Biomedical subjects

R Chen

Publications and source records attributed to R Chen.

At least 19 recordsLinked to original sources

PubMed2026

Development of RS1-specific ACMG/AMP variant classification criteria with pilot variant curation.

Gene-based therapies are being developed for retinal diseases, including RS1-related X-linked retinoschisis. Therefore it is essential to determine which variants are pathogenic and which are benign when enrolling patients. The Clinical Genome Resource (ClinGen) X-Linked Inherited Retinal Diseases (XLRD) Variant Curation Expert Panel (VCEP) brings together clinician scientists, molecular biologists, and geneticists to apply their expertise and review the clinical, genetic, population, and functional evidence for variants. American College of Medical Genetics (ACMG) guidelines have been modified for RS1 to develop a highly systematic and conservative framework for evaluating variants. The curation process involves applying 28 different codes, each with 4 strength levels (very strong, strong, moderate, supporting) across different domains of phenotype, population data, computational assessment, functional impact, and segregation. With RS1-specific rules, a total of 54 pilot variants were tested. These included 47 variants in ClinVar. Of these 21 variants were re-classified: 2 likely pathogenic variants and one likely benign were changed to variants of uncertain significance and 4 previously unclassified variants were changed to pathogenic, likely pathogenic and likely benign. Other changes resolved conflicts or multiple classifications.

Humans↗

PubMed2025

HLA-E and NKG2A Mediate Resistance to BCG Immunotherapy in Non-Muscle-Invasive Bladder Cancer.

Bacillus Calmette-Guérin (BCG) is the first-line therapy for high-grade non-muscle-invasive bladder cancer (NMIBC), yet many patients experience recurrence due to immune evasion. We identify HLA-E and NKG2A as mediators of adaptive resistance involving chronic activation of NK and T cells in BCG-unresponsive tumors. Prolonged IFN-γ exposure enhances HLA-E and PD-L1 expression on recurrent tumors, accompanied by the accumulation of NKG2A+ NK and CD8 T cells. HLA-Ehigh tumor cells preferentially cluster near CXCL12-rich stromal regions with dense effector cell presence, underscoring a spatially segregated tumor architecture. Although cytotoxic lymphocytes retain effector potential, their activity is restrained by HLA-E/NKG2A and PD-L1/PD-1 pathways located in their immediate neighborhood within the bladder tumor microenvironment. These data reveal a spatially organized immune escape program that limits anti-tumor immunity. Our findings support dually targeting NKG2A and PD-L1 checkpoint blockade as a rational, bladder-sparing strategy for patients with BCG-unresponsive NMIBC.

BCG-unresponsive↗

PubMed1998

Mechanisms of cortical reorganization in lower-limb amputees.

The human motor system undergoes reorganization after amputation, but the site of motor reorganization and the mechanisms involved are unknown. We studied the site and mechanisms of motor reorganization in 16 subjects with traumatic lower-limb amputation. Stimulation at different levels in the CNS was used to determine the site of reorganization. The mechanisms involved were evaluated by measuring the thresholds for transcranial magnetic stimulation (TMS) and by testing intracortical inhibition and facilitation. With TMS, the threshold for muscle activation on the amputated side was lower than that of the intact side, but with transcranial electrical stimulation there was no difference in motor threshold between the two sides. TMS at the maximal output of the stimulator activated a higher percentage of the motor neuron pool (%MNP) on the amputated side than on the intact side. The %MNP activated by spinal electrical stimulation was similar on the two sides. Paired TMS study showed significantly less intracortical inhibition on the amputated side. Our findings suggest that motor reorganization after lower-limb amputation occurs predominately at the cortical level. The mechanisms involved are likely to include reduction of GABAergic inhibition.

Adult↗

PubMed1998

Antibacterial agents that inhibit two-component signal transduction systems.

A class of antibacterials has been discovered that inhibits the growth of Gram-positive pathogenic bacteria. RWJ-49815, a representative of a family of hydrophobic tyramines, in addition to being a potent bactericidal Gram-positive antibacterial, inhibits the autophosphorylation of kinase A of the KinA::Spo0F two-component signal transduction system in vitro. Analogs of RWJ-49815 vary greatly in their ability to inhibit growth of bacteria and this ability correlates directly with their activity as kinase A inhibitors. Compared with the potent quinolone, ciprofloxacin, RWJ-49815 exhibits reduced resistance emergence in a laboratory passage experiment. Inhibition of the histidine protein kinase::response regulator two-component signal transduction pathways may present an opportunity to depress chromosomal resistance emergence by targeting multiple proteins with a single inhibitor in a single bacterium. Such inhibitors may represent a class of antibacterials that potentially may represent a breakthrough in antibacterial therapy.

