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Mutations in the THAP1 gene have recently been identified as the cause of DYT6 primary dystonia. However, the changes in THAP1 gene function and in the microstructure of brain white matter have not been well-characterized.Four different mutations of THAP1 expression (clones F22fs71X, C54F, F25fs53X, and L180S) were transfected into HEK-293T cells. The subcellular distribution of THAP1 in each clone was identified using immunofluorescence microscopy and Western blot. Six patients who harbored these THAP1 mutations underwent diffusion tensor magnetic resonance imaging (DTI) of the brain. The fractional anisotropy (FA) and mean diffusivity (MD) were measured in twenty-four regions of interest (ROI).In two truncated mutations (F22fs71X and F25fs53X), the subcellular distribution of THAP1 were both in the cytoplasm and nucleus. However, the subcellular distribution was detected almost in the nucleus in two missense mutations (C54F and L180S). In the DTI maps, the average values of fractional anisotropy (FA), a measure of axonal integrity and coherence, was reduced (p 0.005) in the subgyral white matter of the sensorimotor cortex of the DYT1 carriers, comparing with controls.Truncated THAP1 mutations (F22fs71X and F25fs53X) can alter the subcellular distributions, while some missense mutation (C54F and L180S) can not. The axonal integrity and coherence in the region of sensorimotor area of the brain was damaged in DYT6 dystonia.

Mutations in the THAP1 gene were recently identified as the cause of DYT6 primary dystonia. More than 40 mutations in this gene have been described in different populations. However, no previous report has identified sequence variations that affect the transcript process of the THAP1 gene. In addition, the mutation frequency in Chinese early-onset primary dystonia has not been well characterized. One hundred and two unrelated patients with non-DYT1 early-onset primary dystonia (age at onset26 years), family members of participants with mutations, and 200 neurologically normal controls were screened for THAP1 gene mutations. The effects of the identified mutations on RNA expression were analyzed using semi-quantitative real-time PCR. Seven sequence variants (c.63_66del TTTC, c.161GT, c.224AT, c.267GA, c.339TC, c.449AC, and c.539TC) were identified in this group of patients (6.9%). In this cohort, 15 subjects (seven unrelated patients and eight family members) were detected to have THAP1 sequence variants. Among these 15 subjects, 11 were manifested (penetrance of DYT6 was 73.3%) and seven presented with craniocervical involvement (63.6%). However, one patient manifested paroxysmal headshake, and one presented with essential hand tremor. Semi-quantitative real-time PCR indicated that a novel silent mutation (c.267GA) decreased the expression of THAP1 in human lymphocytes. Our findings indicated that THAP1 sequence variants are not common in non-DYT1 early-onset primary dystonia in China and that the clinical manifestation may vary. One silent mutation (c.267GA) was shown to affect THAP1 expression.

Context: The molecular pathogenesis of sporadic insulinomas is unknown. There is a lack of biomarker to distinguish benign and malignant form of insulinoma. Objective: Our objective was to confirm the occurrence of microsatellite instability (MSI) in insulinomas, to identify alterations of mismatch repair (MMR) genes in the tumors, and to evaluate the possibility to distinguish benign and malignant insulinoma or to predict the clinical outcome of patients with these alterations. Design and Patients: We detected MSI and inactivation of MLH1 gene in 55 sporadic insulinomas by PCR, immunohistochemical staining, allelic typing, analysis of promoter methylation, and exon mutations. Their correlations with clinicopathological characteristics were analyzed with univariate and multivariate statistic analysis. Results: A high rate of MSI (MSI-H) was found in 33% of sporadic insulinomas. Reduced expression of mutL homolog 1 (MLH1) protein was observed in 36% of insulinomas and correlated with MSI-H (P = 0.008). Promoter methylation and loss of heterozygosity of MLH1 gene was found in 31 and 49% of insulinomas, respectively. Reduced expression of MLH1 and MSI-H were significantly associated with both tumor malignancy (P = 0.033 and P = 4.8 × 10−6, respectively) and incurable disease (P = 0.006 and P = 0.001, respectively). Conclusion: High frequency of MSI occurred in sporadic insulinomas. The silencing of MLH1 gene may partially contribute to the MSI-H in the tumors. Assessing MSI-H and expressions of MLH1 could be used to distinguish benign and malignant insulinomas and to predict the outcome of patients. Detecting of a high rate of microsatellite instability can be used to distinguish malignancy from benign, and predict clinical outcome of the sporadic insulinomas.

The pathogenesis of sporadic insulinomas is not clear, and there are no reliable genetic determinants that are useful to distinguish malignant and benign forms of this tumor. It was reported that 1q LOH might contribute to pathogenesis in gastrinomas and was correlated with tumor progression. However, little data are available on 1q LOH in sporadic insulinomas. In our study, we determine whether 1q LOH occurs in sporadic insulinomas and is associated with tumor malignancy by performing 1q allelotyping with 17 markers in 40 tumors and pair normal DNA. Thirty-five (88%) insulinomas had 1q LOH. Of the 35 insulinomas with 1q LOH, 14 (40%) had 1q21.3-23.2 LOH over a 7.5 cM region (SRO-1), whereas LOH in 21 tumors (60%) occurred at 1q31.3 over an 11.4 cM area (SRO-2). Of 24 tumors without MEN1 LOH, 20 had either SRO-1 or SRO-2 LOH (83%), whereas in 16 tumors with MEN1 LOH, 9 were shown to have LOH at either SRO-1 or SRO-2 (56%) (p = 0.065). This result suggests that LOH at 2 SRO might be MEN1 gene independent and may contribute to the pathogenesis in a subset of insulinomas without MEN1 gene LOH. The presence of 1q21.3-23.2 LOH is significantly associated with malignancy of insulinomas (p = 0.014). The high frequency of LOH at 1q 21.3-23.2 and 1q31.3 suggests these 2 areas may harbor putative tumor suppressor genes that may play an important role in the tumorigenesis of a subset of insulinomas. LOH at 1q21.3-23.2, which was associated with tumor malignancy, could be one of the genetic markers for identifying malignancy in sporadic insulinomas.