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.

Further evidence for heritability of an epimutation in one of 12 cases with MLH1 promoter methylation in blood cells clinically displaying HNPCC.

Germline mutations in mismatch repair (MMR) genes, tumours with high microsatellite instability (MSI-H) and loss of MMR protein expression are the hallmarks of HNPCC (Lynch syndrome). While somatic MLH1 promoter hypermethylation is generally accepted in the tumorigenesis of sporadic tumours, abnormal MLH1 promoter methylation in normal body cells is controversially discussed as a mechanism predisposing patients to HNPCC. In all 94 patients suspected of HNPCC-syndrome with a mean age of onset of 45.5 years, MLH1-deficiency in their tumours but no germline mutation, underwent methylation-specific PCR-screening for MLH1 promoter methylation. In peripheral blood cells of 12 patients an MLH1 promoter methylation, in seven informative cases allele-specific, was found. Normal colonic tissue, buccal mucosa, and tumour tissue available from three patients also presented abnormal methylation in the MLH1 promoter. The heredity of aberrant methylation is questionable. Pro: MLH1 promoter methylation was found in a patient and his mother giving evidence for a familial predisposition for an epimutation in MLH1. Contra: a de novo set-up of methylation in one patient, a mosaic or incomplete methylation pattern in six patients, and no evidence for inheritance of MLH1 promoter methylation in the remaining families. Our findings provide strong evidence that MLH1 promoter methylation in normal body cells mimics HNPCC and constitutes a pathogenic pre-lesion in MLH1. The identification of hypermethylation as an epigenetic defect has important implications for surveillance recommendations, as these patients should be treated like Lynch syndrome patients, whereas the heritability of methylation is still under investigation.

Compound heterozygosity for two MSH6 mutations in a patient with early onset colorectal cancer, vitiligo and systemic lupus erythematosus.

Lynch syndrome (hereditary non-polyposis colorectal cancer, HNPCC) is an autosomal dominant condition caused by heterozygous germline mutations in the DNA mismatch repair (MMR) genes MLH1, MSH2, MSH6, or PMS2. Rare cases have been reported of an inherited bi-allelic deficiency of MMR genes, associated with multiple café-au-lait spots, early onset CNS tumors, hematological malignancies, and early onset gastrointestinal neoplasia. We report on a patient with vitiligo in segments of the integument who developed systemic lupus erythematosus (SLE) at the age of 16, and four synchronous colorectal cancers at age 17 years. Examination of the colorectal cancer tissue showed high microsatellite instability (MSI-H) and an exclusive loss of expression of the MSH6 protein. Immunohistochemical analysis of normal colon tissue also showed loss of MSH6, pointing to a bi-allelic MSH6 mutation. Sequencing of the MSH6 gene showed the two germline mutations; c.1806_1809delAAAG;p.Glu604LeufsX5 and c.3226C > T;p.Arg1076Cys. We confirmed that the two mutations are on two different alleles by allele-specific PCR. To our knowledge, neither parent is clinically affected. They did not wish to be tested for the mutations identified in their daughter. These data suggest that bi-allelic mutations of one of the MMR genes should be considered in patients who develop early-onset multiple HNPCC-associated tumors and autoimmune disorders, even in absence of either hematological malignancies or brain tumors.

Towards mapping phenotypical traits in 18p- syndrome by array-based comparative genomic hybridisation and fluorescent in situ hybridisation.

Molecular karyotyping holds the promise of improving genotype-phenotype correlations for frequent chromosome conditions such as the 18p- syndrome. In spite of more than 150 reported cases with deletions in 18p, no reliable phenotype map for the characteristic clinical findings such as mental retardation, post-natal growth retardation and typical facial features has been established yet. Here, we report on four patients with partial monosomy 18p of different sizes owing to unbalanced translocations that were thoroughly characterised clinically and by molecular karyotyping. One patient had a terminal deletion of 1.6 Mb in 18p and a trisomy of 8q24.23-qter as determined by array-based comparative genomic hybridisation and large insert clone fluorescent in situ hybridisation. In two sibs and a fourth patient, cytogenetic and molecular-cytogenetic analyses showed the terminal deletions in 18p (8.0 and 13.84 Mb, respectively) to be accompanied by partial trisomies of 20p. Literature analyses of typical phenotypic features of 18p-, 8q+ and 20p+ syndromes allowed the attribution of clinical findings in our patients to the respective chromosomal aberration. Based on these data, we propose a phenotype map for several clinical features of the 18p- syndrome: Round face was tentatively mapped to the distal 1.6 Mb of 18p; post-natal growth retardation and seizures to the distal 8 Mb and ptosis and short neck to the proximal half of 18p.

Nine novel pathogenic germline mutations in MLH1, MSH2, MSH6 and PMS2 in families with Lynch syndrome.

Many germline mutations in the DNA mismatch repair genes have been described so far leading to the clinical phenotype of Lynch syndrome (hereditary nonpolyposis colorectal cancer, HNPCC). Most mutations are private mutations. We report on nine novel pathogenic germline mutations that have been found in families meeting either the Amsterdam or the Bethesda criteria. These findings include the mutations MLH1,c.884+4A>G, MLH1,c.1377_1378insA;p.Glu460ArgfsX19, MLH1,c.1415_1416delGA;p.Arg472ThrfsX5, MSH2,c.301G>T;p.Glu101X, MSH2,c.638_639delTG;p.Leu213GlnfsX18, MSH2,c.842C>A;p.Ser281X, MSH2,c.859G>T;p.Gly287X, MSH6,c.2503C>T;p.Gln835X and a large genomic deletion of exons 1-10 of the PMS2 gene. The mutation MLH1,c.884+4A>G detected in two families results in a complete skipping of exon 10 on mRNA level and thus has been considered as pathogenic. In all cases the tumor tissue of the index patient revealed high microsatellite instability (MSI-H) and showed a complete loss of expression of the affected protein in the tumor cells by immunohistochemistry (IHC). The findings underline the importance of a pre-screening of tumor tissue for an efficient definition of conspicuous cases.