DNMT1 mutations found in HSANIE patients affect interaction with UHRF1 and neuronal differentiation

DNMT1 is recruited to substrate sites by PCNA and UHRF1 to maintain DNA methylation after replication. The cell cycle dependent recruitment of DNMT1 is mediated by the PCNA-binding domain (PBD) and the targeting sequence (TS) within the N-terminal regulatory domain. The TS domain was found to be mutated in patients suffering from hereditary sensory and autonomic neuropathies with dementia and hearing loss (HSANIE) and autosomal dominant cerebellar ataxia deafness and narcolepsy (ADCA-DN) and is associated with global hypomethylation and site specific hypermethylation. With functional complementation assays in mouse embryonic stem cells, we showed that DNMT1 mutations P496Y and Y500C identified in HSANIE patients not only impair DNMT1 heterochromatin association, but also UHRF1 interaction resulting in hypomethylation. Similar DNA methylation defects were observed when DNMT1 interacting domains in UHRF1, the UBL and the SRA domain, were deleted. With cell-based assays, we could show that HSANIE associated mutations perturb DNMT1 heterochromatin association and catalytic complex formation at methylation sites and decrease protein stability in late S and G2 phase. To investigate the neuronal phenotype of HSANIE mutations, we performed DNMT1 rescue assays and could show that cells expressing mutated DNMT1 were prone to apoptosis and failed to differentiate into neuronal lineage. Our results provide insights into the molecular basis of DNMT1 dysfunction in HSANIE patients and emphasize the importance of the TS domain in the regulation of DNA methylation in pluripotent and differentiating cells.

B Cell Lymphoma: A Case With Localized Involvement of the Prostate on F-18-FDG Examination

An 80-year-old man had symptoms of urinary retention. Biopsy of the prostate revealed B cell lymphoma. To evaluate the extent of the disease, an F-18 FDG study was performed with positron emission tomography/computed tomography (CT). One hour after intravenous administration of 18.5 mCi F-18 FDG, imaging was carried out from the skull base to the upper thigh. An area of moderately increased activity was noted within the prostate bed. A noncontrast CT, for attenuation correction and anatomic localization, revealed maintenance of fat planes around the prostate, indicating disease localized to that organ. Hence, a B cell lymphoma had been localized to the prostate.

Asymmetric Tongue Muscle Uptake of F-18 FDG

A 58-year-old woman, with nonsmall cell carcinoma, had multiple metastasis on 2-F-18 FDG positron emission tomography imaging. The right hemitongue had increased activity as compared with the left. This was not the result of the presence of a metastasis to the tongue, as shown by a negative computed tomography scan of the region and failure to demonstrate a lesion over a period of weeks. Uptake was likely related to right hemiglossal muscle activity. This was made more apparent by decreased uptake on the opposite side of the tongue (up to the midline) as a result of left cranial nerve XII paralysis.

Supine versus prone injection of Tc-99m MAA: evidence of thoracic compression or fluid shift

After a cesarean section, a woman had sharp left chest pain that radiated to the arm and was worse with inspiration. A chest radiograph revealed minimal left lung base atelectasis. A total of 5 mCi (185 mBq) Tc-99m macroaggregated albumin (MAA) was injected with the patient supine. A posterior oblique perfusion lung image revealed nearly absent perfusion of the left lung base. The patient was then injected with an equal quantity of Tc-99m MAA while prone. Images now demonstrated perfusion of the left lower lung. This might represent redistribution of fluid obscured by the atelectatic area, or the relief of pressure on pulmonary arteries to the left lower lobe by positional change.

Cytogenetic changes in Wilms' tumors

Cytogenetic analysis of 20 Wilms' tumors using short-term culture techniques were undertaken. Chromosome abnormalities were detected in all tumors. In 19 of 20 cases only minor karyotypic changes were observed within cells with near-diploid chromosome numbers; only one tumor was predominantly hyperdiploid. Rearrangements involving chromosome 1 were the most frequently observed abnormality (in 25%) and often resulted in partial or complete trisomy for the long arm. In 20% of the tumors, abnormalities involving chromosomes 11 and 16 were present. The only other chromosomes frequently involved in structural or numerical changes were #12, and #18. Two discrete tumor foci within the same kidney differed cytogenetically, suggesting an independent origin for each focus. No correlation could be made between specific chromosome abnormalities and tumor stage or histologic subtype. Although constitutional deletion of chromosome region 11p13 has frequently been reported to predispose to Wilms' tumor formation, only two tumors with deletions involving this region were observed. Chromosomes from tumors treated with chemotherapy prior to surgical removal and culture yielded findings similar to those in untreated tumor cells.