A novel and rapid method of determining the effect of unclassified MLH1 genetic variants on differential allelic expression.

Germline mutations in mismatch repair genes predispose patients to Lynch Syndrome and the majority of these mutations have been detected in two key genes, MLH1 and MSH2. In particular, about a third of the missense variants identified in MLH1 are of unknown clinical significance. Using the PeakPicker software program, we have conducted a proof-of-principle study to investigate whether missense variants in MLH1 lead to allelic imbalances. Lymphocyte RNA extracted from patients harboring known MLH1 variants was used to quantify the ratio of variant to wild-type transcript, while patient lymphocyte DNA was used to establish baseline allelic expression levels. Our analysis indicated that the missense variants c.350C>T, c.793C>T, and c.1852_1853AA>GC, as well as the truncating variant c.1528C>T were all associated with significantly unbalanced allelic expression. However, the variants c.55A>T and c.2246T>C did not demonstrate an allelic imbalance. These results illustrate a novel and efficient method to investigate the pathogenicity of unclassified genetic variants discovered in mismatch repair genes, as well as genes implicated in other inherited diseases. In addition, the PeakPicker methodology has the potential to be applied in the diagnostic setting, which, in conjunction with results from other assays, will help increase both the accuracy and efficiency of genetic testing of colorectal cancer, as well as other inherited diseases.

A novel complex mutation in MSH2 contributes to both Muir-Torre and Lynch Syndrome.

Mutations in mismatch repair genes lead to Lynch Syndrome, the most common form of inherited colorectal cancer. In this report, we describe a novel complex germline mutation c.[1601_1661+92dup; 1591_1611del] of the mismatch repair gene, MSH2. This mutation, which segregates with the disease phenotype, was discovered in a Lynch syndrome kindred that also shows a history of the Muir-Torre syndrome. Interestingly, several tumors from this family displayed microsatellite instability, a hallmark of Lynch syndrome tumors but no consistent, concomitant loss of MSH2 protein expression. In addition, a subset of tumors showed neither prototypical feature of microsatellite instability nor immunohistochemistry deficiency, highlighting the importance of a detailed molecular analysis of rare genetic alterations. This mutation and the atypical clinical manifestations observed underscore the genetic complexity underlying Lynch syndrome, and the importance of comprehensive molecular screening in the diagnosis and early detection of colorectal and other associated cancers.

A large novel deletion in the APC promoter region causes gene silencing and leads to classical familial adenomatous polyposis in a Manitoba Mennonite kindred.

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome caused by the inheritance of germline mutations in the APC tumour suppressor gene. The vast majority of these are nonsense and frameshift mutations resulting in a truncated protein product and abnormal function. While APC promoter hypermethylation has been previously documented, promoter-specific deletion mutations have not been reported. In a large Canadian Mennonite polyposis kindred, we identified a large novel germline deletion in the APC promoter region by linkage analysis and MLPA. By RT-PCR and sequence analysis, this mutation was found to result in transcriptional silencing of the APC allele. A few genetic disorders have been characterized as over-represented in the Manitoba Mennonite population, however, the incidence of cancer has not been recognized as increased in this population as compared to other Manitoba ethnic groups. This study strengthens the likelihood that this novel APC promoter mutation is linked to this unique population as a founder mutation.

Rh discrepancies caused by variable reactivity of partial and weak D types with different serologic techniques.

