehensive tests are recommended for detecting LS.

A novel deleterious c.2656G>T MSH2 germline mutation in a Pakistani family with a phenotypic overlap of hereditary breast and ovarian cancer and Lynch syndrome

Background

Hereditary breast and ovarian cancer syndrome (HBOC) and Lynch syndrome (LS) account for a significant proportion of inherited gynecologic malignancies, mainly caused by pathogenic germline mutations in the BRCA1 and BRCA2 genes or in mismatch repair (MMR) genes, such as MLH1 and MSH2. Women harboring deleterious mutations in these genes have increased life-time risks of developing a number of malignancies including ovarian cancer. Since there is a phenotypic overlap of HBOC and LS, timely identification of individuals at-risk of a particular syndrome is crucial in order to optimize cancer risk management.

Case presentation

We report a novel pathogenic MSH2 mutation, c.2656G > T, which was identified in a 67-year-old female patient with breast cancer, who had previously tested negative for a deleterious mutation in the breast cancer susceptibility genes BRCA1, BRCA2, CHEK2 or RAD51C. The patient reported a personal history of endometrial cancer diagnosed at age 48, and a strong family history of breast and ovarian cancer, as well as several other malignancies within the spectrum of LS. The novel mutation was also found in the index patient’s daughter and a niece, who were diagnosed with endometrial and ovarian cancer, respectively. Breast and endometrial tumors from c.2656G > T mutation carriers showed loss of MSH2 and MSH6 protein expression. The mutation was absent in the control population.

Conclusions

Our finding suggests that testing for MMR genes may be of benefit to BRCA1/2 negative families with overlapping HBOC and LS phenotype in Pakistan. It is clinically significant to identify individuals harboring mutations in genes linked with a particular syndrome so that they can benefit from targeted life-saving cancer surveillance and preventive strategies.

Gastrointestinal Findings in the Largest Series of Patients With Hereditary Biallelic Mismatch Repair Deficiency Syndrome: Report from the International Consortium

OBJECTIVES

Hereditary biallelic mismatch repair deficiency (BMMRD) is caused by biallelic mutations in the mismatch repair (MMR) genes and manifests features of neurofibromatosis type 1, gastrointestinal (GI) polyposis, and GI, brain, and hematological cancers. This is the first study to characterize the GI phenotype in BMMRD using both retrospective and prospective surveillance data.

METHODS

The International BMMRD Consortium was created to collect information on BMMRD families referred from around the world. All patients had germline biallelic MMR mutations or lack of MMR protein staining in normal and tumor tissue. GI screening data were obtained through medical records with annual updates.

RESULTS

Thirty-five individuals from seven countries were identified with BMMRD. GI data were available on 24 of 33 individuals (73%) of screening age, totaling 53 person-years. The youngest age of colonic adenomas was 7, and small bowel adenoma was 11. Eight patients had 19 colorectal adenocarcinomas (CRC; median age 16.7 years, range 8-25), and 11 of 18 (61%) CRC were distal to the splenic flexure. Eleven patients had 15 colorectal surgeries (median 14 years, range 9-25). Four patients had five small bowel adenocarcinomas (SBC; median 18 years, range 11-33). Two CRC and two SBC were detected during surveillance within 6-11 months and 9-16 months, respectively, of last consecutive endoscopy. No patient undergoing surveillance died of a GI malignancy. Familial clustering of GI cancer was observed.

CONCLUSIONS

The prevalence and penetrance of GI neoplasia in children with BMMRD is high, with rapid development of carcinoma. Colorectal and small bowel surveillance should commence at ages 3-5 and 8 years, respectively.

Early onset of colorectal cancer in a 13-year-old girl with Lynch syndrome

Lynch syndrome is the most common inherited colon cancer syndrome. Patients with Lynch syndrome develop a range of cancers including colorectal cancer (CRC) and carry a mutation on one of the mismatched repair (MMR) genes. Although CRC usually occurs after the fourth decade in patients with Lynch syndrome harboring a heterozygous MMR gene mutation, it can occur in children with Lynch syndrome who have a compound heterozygous or homozygous MMR gene mutation. We report a case of CRC in a 13-year-old patient with Lynch syndrome and congenital heart disease. This patient had a heterozygous mutation in MLH1 (an MMR gene), but no compound MMR gene defects, and a K-RAS somatic mutation in the cancer cells.

