Muir-Torre syndrome

Muir-Torre syndrome is an autosomal-dominant skin condition of genetic origin, characterised by tumours of the sebaceous gland or keratoacanthoma that are associated with visceral malignant diseases. The cutaneous characteristics of Muir-Torre syndrome are sebaceous adenoma, epithelioma, carcinoma, or multiple keratoacanthomas, whereas visceral malignant diseases include colorectal, endometrial, urological, and upper gastrointestinal tumours. Although Muir-Torre syndrome has a striking familial association and features of autosomal-dominant transmission, it can arise in individuals without a family history or any known mutations. Clinical and biomolecular evidence has suggested that there are two types of Muir-Torre syndrome. The most common is a variant of hereditary non-polyposis colorectal cancer, which is characterised by defects in mismatch repair genes and early-onset tumours. The second type does not show deficiency in mismatch repair and its pathogenesis remains undefined. Diagnosis of these rare sebaceous lesions warrants the search for associated internal malignant diseases: the peculiarity of skin lesions and their biomolecular characterisation with microsatellite instability analysis and immunohistochemistry could be used to identify familial Muir-Torre syndrome, allowing clinicians to tailor a personalised programme to screen for skin and visceral malignant diseases in high-risk individuals.

DNA differential diagnosis of human taeniid cestodes by base excision sequence scanning thymine-base reader analysis with mitochondrial genes

For DNA differential diagnosis of human Taenia cestodes, a base excision sequence scanning thymine-base method using the cytochrome c oxidase subunit I and cytochrome b genes as targets was used. The characteristic thymine-base peak profiles provide four distinct types, unique for T. saginata, T. asiatica, and two genotypes of T. solium. This approach provides a useful tool for the identification and diagnosis of human taeniid cestodes without DNA sequencing if nucleotide sequence databases are available.

Functional analysis of hMLH1 variants and HNPCC-related mutations using a human expression system

BACKGROUND & AIMS

Germline mutations in the DNA mismatch repair (MMR) genes hMLH1 and hMSH2 are associated with susceptibility to hereditary nonpolyposis colorectal cancer (HNPCC). Because a significant proportion of hMLH1 mutations are missense, the assessment of their pathogenic role may be difficult. To date, functional analysis of missense mutations has been performed primarily in Saccharomyces cerevisiae. The aim of this study was to examine the biochemical properties of hMLH1 protein variants in a human expression system.

METHODS

The HNPCC-related hMLH1 mutations T117M, V185G, R217C, G244D, R265C, V326A, and K618T, the polymorphisms I219V and R265H, and a hMLH1 splicing variant lacking exon 9 and 10 (hMLH1 Delta 9/10) were cloned. On transfection of these constructs into human 293T cells, which do not express hMLH1 because of promoter hypermethylation, the hMLH1 protein variants were analyzed by Western blotting and in a MMR assay.

RESULTS

Transfection was successful for all hMLH1 constructs. As anticipated, the mutations K618T and T117M, which affect the highly conserved domains of hMLH1 that are necessary for interaction with hPMS2 or for adenosine triphosphate (ATP) binding, respectively, affected protein stability or its ability to complement MMR-deficient 293T-cell extracts. The V185G, G244D, and Delta 9/10 variants were also unable to complement MMR in 293T cells, whereas hMLH1 proteins carrying the I219V, R265H, R265C, R217C, and V326A mutations were MMR competent.

CONCLUSIONS

These data show that the pathogenic role of hMLH1 missense mutations and splicing variants can be assessed by analyzing the biochemical properties of their protein products in a homologous expression system.