BACKGROUND: RhD discrepancies between current and historical results are problematic to resolve. The investigation of 10 discrepancies is reported here. STUDY DESIGN: Samples identified were those that reacted by automated gel technology and were negative with an FDA-approved reagent. Reactivity with a commercially available panel of monoclonal anti-D was performed. Genomic DNA was evaluated for RHD alleles with multiplex RHD exon polymerase chain reaction (PCR), weak D PCR-restriction fragment length polymorphism, and RHD exon 5 and 7 sequence analyses. RESULTS: The monoclonal anti-D panel identified two samples as DVa, yet possessed the DAR allele. Two weak D Type 1 samples had a similar monoclonal anti-D profile, but only one reacted directly with one of two FDA-approved anti-D. Only two of four weak D Type 2 samples reacted directly with one FDA-approved anti-D, and their D epitope profile differed. CONCLUSIONS: The monoclonal anti-D reagents did not distinguish between partial and weak D Types 1 and 2. Weak D Types 1 and 2 do not show consistent reactivity with FDA-approved reagents and technology. To limit anti-D alloimmunization, it is recommended that samples yielding an immediate-spin tube test cutoff score of not more than 5 (i.e., < or =1+ agglutination) or a score of not more than 8 (i.e., < or =2+ hemagglutination) by gel technology be considered D- for transfusion and Rh immune globulin prophylaxis. That tube test anti-D reagents react poorly with some Weak D Types 1 and 2 red cells is problematic, inasmuch as they should be considered D+ for transfusion and prenatal care. Molecular tests that distinguish common partial and Weak D types provide the solution to resolving D antigen discrepancies.

A Serum-Free System for Primary Cultures of Human Pituitary Adenomas.

We report the successful use of a serum-free culture system for primary cultures of human pituitary adenomas. The system utilizes histiotypic suspension culture with low protein-binding membrane inserts that enable cells to retain their three-dimensional tissue configuration, closely mimicking the growth pattern in vivo. A serum-free defined medium was developed with CMRL-1969 (Connaught, Willowdale, Ontario, Canada) supplemented with 0.375% albumin bovine Fraction V, 5 ug/mL insulin, 5 ug/mL transferrin, 5 ng/mL sodium selenite, 30 ug/mL putrescine, 6.85 x 10(11)M hydrocortisone, and 3.7 x 10'(11)Mtri-iodothyronine (T(3)). We analyzed eight surgically resected human pituitary adenomas. Basal pituitary hormone secretion measured by radioimmunoassay of pituitary hormones was compared with hormone hypersecretion in vivo and with control cells of the same tumors cultured in CMRL-1969 with 10% fetal calf serum. The light microscopic, immunocytochemical and ultrastructural morphology of cells cultured in this serum-free histiotypic system was compared with cells cultured in serum-supplemented media and with cells cultured on collagen-coated plastic; all cultured cells were compared with the morphology of surgically resected tissues of the same specimens. Basal pituitary hormone secretion during 24-hour incubations correlated with the clinical patterns of hormone excess; the data were similar in serum-enriched and serum-free cultures, however, hormone secretion decreased less rapidly in the serum-free cultures. Cells maintained in the histiotypic culture system closely resembled the corresponding surgically resected tumor using the morphologic parameters and were better preserved than those plated in collagen-coated plastic wells. This comparative study indicates that this serum-free histiotypic culture system provides an ideal method of examining pituitary adenomas in vitro without altering the profile of hormone secretion and cell morphology documented in vivo. This system can be used to examine the production and effects of a wide range of hormones and growth factors that have been implicated as causative agents in pituitary tumorigenesis.

Effects of somatostatin on somatotroph adenomas of the human pituitary: An in vitro functional and morphological study.

The effects of somatostatin or the somatostatin analog SMS 201-995 were studied on 4 densely granulated somatotroph adenomas and 4 sparsely granulated somatotroph adenomas in vitro. Release of growth hormone (GH) into culture media during incubation with somatostatin or SMS 201 -995 were measured by radioimmunoassay, and light-microscopical and ultrastructural morphometric parameters were compared with those of cultured control somatotroph adenoma cells of the same tumor. In all tumors except for 1 densely granulated somatotroph adenoma, somatostatin or SMS 201-995 decreased GH release into culture media in 24- and 2-hour incubations. After 48-hour incubation with somatostatin or SMS 201-995, there was no change in cell size or secretory granule diameter. One densely granulated adenoma showed decreased cytoplasmic volume density (CVD) of Golgi apparatus and secretory granules, and a sparsely granulated adenoma had reduced CVD of endoplasmic reticulum. All the tumors that responded with decreased GH release exhibited increased CVD of lysosomes after incubation with somatostatin or SMS 201-995. These results indicate that both densely and sparsely granulated somatotroph adenomas respond to somatostatin inhibition and, furthermore, that inhibition of hormone release is associated with accumulation of lysosomes, suggesting lysosomal degradation of stored hormone.