Paediatric intestinal cancer and polyposis due to bi-allelic PMS2 mutations: case series, review and follow-up guidelines

BACKGROUND

Bi-allelic germline mutations of one of the DNA mismatch repair genes, so far predominantly found in PMS2, cause constitutional MMR-deficiency syndrome. This rare disorder is characterised by paediatric intestinal cancer and other malignancies. We report the clinical, immunohistochemical and genetic characterisation of four families with bi-allelic germline PMS2 mutations. We present an overview of the published gastrointestinal manifestations of CMMR-D syndrome and propose recommendations for gastro-intestinal screening.

METHODS AND RESULTS

The first proband developed a cerebral angiosarcoma at age 2 and two colorectal adenomas at age 7. Genetic testing identified a complete PMS2 gene deletion and a frameshift c.736_741delinsTGTGTGTGAAG (p.Pro246CysfsX3) mutation. In the second family, both the proband and her brother had multiple intestinal adenomas, initially wrongly diagnosed as familial adenomatous polyposis. A splice site c.2174+1G>A, and a missense c.137G>T (p.Ser46Ile) mutation in PMS2 were identified. The third patient was diagnosed with multiple colorectal adenomas at age 11; he developed a high-grade dysplastic colorectal adenocarcinoma at age 21. Two intragenic PMS2 deletions were found. The fourth proband developed a cerebral anaplastic ganglioma at age 9 and a high-grade colerectal dysplastic adenoma at age 10 and carries a homozygous c.2174+1G>A mutation. Tumours of all patients showed microsatellite instability and/or loss of PMS2 expression.

CONCLUSIONS

Our findings show the association between bi-allelic germline PMS2 mutations and severe childhood-onset gastrointestinal manifestations, and support the notion that patients with early-onset gastrointestinal adenomas and cancer should be investigated for CMMR-D syndrome. We recommend yearly follow-up with colonoscopy from age 6 and simultaneous video-capsule small bowel enteroscopy from age 8.

[Differential diagnostics of hereditary colorectal cancer syndromes. The role of pathology]

One third of colorectal carcinomas (CRC) show familial clustering of which about 5% have a monogenetic trait. Distinction between disease with and without polyposis, tumor histology and tumor spectrum in a given patient are all of diagnostic relevance. Familial adenomatous polyposis (FAP) underlies approximately 1% of CRC characterized by rapidly forming (>100) adenomas. In contrast to these about 2%-3% of CRC have a hereditary background without polyposis (HNPCC). This is the only hereditary tumour syndrome to date for which a tissue-based molecular screening test is available. Accordingly, expression analysis of mismatch repair genes (MSH2, MSH6 and MLH1, PMS2) is performed first. In the case of an equivocal result with no complete loss of expression testing of microsatellite instability (MSI) is added. In contrast to the other diseases MYH-associated polyposis (MAP) follows a recessive trait with polyp numbers usually between 15-30 adenomas and should be distinguished from attenuated forms of FAP with <100 polyps in the differential diagnosis. In the case of suspected familial cancer syndrome genetic counseling is warranted in order to decide ultimately whether there is an indication for genetic testing (evidence of a germ-line mutation).

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.