Anti-Bacterial Agents↗

PubMed1998

Regulated expression of mature human insulin in the liver of transgenic mice.

Transgenic mice expressing either human proinsulin cDNA or mutated proinsulin cDNA in the liver were created. The human proinsulin cDNA was mutated to generate a protein cleavable by the ubiquitous prohormone convertase furin, thus leading to mature insulin peptide. All transgenic lines expressed human C-peptide in the blood, whose level varied according to nutritional conditions. High performance liquid chromatography fractionation of mouse serum revealed that mutant proinsulin was effectively processed into mature insulin in vivo. This transgenic mouse model provides a useful tool for further prospects of gene therapy of insulin-dependent diabetes mellitus.

Animals↗

PubMed1998

Molecular cloning of human homolog of yeast GAA1 which is required for attachment of glycosylphosphatidylinositols to proteins.

Anchoring proteins to cell surface membranes by glycosylphosphatidylinositols (GPIs) is important. We have isolated a component of the putative transamidase machinery, hGaa1p (human GPI anchor attachment protein). hGAA1 cDNA is approximately 2 kb in length and codes 621 amino acids. The amino acid sequence of hGaa1p is 25%, identical and 57% homologous to that of yeast Gaa1p. Moreover, Kite-Dolittle hydrophobicity plots of both proteins show marked similarity. hGAA1 gene is expressed ubiquitously and mRNA levels are higher in the undifferentiated state. Overexpression of antisense hGAA1 in human K562 cells significantly reduced the production of a reporter GPI-anchored protein.

Amino Acid Sequence↗

PubMed1998

Demonstration of dose-dependent global and regional cocaine-induced reductions in brain blood flow using a novel approach to quantitative single photon emission computerized tomography.

Ischemic stroke is a common cause of morbidity and mortality in cocaine addicts. Because the previous semiquantitative single photon emission computerized tomography (SPECT) method for measuring brain blood flow does not quantify blood flow, the magnitude and specificity of cocaine's effects during drug taking has not been well established. Here, using a novel quantitative approach to SPECT, we established that intravenous cocaine administration to nine recently abstinent cocaine-dependent subjects was associated with significant decreases in global and regional brain blood flow to dopamine-rich areas such as the prefrontal, frontal temporal, and subcortical gray matter. Establishing the utility of this relatively new quantitative SPECT technique provides an important tool for the management of vascular disorders of the brain. Additionally, identifying the site-specific effects of cocaine provides targets for the development of putative therapeutic medications to attenuate or minimize ischemic stroke in cocaine addicts.

Adolescent↗

PubMed1998

Comparative clinical study of inhaled beclomethasone dipropionate and triamcinolone acetonide in persistent asthma.

UNLABELLED: At this time, no placebo-controlled studies in the clinical literature compare the efficacy and safety of the most widely prescribed oral inhaled corticosteroids when dosed at their recommended daily doses. This study compared the efficacy and safety of beclomethasone dipropionate (BDP) 336 microg/day administered by metered dose inhaler (MDI) alone, and triamcinolone acetonide (TA) 800 microg/day by MDI with a built-in tube extender in adults with persistent asthma. METHODS: This 56-day, randomized, double-blind, double-dummy, placebo-controlled, multicenter trial was conducted in 328 adults with mild to moderately severe asthma (FEV1 50% to 90% of predicted while maintained on inhaled corticosteroids). Patients were seen at a baseline visit and on study days 28 and 56. Efficacy variables included pulmonary function tests, physician and patient assessments of asthma condition, and use of rescue medication. RESULTS: Statistically significant improvements from baseline in most efficacy measures were demonstrated for both active treatments versus placebo, and with the following exception were the same between active treatments: mean increase in FEV1 in the beclomethasone dipropionate group was statistically significantly greater than in the triamcinolone acetonide group on day 28. Throughout the study, BDP was statistically superior to TA with respect to mean change from baseline in total asthma symptom scores and for 3 of 8 weeks in reducing the mean average weekly use of rescue albuterol (the two active treatments were comparable for this variable at all other time points). Beclomethasone dipropionate and TA were comparable in safety. CONCLUSION: In adult patients with mild to moderately severe persistent asthma, treatment with BDP consistently conferred greater improvement from baseline in mean FEV1 than TA. This difference achieved statistical significance after 28 days of therapy but was not maintained to endpoint. Decreases in overall asthma symptom scores and in the use of rescue albuterol were statistically significantly greater for the BDP group compared with the TA group. Based on these findings, we conclude that BDP is at least as effective as TA in the treatment of persistent asthma in adults, and judged by some measures, may be superior.

