Whole-Exome Sequencing Identifies a Novel Homozygous Frameshift Mutation in the MTMR2 Gene as a Causative Mutation in a Patient with Charcot-Marie-Tooth Disease Type 4B1.

Charcot-Marie-Tooth (CMT) disease refers to a heterogeneous group of axonal and demyelinating polyneuropathies, characterized by chronic motor and sensory dysfunction. CMT is the most common genetic cause of neuropathy. The present study aimed to identify the gene mutation responsible for CMT in Ashkenazi Jew (AJ) patient. Genomic DNA was extracted from whole blood leukocytes of affected family and normal subject. Whole-exome sequencing was performed using the Illumina HiSeq2500. The DNA region containing the identified mutation was amplified by PCR and sequenced using dye-terminator chemistry and the forward primer. Physical examination of the patient revealed weakness and atrophy of the lower extremity muscles and Pes cavus foot deformity. Whole-exome sequencing indicated that the patient is homozygous for a novel frameshift mutation (c.1877_1878insAGAG, p.Arg630fs) in the myotubularin-related protein-2 gene (MTMR2), which resulted in an erroneous C-terminal sequence and extension by 15 amino acids. Patients' parents are healthy, and DNA sequencing analysis indicated that both are heterozygotes to the described mutation. The clinical feature of the patient may indicate a complete co-segregation of the p.Arg630fs mutation in MTMR2 gene with the CMT type 4B1 phenotype. Further studies are needed in order to estimate the prevalence of this mutation among AJ.

Impaired light chain allelic exclusion and lack of positive selection in immature B cells expressing incompetent receptor deficient of CD19.

Positive signaling is now thought to be important for B cell maturation, although the nature of such signals has not yet been defined. We are studying the regulatory role of B cell Ag receptor (BCR) signaling in mediating positive selection of immature B cells. To do so, we use Ig transgenic mice (3-83Tg) that are deficient in CD19, thus generating a monoclonal immature B cell population expressing signaling-incompetent BCR. Immature 3-83Tg CD19(-/-) B cells undergo developmental arrest in the bone marrow, allowing maturation only to cells that effectively compensate for the compromised receptor by elevated levels of BCR. We find that developmentally arrested 3-83Tg CD19(-/-) B cells fail to impose L chain allelic exclusion and undergo intensive V(D)J recombination to edit their BCR. Furthermore, immature 3-83Tg CD19(-/-) B cells, which were grown in vitro, failed to undergo positive selection and to survive when adoptively transferred into normal recipients. However, elevation of BCR expression levels, obtained by transgene homozygosity, effectively compensated for the compromised BCR and completely restored BCR-mediated Ca(2+) influx, allelic exclusion, and positive selection. Our results suggest that the BCR signaling threshold mediates positive selection of developing B cells, and that a receptor-editing mechanism has an important role in rescuing cells that fail positive selection because of incompetent receptors.

Increased expression of matrix metalloproteinase-2: a diagnostic marker but not prognostic marker of papillary thyroid carcinoma.

BACKGROUND: Matrix metalloproteinases are proteolytic enzymes that degrade extracellular matrix components. Numerous studies have demonstrated that individual MMPs play a crucial role in tumor invasion and metastasis. OBJECTIVE: To examine the expression of MMPs and their inhibitor TIMP-2 in neoplastic and normal thyroid tissues. METHODS: We examined 33 cases of thyroid tumor (papillary, follicular and medullary carcinoma, follicular adenoma and multinodular goiter). MMP protein content and activity were measured by enzyme-linked immunosorbent assay and gel zymography. Immunohistochemistry was also performed. RESULTS: The thyroid tissues examined secreted MMP-2 and 9 as well as TIMP-2, but only MMP-2 was significantly higher in papillary carcinoma cases compared to the adjacent normal tissue or to the other tumor entities. Increased MMP-2 immunohistochemical staining was demonstrated in the neoplastic papillary epithelial component. No significant difference was seen between papillary carcinomas with lymph node metastases and those without. CONCLUSIONS: Increased MMP-2 expression may be useful as a diagnostic marker to differentiate papillary carcinoma from other thyroid neoplasms, but it cannot serve as a useful prognostic marker.