Impact of 226C>T MSH2 gene mutation on cancer phenotypes in two HNPCC-associated highly-consanguineous families from Kuwait: emphasis on premarital genetic testing

Lynch syndrome or hereditary nonpolyposis colorectal cancer (HNPCC) is one of the commonest cancer susceptibility syndromes. It is characterized by early onset colon cancer and a variety of extracolonic tumours. Germline mutations in the DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS1, and PMS2) are responsible for this disorder. Identifying an affected individual depends on the tumour histopathology, family history that fulfils the Amsterdam and/or Bethesda criteria, tumour immunohistochemistry, microsatellite instability, and finally molecular analysis of an affected member. It is a laborious, time consuming and expensive procedure, which needs the effort of a multi-disciplinary team. However, once the diagnosis is established and germline defect is identified, other high risk pre-symptomatic carriers could be offered intensive surveillance and management as a preventive measure against cancer development. Here, we present two large highly consanguineous HNPCC-families from Kuwait in whom a founder MSH2 mutation was identified. The relationship between this mutation and cancer expressivity in two large consanguineous families harbouring other genetic defects is discussed. Moreover, we shed light on the challenges pertaining to diagnosis, screening, premarital counselling of couples and prenatal diagnosis of offspring with biallelic MSH2 gene mutation.

Report of a family segregating mutations in both the APC and MSH2 genes: juvenile onset of colorectal cancer in a double heterozygote

BACKGROUND AND AIMS

Mutations in DNA mismatch repair genes are associated with high risk of digestive malignancies [hereditary non-polyposis colorectal cancer (HNPCC); Lynch syndrome]; mutations of APC and MYH are associated with classic and attenuated familial adenomatous polyposis (FAP). Although the early onset of tumors in both syndromes is characteristic of their genetic origin, pediatric malignancies remain rare. Certain reports have found familial colorectal cancer (CRC) occurring in very young patients associated with mutations in more than one gene.

MATERIALS AND METHOD

A family corresponding to the Amsterdam criteria for HNPCC, including two cases of colorectal cancer before the age of 25 years, was analyzed for mutations in the MSH2 genes by sequencing. Because polyposis was observed in a patient who developed CRC at age 16, the APC gene was also sequenced.

RESULTS

A truncating mutation in the MSH2 gene, c.258_259delTG, was carried by patients developing cancer of the colon (two patients), uterus, kidney, bladder, and/or small intestine at ages 16, 24, 43, 44, 45, and 57, respectively. A patient with CRC at age 16 was found to carry the APC c.3183_3187del5 mutation as well as the MSH2 mutation, and it is inferred that her father, deceased of CRC at age 24, was also a double heterozygote.

INTERPRETATION

These results confirm that vigilance is required when interpreting molecular results for families with very young patients, as more than one gene may contribute to the genetic risk. Cancer screening measures must also be adapted to the earlier and more penetrant risk to double heterozygotes.

Constitutional mismatch repair-deficiency syndrome: have we so far seen only the tip of an iceberg?

Heterozygous mutations in one of the mismatch repair (MMR) genes MLH1, MSH2, MSH6 and PMS2 cause the dominant adult cancer syndrome termed Lynch syndrome or hereditary non-polyposis colorectal cancer. During the past 10 years, some 35 reports have delineated the phenotype of patients with biallelic inheritance of mutations in one of these MMR genes. The patients suffer from a condition that is characterised by the development of childhood cancers, mainly haematological malignancies and/or brain tumours, as well as early-onset colorectal cancers. Almost all patients also show signs reminiscent of neurofibromatosis type 1, mainly café au lait spots. Alluding to the underlying mechanism, this condition may be termed as "constitutional mismatch repair-deficiency (CMMR-D) syndrome". To give an overview of the current knowledge and its implications of this recessively inherited cancer syndrome we summarise here the genetic, clinical and pathological findings of the so far 78 reported patients of 46 families suffering from this syndrome.

Genetic testing of children at risk for adult onset conditions: when is testing indicated?

We report a family with an extensive history of colon cancer consistent with hereditary nonpolyposis colorectal cancer (HNPCC). A specific disease causing mutation was identified in affected individuals; p.W714X MLH1 mutation. Given the very young age of onset of cancer in some affected family members, with the youngest affected individual being 19 years of age, genetic counseling was recommended to children as young as 9 years. Ethical issues arose when affected families requested genetic testing for their underage children. Here we describe and debate the value of offering molecular testing for this adult onset disorder to several children in this particular family. We also examine possible molecular causes for the very young age of onset in some family members.