Administration, Inhalation↗

PubMed1998

Electrophysiological studies in the critical care unit: investigating polyneuropathies.

Polyneuropathies frequently contribute to ventilator dependency and prolonged stay in the intensive care unit. As clinical examination is often limited in critically ill patients, electrophysiological studies are invaluable in establishing the diagnosis of neuropathy, determining its pathophysiology, severity and in following the patients' progression. Guillain-Barré syndrome (GBS) developing before intensive care unit admission and critical illness polyneuropathy (CIP) developing as a complication of sepsis and multiorgan failure are the commonest causes of neuropathy. Electrophysiological findings in CIP are that of an axonal neuropathy whereas the findings in GBS are usually consistent with a demyelinating neuropathy. Axonal GBS can be distinguished from CIP by the preceding illnesses, slow nerve conduction velocity in some cases, lack of spontaneous activity on the initial needle electromyographic study and cerebrospinal fluid findings.

Critical Illness↗

PubMed1998

Clinical correlates of hypertensive end-stage renal disease.

Although there has been much discussion regarding the etiology of hypertensive renal disease, clinical characteristics of this condition have not been thoroughly studied. The purpose of this investigation was to identify clinical correlates of hypertensive end-stage renal disease (ESRD) in a population of patients older than 50 years and to compare these clinical findings with those in a group of ESRD patients with certain known disorders (established diagnoses). Data regarding demographics, cause of ESRD, educational level, presence of diabetes mellitus, angina, myocardial infarction, and peripheral vascular disease were obtained from the Southeastern Kidney Council for patients starting renal replacement therapy between January 1, 1990, and August 1, 1996. Clinical characteristics were compared for white and black patients. Demographic variables and comorbid conditions were compared between groups with general linear regression or logistic regression contrast techniques. A logistic regression model was formed with hypertensive ESRD or established diagnoses as the outcome variable and comorbid and socioeconomic variables as the independent variables. Hypertensive ESRD was diagnosed in 24% of white and 38% of black patients, while established diagnoses were present in 17% of white and 7% of black ESRD patients. The most common established diagnoses were polycystic kidney disease, specified glomerulonephritis, and nephrolithiasis or obstruction. In a logistic regression model, white patients were found more likely to be classified as having hypertensive ESRD if they were older, suffered from angina and other forms of atherosclerosis, smoked, and were less educated. White patients with hypertensive ESRD were more than 2.4 times as likely to suffer from angina as patients with established diagnoses. For black patients, the presence of peripheral vascular disease and female gender were associated with an increased chance of being diagnosed as having hypertensive ESRD. The results of this investigation show that there is a strong association between atherosclerosis and hypertensive ESRD in older white patients. In black patients, the association between atherosclerosis and hypertensive ESRD was also present, but not as strong. The unique association of hypertensive ESRD with atherosclerosis suggests that atherosclerosis is a risk factor for chronic renal failure and that a primary renal microvascular disorder may lead to both hypertension and progressive renal insufficiency.

Age Factors↗

PubMed1998

Positron emission tomography [15O]water studies with short interscan interval for single-subject and group analysis: influence of background subtraction.

