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Biomedical subjects

D F Tang-Wai

Publications and source records attributed to D F Tang-Wai.

9 recordsLinked to original sources
PubMed2005

Rate of progression differs in frontotemporal dementia and Alzheimer disease.

OBJECTIVE: To compare survival and rates of cognitive and functional decline in patients with autopsy-confirmed frontotemporal dementia (FTD) and Alzheimer disease (AD) in a large multicenter study. BACKGROUND: Despite advances in the clinical characterization of FTD, little is known about its rate of progression. Characterizing survival and rate of decline in FTD is important because it can provide prognostic guidelines and benchmarks to use in the evaluation of disease-modifying drugs. METHODS: Seventy patients with FTD and 70 patients with AD who were followed by seven Alzheimer disease research centers until confirmation of diagnosis at autopsy were matched for overall age, education, and Mini-Mental State Examination (MMSE) score at initial evaluation. Survival and rates of cognitive and functional decline were compared. RESULTS: Patients with FTD had significantly shorter survival from initial evaluation to death than patients with AD (FTD = 4.2 years, AD = 6.0 years; log-rank test = 5.17, p < 0.05), and they declined significantly faster over one year on the MMSE (mean annual rate of change: -6.7 points for FTD vs -2.3 points for AD). A significantly greater proportion of patients with FTD were impaired in basic activities of daily living (ADLs) at initial evaluation, and lost the capacity for independent or minimally-assisted ADLs over the subsequent year. CONCLUSIONS: The results are consistent with shorter survival and faster rates of cognitive and functional decline in patients with frontotemporal dementia (FTD) compared to those with Alzheimer disease (AD). This suggests that FTD follows a more malignant disease course than AD once dementia is clinically recognized.

Activities of Daily Living↗
PubMed2004

1H MR spectroscopy in common dementias.

OBJECTIVE: To determine the 1H MR spectroscopic (MRS) findings and intergroup differences among common dementias: Alzheimer disease (AD), vascular dementia (VaD), dementia with Lewy bodies (DLB), and frontotemporal lobar degeneration (FTLD). METHODS: The authors consecutively recruited 206 normal elderly subjects and 121 patients with AD, 41 with FTLD, 20 with DLB, and 8 with VaD. The 1H MRS metabolite ratio changes in common dementias were evaluated with respect to normal and also differences among the common dementias. RESULTS: N-acetylaspartate (NAA)/creatine (Cr) was lower than normal in patients with AD, FTLD, and VaD. Myo-inositol (mI)/Cr was higher than normal in patients with AD and FTLD. Choline (Cho)/Cr was higher than normal in patients with AD, FTLD, and DLB. There were no metabolite differences between patients with AD and FTLD or between patients with DLB and VaD. NAA/Cr was lower in patients with AD and FTLD than DLB. MI/Cr was higher in patients with AD and FTLD than VaD. MI/Cr was also higher in patients with FTLD than DLB. CONCLUSIONS: NAA/Cr levels are decreased in dementias that are characterized by neuron loss, such as AD, FTLD, and VaD. MI/Cr levels are elevated in dementias that are pathologically characterized by gliosis, such as AD and FTLD. Cho/Cr levels are elevated in dementias that are characterized by a profound cholinergic deficit, such as AD and DLB.

Acetylcholine↗
PubMed2004

Clinical, genetic, and neuropathologic characteristics of posterior cortical atrophy.

OBJECTIVE: To examine the clinical, genetic, and neuropathologic features of posterior cortical atrophy (PCA). DESIGN/METHODS: Using a broad definition of PCA as a syndrome with the insidious onset of visual dysfunction in the absence of primary ophthalmologic causes, the authors identified and then reviewed the presenting signs and symptoms, ApoE genotypes, tau haplotypes, and neuropathologic findings when available of PCA cases from two dementia research centers collected over the past 14 years. RESULTS: The authors identified 40 PCA cases. Their mean age at symptom onset was 60.5 +/- 8.9 years. There were twice as many women as men in the series. The principal types of visual impairment were simultanagnosia (82%) and visual field defect (47.5%). Acalculia, alexia, and anomia were also common. Insight was preserved in almost all (95%) early in the disorder. Neither apoE epsilon4 nor tau haplotype frequencies were different from typical Alzheimer disease (AD). Nine patients had died and underwent postmortem examination. Seven autopsied cases had AD pathology but when compared to typical AD, the neurofibrillary tangle (NFT) densities were significantly higher in Brodmann areas 17 and 18 (p < 0.05) and significantly lower in the hippocampus (p < 0.05). Two cases had corticobasal degeneration with maximal involvement of tau positive glial pathology in the posterior parietal lobe and Brodmann areas 17 and 18. CONCLUSIONS: PCA is a distinctive dementia syndrome in which the most pronounced pathologic involvement is in the occipitoparietal regions independent of the specific underlying pathology. AD was the most common pathologic cause, but its regional distribution differed from typical AD.

Adult↗
PubMed2003

Pathologically confirmed corticobasal degeneration presenting with visuospatial dysfunction.

Corticobasal degeneration (CBD) typically manifests as progressive asymmetric rigidity and apraxia, although other non-motor presentations have been reported. We report two patients with pathologically diagnosed CBD who presented with prominent visuospatial dysfunction. The pathological changes were maximal in the visual association cortices, but absent in 31 cases of pathologically proven CBD with more typical antemortem features. Underlying CBD should be considered in the differential diagnosis of patients with findings reflecting posterior cerebral dysfunction.