Higher occurrence of childhood cancer in families with germline mutations in BRCA2, MMR and CDKN2A genes

The contribution of hereditary factors for development of childhood tumors is limited to some few known syndromes associated with predominance of tumors in childhood. Occurrence of childhood tumors in hereditary cancer syndromes such as BRCA1/2 associated breast and ovarian cancer, DNA-mismatch repair (MMR) genes associated hereditary non polyposis colorectal cancer and CDKN2A associated familial malignant melanoma are very little studied. Herein we report the prevalence of childhood tumors (diagnosed<or=18 years of age) in families identified with mutation in the BRCA1/2, MMR and CDKN2A genes. Using pedigrees at the Regional Oncogenetic Clinic at Lund University Hospital, the prevalence of childhood cancer was estimated in families with mutations in the BRCA1 (n=98), BRCA2 (n=43) MMR (MLH1, MSH2 MSH6) (n=31) and CDKN2A (n=15) genes in comparison with population based control families (n=854). Compared with the control group, a significantly higher prevalence of childhood cancer was found in families with mutations in BRCA2 (9.3% vs. 0.8% P=0.001), MMR genes (19.4% vs. 0.8% P<0.001) and CDKN2A (20.0% vs. 0.8% P<0.001), but not in families with BRCA1 mutations (1.0% vs. 0.8% P=0.6). Further analyses showed an increased risk for childhood tumors in families with mutations in BRCA2 (OR 12.4; 95% CI 3.5-44.1), MMR genes (OR 29.0; 95% CI 9.1-92.6), and CDKN2A (OR 30.2; 95% CI 7.0-131.1). This study suggests that the risk for childhood tumors is increased in families with germline mutations in the BRCA2, MMR and CDKN2A genes.

Familial T-cell non-Hodgkin lymphoma caused by biallelic MSH2 mutations

Familial non-Hodgkin lymphoma (NHL) is rare and in most cases, no underlying cause is identifiable. We report homozygous truncating mutations in the mismatch repair gene MSH2 (226C-->T; Q76X) in three siblings who each developed T-cell NHL in early childhood. All three children had hyperpigmented and hypopigmented skin lesions. Constitutional biallelic MSH2 mutations have previously been reported in five individuals, all of whom developed malignancy in childhood. Familial lymphoma has not been reported in this context or in association with biallelic mutations in the other mismatch repair genes MLH1, MSH6 or PMS2. In addition, hypopigmented skin lesions have not previously been reported in biallelic MSH2 carriers. Our findings therefore expand the spectrum of phenotypes associated with biallelic MSH2 mutations and identify a new cause of familial lymphoma. Moreover, the diagnosis has important management implications as it allows the avoidance of chemotherapeutic agents likely to be ineffective and mutagenic in the proband, and the provision of cascade genetic testing and tumour screening for relatives.

Biallelic PMS2 mutations and a distinctive childhood cancer syndrome

Biallelic mutations in PMS2, a gene usually associated in heterozygous form with hereditary nonpolyposis colorectal cancer (HNPCC), results in a recently described childhood cancer syndrome. The tumor spectrum encompasses atypical brain cancers, hematologic malignancies, and colonic polyposis and cancer. Cutaneous stigmata resembling café-au-lait macules with more diffuse margins are frequently seen. Onset is as young as 2 years. The risk of second malignancy is high. Evidence exists for surveillance for bowel cancer, but surveillance for the wider tumor spectrum is of uncertain benefit. We report a consanguineous Australian-Lebanese family with multiple affected individuals shown to be homozygous for a PMS2 exon 7 deletion. We also review published cases of biallelic mutations in HNPCC-related genes. Early recognition of this familial cancer syndrome is critical, and should prompt investigation for familial HNPCC mutations.