Use of short interscan interval [15O]water positron emission tomography (PET) studies reduces the overall study duration and may allow an increased number of scans for single-subject analysis of unique cases (e.g., stroke). The purpose of this study was to examine how subtraction of residual radioactivity from the previous injection (corrected scan) compared to nonsubtraction (uncorrected scan) in a PET short interscan interval (6 minutes) study affects single-subject and group data analysis using a motor activation task. Two currently widely used analytic strategies, Worsley's method and the SPM technique, were applied. Excellent agreement between activation maps obtained from corrected and uncorrected data sets was obtained both in single-subject analyses performed on data sets from the six normal subjects and three stroke (subcortical infarct) patients, and in group analysis (six normal subjects) within a particular statistical method. The corrected and uncorrected data were very similar in the (1) number of activated brain regions; (2) size of clusters of activated brain voxels; (3) Talairach coordinates of the activated region; and (4) t or Z value of the peak intensity for every significantly activated motor brain structure (both for large activations such as in motor cortex and small activations such as in putamen and thalamus). [15O]Water PET data obtained with a short interscan interval (6 minutes) produce similar results whether or not the background is subtracted. Thus, if injection dose and timing are constant, one can achieve the advantage of a short interscan interval without the added complexity of correcting for background radioactivity.

Adult↗

PubMed1998

Phenytoin does not influence postexercise facilitation of motor evoked potentials.

Postexercise facilitation of motor evoked potentials (MEPs) elicited to transcranial magnetic stimulation occurs after brief, nonfatiguing muscle activation. This phenomenon may be related to post-tetanic potentiation or long-term potentiation (LTP) observed in animal studies. Phenytoin reduces post-tetanic potentiation but does not block LTP. We studied the effects of phenytoin on postexercise MEP facilitation and its decay over time. Phenytoin did not result in either significant change in postexercise MEP facilitation nor significant change in the decay of facilitation. We conclude that postexercise MEP facilitation is unlikely to be secondary to post-tetanic potentiation.

Adult↗

PubMed1998

Analysis of data associated with seemingly temporal clustering of a rare disease.

Three statistical tests aimed at detecting temporal clustering within a given short series of diagnoses are presented. These tests are based on a standardized time interval between consecutive diagnoses. Two of the tests (the Cuscore and the Sets tests) are derived from sequential monitoring techniques which are sensitive to temporal clustering within the data set. The third test (R test) is not sequential and its sensitivity is focused on the average increase in the overall rate of the disease rather than on clustering within the series. Power curves are presented for conditions related to the intensity level of the subtle epidemic, the cluster size and the number of diagnoses. None of the techniques showed highest efficiency over all the specified conditions. The R test is the most efficient when the relative risk is 2 or less, and the Cuscore test is the most efficient method when the relative risk is > or = 2.5.

Decision Support Techniques↗

PubMed1998

Evaluation of night vision disturbances in contact lens wearers.

PURPOSE: We quantitatively recorded and evaluated night vision disturbances with physiologically dilated pupils. We compared the amount of image degradation experienced in eyes wearing spherical soft contact lenses with the amount of image degradation experienced by subjects wearing spectacles. METHODS: We prospectively evaluated 69 eyes from 35 myopic subjects with no ocular pathology. The subjects ranged in age from 22 to 35 years. We designed a test to quantitatively record image degradation with physiologically dilated pupils in scotopic conditions of dim ambient light. Previously, we have shown that this test accurately measures image degradation. We used this test to compare image degradation between new spherical soft contact lens and spectacle correction. Hyperopes and eyes with greater than 1.50 D of astigmatism were excluded. RESULTS: Adequately correcting myopic refractive error decreased recorded image degradation (P < or = 0.0001). There was no significant difference in the amount of image degradation between spectacle trial frames and new spherical soft contact lenses (P < or = 0.2885). CONCLUSIONS: Our test offers an objective method of assessing night vision disturbances in contact lens wearers. Our results suggest that image degradation, which may contribute to the sensation of glare experienced by some patients, is influenced equally by contact lens and spectacle correction.

Adult↗

PubMed1997

Dachshund and eyes absent proteins form a complex and function synergistically to induce ectopic eye development in Drosophila.

The eyeless, dachshund, and eyes absent genes encode conserved, nuclear proteins that are essential for eye development in Drosophila. Misexpression of eyeless or dachshund is also sufficient to induce the formation of ectopic compound eyes. Here we show that the dachshund and eyes absent genes act synergistically to induce ectopic retinal development and positively regulate the expression of each other. Moreover, we show that the Dachshund and Eyes Absent proteins can physically interact through conserved domains, suggesting a molecular basis for the genetic synergy observed and that a similar complex may function in mammals. We propose that a conserved regulatory network, rather than a linear hierarchy, controls retinal specification and involves multiple protein complexes that function during distinct steps of eye development.