Aged↗
PubMed2003

Comparison of memory fMRI response among normal, MCI, and Alzheimer's patients.

OBJECTIVE: To determine whether an fMRI memory encoding task distinguishes among cognitively normal elderly individuals, patients with mild cognitive impairment (MCI), and patients with early Alzheimer's disease (AD). METHODS: Twenty-nine subjects (11 normal, 9 MCI, 9 AD) were studied with an fMRI memory encoding task. A passive sensory task was also performed to assess potential intergroup differences in fMRI responsiveness. Activation in the medial temporal lobe for the memory task and in the anatomic rolandic area for the sensory task was studied. Intergroup comparisons were performed using receiver operating characteristic (ROC) analyses. The ROC method provides rigorous control of artifactual false-positive "activation." Subjects were tested for recall and recognition of the encoding task stimuli following the fMRI study. RESULTS: Medial temporal lobe activation was greater in normal subjects than MCI and AD patients (p = 0.03 and p = 0.04). There was no difference between AD and MCI patients in fMRI memory performance [corrected]. There was an association between fMRI memory activation (area under the ROC curve) and post-fMRI performance on recognition and free recall. There was no difference among the three groups on the sensory task. CONCLUSIONS: MCI and AD patients had less medial temporal lobe activation on the memory task than the normal subjects but similar activation as normal subjects on the sensory task. These findings suggest decreased medial temporal activation may be a specific marker of limbic dysfunction due to the neurodegenerative changes of AD. In addition, fMRI is sufficiently sensitive to detect changes in the prodromal, MCI, phase of the disease.

Aged↗
PubMed2001

Hypertensive encephalopathy presenting with thunderclap headache.

A 68-year-old woman presented with thunderclap headache, which led to a search for subarachnoid hemorrhage. Both computerized tomography of the head and cerebrospinal fluid examination were normal. Magnetic resonance imaging revealed abnormalities in the white matter in the parieto-occipital regions. There was no aneurysm on magnetic resonance angiography. Treatment of hypertension led to resolution of the posterior leukoencephalopathy. Hypertensive encephalopathy with reversible posterior leukoencephalopathy can present as a thunderclap headache.

Acute Disease↗
PubMed1995

Human (MDR1) and mouse (mdr1, mdr3) P-glycoproteins can be distinguished by their respective drug resistance profiles and sensitivity to modulators.

Possible functional differences between P-glycoproteins (P-gps) encoded by the human MDR1 and mouse mdr1 and mdr3 genes with respect to drug resistance profiles and sensitivity to known modulators have been investigated. For this, the three genes were introduced and overexpressed in the same cellular background, that of Chinese hamster LR73 ovary cells, and drug-resistant clones expressing comparable amounts of the corresponding P-gps were selected under the same conditions. Analysis of the specific drug resistance profiles encoded by each P-gp for colchicine, adriamycin, vinblastine, and actinomycin D revealed overlapping but distinct patterns of drug resistance for the three isoforms. While all three P-gps conferred levels of resistance to vinblastine that did not vary by more than 2.5-fold, each isoform could be clearly distinguished by its capacity to confer resistance to colchicine and actinomycin D. Likewise, the study of structurally related and unrelated P-gp modulators indicated strong isoform-specific differences in the capacity of individual modulators to abrogate vinblastine resistance in the corresponding mdr transfectants. The study of several disubstituted piperazine analogs indicated that minor chemical modifications of the linker region of this modulator had strong effects on the sensitivity profile of each isoform to the modulator. Together, these results indicate that the three P-gp isoforms analyzed have specific and distinguishable functional characteristics with respect to interactions with drugs and modulators. These findings also suggest that P-gp positive murine transplantable tumors should be used with caution in the design and in vivo testing of novel P-gp modulators to be used to reverse multidrug resistance to tumor cells expressing human MDR1.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

The nitrogen of the acetamido group of colchicine modulates P-glycoprotein-mediated multidrug resistance.

The substituents of drug molecules and the specific amino acid residues of P-glycoprotein (P-gp) implicated in drug/protein interactions are largely unknown. We have used a series of colchicine analogs modified on the A, B, and C rings to identify the discrete chemical groups on the colchicine molecule that are required for recognition by P-gp. For this, the toxicity of these analogs was tested on independent cell clones expressing either of the two mouse mdr genes, mdr1 and mdr3, known to confer multidrug resistance. Modifications of the methoxy groups on the A and C rings modulated cellular toxicity but had no effect on P-gp recognition; however, modifications at the C7 position of the B ring, in particular the removal of the nitrogen atom of the acetamido group, had a dramatic effect. Analogs bearing a hydrogen at that position were not substrates for P-gp. The importance of the nitrogen at C7 was independently verified in thiocolchicine and allocolchicine analogs similarly modified, although overall levels of resistance to these compounds were somewhat reduced compared to their colchicine counterparts. The study of allocolchicine congeners bearing a six-carbon C ring and of two other analogs completely lacking a B ring suggested that intact B and C rings were important for interaction with P-gp. These results suggest that the structural determinants for cytotoxicity (tubulin binding) and P-gp recognition map to nonoverlapping sites in the colchicine analogs analyzed. Examination of calculated molar refractivities (CMR) revealed that only compounds showing CMR values greater than 9.7 were P-gp substrates.(ABSTRACT TRUNCATED AT 250 WORDS)

ATP Binding Cassette Transporter, Subfamily B, Mem↗