Thyroid cancer in a patient with a germline MSH2 mutation. Case report and review of the Lynch syndrome expanding tumour spectrum

Lynch syndrome (HNPCC) is a dominantly inherited disorder characterized by germline defects in DNA mismatch repair (MMR) genes and the development of a variety of cancers, predominantly colorectal and endometrial. We present a 44-year-old woman who was shown to carry the truncating MSH2 gene mutation that had previously been identified in her family. Recently, she had been diagnosed with an undifferentiated carcinoma of the thyroid and an adenoma of her coecum. Although the thyroid carcinoma was not MSI-high (1 out of 5 microsatellites instable), it did show complete loss of immunohistochemical expression for the MSH2 protein, suggesting that this tumour was not coincidental. Although the risks for some tumour types, including breast cancer, soft tissue sarcoma and prostate cancer, are not significantly increased in Lynch syndrome, MMR deficiency in the presence of a corresponding germline defect has been demonstrated in incidental cases of a growing range of tumour types, which is reviewed in this paper. Interestingly, the MSH2-associated tumour spectrum appears to be wider than that of MLH1 and generally the risk for most extra-colonic cancers appears to be higher for MSH2 than for MLH1 mutation carriers. Together with a previously reported case, our findings show that anaplastic thyroid carcinoma can develop in the setting of Lynch syndrome. Uncommon Lynch syndrome-associated tumour types might be useful in the genetic analysis of a Lynch syndrome suspected family if samples from typical Lynch syndrome tumours are unavailable.

Novel biallelic mutations in MSH6 and PMS2 genes: gene conversion as a likely cause of PMS2 gene inactivation

Since the first report by our group in 1999, more than 20 unrelated biallelic mutations in DNA mismatch repair genes (MMR) have been identified. In the present report, we describe two novel cases: one carrying compound heterozygous mutations in the MSH6 gene; and the other, compound heterozygous mutations in the PMS2 gene. Interestingly, the inactivation of one PMS2 allele was likely caused by gene conversion. Although gene conversion has been suggested to be a mutation mechanism underlying PMS2 inactivation, this is the first report of its involvement in a pathogenic mutation. The clinical features of biallelic mutation carriers were similar to other previously described patients, with the presence of café-au-lait spots (CALS), early onset of brain tumors, and colorectal neoplasia. Our data provide further evidence of the existence, although rare, of a distinct recessively inherited syndrome on the basis of MMR constitutional inactivation. The identification of this syndrome should be useful for genetic counseling, especially in families with atypical hereditary nonpolyposis colon cancer (HNPCC) associated with childhood cancers, and for the clinical surveillance of these mutation carriers.

Homozygous PMS2 germline mutations in two families with early-onset haematological malignancy, brain tumours, HNPCC-associated tumours, and signs of neurofibromatosis type 1

Heterozygous germline mutations in mismatch repair (MMR) genes MLH1, PMS2, MSH2, and MSH6 cause Lynch syndrome. New studies have indicated that biallelic mutations lead to a distinctive syndrome, childhood cancer syndrome (CCS), with haematological malignancies and tumours of brain and bowel early in childhood, often associated with signs of neurofibromatosis type 1. We provide further evidence for CCS reporting on six children from two consanguineous families carrying homozygous PMS2 germline mutations. In family 1, all four children had the homozygous p.I590Xfs mutation. Two had a glioblastoma at the age of 6 years and one of them had three additional Lynch-syndrome associated tumours at 15. Another sibling suffered from a glioblastoma at age 9, and the fourth sibling had infantile myofibromatosis at 1. In family 2, two of four siblings were homozygous for the p.G271V mutation. One had two colorectal cancers diagnosed at ages 13 and 14, the other had a Non-Hodgkin's lymphoma and a colorectal cancer at ages 10 and 11, respectively. All children with malignancies had multiple café-au-lait spots. After reviewing published cases of biallelic MMR gene mutations, we provide a concise description of CCS, revealing similarities in age distribution with carriers of heterozygous MMR gene mutations.