Animals↗

PubMed1997

Structural constraints in protein engineering--the coenzyme specificity of Escherichia coli isocitrate dehydrogenase.

In a previous study we reported on the successful inversion of coenzyme specificity in isocitrate dehydrogenase (IDH) from NADP to NAD [Chen, R., Greer, A. & Dean, A. M. (1995) A highly active decarboxylating dehydrogenase with rationally inverted coenzyme specificity, Proc. Natl Acad. Sci. USA 92, 11666-11670]. Here, we explore alternative means to generate NAD dependence in the NADP-dependent scaffold of Escherichia coli IDH. The results reveal that engineering a preference for NAD is constrained by the architecture of the IDH coenzyme binding pocket and confirms that the substituted Asp344 in the engineered enzyme is the major determinant of coenzyme specificity. Mutations in the 316-325 loop, which forms part of the coenzyme binding site, reduce activity through transmission of long-range conformational changes into the active site some 14 A distant. Conformational changes seen upon substituting Cys332-->Tyr are not directly involved with improving activity. Replacements at Cys201 reveal that subtle changes in the packing of hydrophobic residues (Met and Ile versus Leu) can elicit markedly different responses. We caution against using sequence alignments as the sole guide for mutagenesis and show how a combination of rational design of active-site residues based on X-ray structures and random substitutions at surrounding residues provides an efficient means to improve enzyme preference and catalytic efficiency towards novel substrates.

Amino Acid Sequence↗

PubMed1997

The affected gene underlying the class K glycosylphosphatidylinositol (GPI) surface protein defect codes for the GPI transamidase.

The final step in glycosylphosphatidylinositol (GPI) anchoring of cell surface proteins consists of a transamidation reaction in which preassembled GPI donors are substituted for C-terminal signal sequences in nascent polypeptides. In previous studies we described a human K562 cell mutant, termed class K, that accumulates fully assembled GPI units but is unable to transfer them to N-terminally processed proproteins. In further work we showed that, unlike wild-type microsomes, microsomes from these cells are unable to support C-terminal interaction of proproteins with the small nucleophiles hydrazine or hydroxylamine, and that the cells thus are defective in transamidation. In this study, using a modified recombinant vaccinia transient transfection system in conjunction with a composite cDNA prepared by 5' extension of an existing GenBank sequence, we found that the genetic element affected in these cells corresponds to the human homolog of yGPI8, a gene affected in a yeast mutant strain exhibiting similar accumulation of GPI donors without transfer. hGPI8 gives rise to mRNAs of 1.6 and 1.9 kb, both encoding a protein of 395 amino acids that varies in cells with their ability to couple GPIs to proteins. The gene spans approximately 25 kb of DNA on chromosome 1. Reconstitution of class K cells with hGPI8 abolishes their accumulation of GPI precursors and restores C-terminal processing of GPI-anchored proteins. Also, hGPI8 restores the ability of microsomes from the mutant cells to yield an active carbonyl in the presence of a proprotein which is considered to be an intermediate in catalysis by a transamidase.

Acyltransferases↗

PubMed1997

Clustering of leukaemia cases in a city in Israel.

A temporal cluster of cases may result from exposure to a new carcinogen, but it may also occur under stable conditions or as result of another factor, such as changes in medical practice. In this study, we used several complementary methods to detect a cluster and to conduct an initial investigation regarding its cause. The analyses included three stages, and were based on the time interval between consecutive diagnoses. First, we applied the sets monitoring technique to detect clustering. Following the detection (alarm), a confirmatory analysis was conducted in order to confirm or refute it as a true alarm. We applied this analysis to the first five cases diagnosed subsequent to the alarm. With a graphical display of the temporal pattern of the diagnoses, we considered the possible causes leading to the cluster. The data included registered diagnoses of leukaemia cases made from 1960 to 1990 among residents of Ashkelon, Israel. Clustering was detected for acute lymphatic leukaemia and for chronic myeloid leukaemia. We found that the temporal patterns of the diagnoses consistent with the possibility that these two clusters are due to exposure to a common local carcinogen. We cannot however, rule out the possibility that these clusters are due to unknown factors.

Adolescent↗