Constitutive deficiency in DNA mismatch repair

Mutations in the DNA mismatch repair (MMR) genes are associated with the inheritance of hereditary non-polyposis colorectal cancer, also known as Lynch syndrome, a cancer syndrome with an average age at onset of 44. Individuals presenting with colorectal cancer are diagnosed with Lynch I, whereas individuals who present with extra-colonic tumors (such as endometrial, stomach, etc.) are identified as patients with Lynch syndrome II. Recently, 30 families have been reported with inheritance of biallelic mutations in the MMR genes. Here we summarize the phenotype of individuals with inheritance of homozygous or compound heterozygous mutations in the MMR genes that result in a complete lack of protein or greatly compromised protein function. In contrast to individuals with Lynch syndrome I and II, individuals with no MMR function present with childhood onset of hematological and brain malignancies, whereas residual MMR function can also result in gastrointestinal cancers and an age of onset in the second to fourth decade. Individuals with biallelic MMR mutations often present with café-au-lait spots, regardless of the level of MMR function remaining. Thus, the inheritance of two MMR gene mutations is a separate entity from Lynch I or II or the subtypes Turcot and Muir-Torre.

Biallelic germline mutations of mismatch-repair genes: a possible cause for multiple pediatric malignancies

BACKGROUND

Heterozygous defects in mismatch-repair (MMR) genes cause hereditary nonpolyposis colorectal cancer (HNPCC). In this syndrome, tumors typically arise from age 25 years onward. Case reports have shown that homozygosity or compound heterozygosity for MMR gene mutations can cause multiple tumors in childhood, sometimes combined with neurofibromatosis type I (NF1)-like features. Therefore, the authors studied the role of homozygosity or compound heterozygosity (CZ) for MMR gene defects in children with multiple primary tumors.

METHODS

A database that contained all pediatric oncology patients who were seen between 1982 and 2003 at the author's institution was queried to identify patients aged <16 years with more than 1 tumor for whom tissue of at least 1 tumor was available. On isolated DNA, microsatellite instability (MSI) and immunohistochemistry of MMR proteins were assessed.

RESULTS

In total, 15 patients with more than 1 tumor were identified. Abnormal test results were obtained in 2 of them, including 1 patient who was diagnosed at age 4 years with a glioblastoma (MSI-stable; no human mutL homolog 1 [MLH1] or postmeiotic segregation increased, Saccharomyces cerevisiae 2 [PMS2] expression) and a Wilms tumor (high MSI; no MLH1 or PMS2 expression). Apart from >6 cafe-au-lait spots, he had no other signs of NF1. The patient had CZ identified for a pathogenic MLH1 mutation (593delAG frameshift) and an unclassified MLH1 variant (Met35Asn). There was strong evidence that this unclassified variant was a pathogenic mutation. The second patient was diagnosed with a non-Hodgkin lymphoma (no tissue available) and an anaplastic oligodendroglioma (low MSI; no MSH6 expression) at age 4 years and 6 years, respectively. His brother had died of a medulloblastoma at age 6 years (low MSI, no MSH6 expression). Both boys had cafe-au-lait spots. Further genetic testing was not possible.

CONCLUSIONS

Carriage of biallelic MMR gene defects can be associated with multiple malignancies in childhood that may differ from the standard spectrum of HNPCC tumor types. In 15 pediatric patients with multiple malignancies, the authors identified 1 clear case and 1 possible case of biallelic MMR gene defect. Recognition of the inherited nature of the tumors in these patients is important for counseling these patients and their families.

Pediatric adenomatous polyposis syndromes: an update

Juvenile polyps are a common finding in the pediatric population. In contrast, colon adenomas, which are viewed as dysplastic precancerous lesions, are found sporadically in late adulthood. Adenomas in children and young adults are highly unusual and suggest one of several forms of inherited colorectal cancer. These disorders show a predilection to early adenoma formation and can present in childhood. Familial adenomatous polyposis and Lynch syndrome are autosomal dominant, often with involvement of multiple family members, or can be seen in an individual arising from a de novo mutation. The most recently described adenomatous polyposis syndrome, MutYH-associated polyposis, is autosomal recessive, requiring an inherited mutation from each parent. All three adenomatous polyposis disorders can display tremendous variation in expression, even within the same family, and can have a common overlapping phenotype. These disorders require regular medical care to minimize cancer risk in the digestive tract and in other organ systems.