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Biomedical subjects

V Chan

Publications and source records attributed to V Chan.

At least 91 records · Page 5Linked to original sources
PubMed1995

DNA analysis of Huntington's disease in southern Chinese.

Allelic frequencies of RFLPs at loci closely linked to the HD gene, D4S95, D4S91, D4S141, and D4S90, were determined in 13 Huntington's disease (HD) patients from nine Chinese families and 129 normal subjects. These were similar for non-HD and HD chromosomes and the HD gene in Chinese is associated with multiple haplotypes. Hence the HD gene probably arose independently in the background haplotypes of the Chinese population. The heterozygosity rates for the two most useful RFLP sites are 0.659 for D4S95-AccI VNTR and 0.494 for D4S141-HindIII. (CAG)n repeat numbers ranged from 12 to 27 in 174 normal chromosomes. In 52 meiotic recombinations, the (CAG)n repeats were stably inherited in normal families. In HD families, 12 of 13 HD patients had expanded (CAG)n repeats of 40 to 58. Additionally, 10 asymptomatic family members had expanded (CAG)n repeats and the inheritance of the expanded repeat was unstable in these families.

Alleles↗
PubMed1995

Screening for urothelial malignancies by cytologic analysis and flow cytometry in a community urologic practice: a prospective study.

A prospective study was initiated to compare the ability of flow cytometry and cytologic analysis to detect malignant cells in urine obtained at the time of cystoscopy. The population studied consisted of patients from general urologic practices who were undergoing cystoscopy in a single community hospital. Over a 1-yr period, 335 specimens from 317 patients were studied. Nineteen biopsy-proven urothelial malignancies were identified. Cytologic examination of urine obtained at the time of cystoscopy was positive in seven of these cases, and an aneuploid population of cells was identified by flow cytometry in three cases. All three cases of high-grade transitional cell carcinoma and carcinoma in situ were correctly identified by the combination of cytologic examination and flow cytometry; however, only four of 16 low-grade superficial papillary transitional cell carcinomas were recognized cytologically, with only one being aneuploid. The combination of cytologic analysis and flow cytometry did not increase the diagnostic sensitivity above that achieved with cytologic testing alone (overall sensitivity, 37%). We conclude that flow cytometry and cytologic analysis, either individually or in combination, are too insensitive for use in a routine screening program for urothelial malignancy in a community hospital setting because of the inability of either method to detect low-grade transitional cell carcinomas reliably.

Carcinoma, Squamous Cell↗
PubMed1995

Mixed chimerism following bone marrow transplantation for severe combined immunodeficiency: a study by DNA fingerprinting and simultaneous immunophenotyping and fluorescence in situ hybridisation.

We report a girl with severe combined immunodeficiency (SCID) who had a paternal T-depleted bone marrow transplant (BMT) when 11 months old. Engraftment was documented but karyotyping of marrow cells 1 year after BMT showed recipient metaphases (XX) only. However, she remained clinically well and further analysis y karyotyping of PHA-cultured peripheral blood mononuclear cells (PBMC) showed donor metaphases (XY) only. DNA fingerprinting confirmed mixed chimerism in the peripheral blood. The granulocytes were of recipient origin and the PBMC of mixed origin, the donor proportion of which increased after culture with PHA. Using simultaneous immunophenotyping and fluorescence in situ hybridisation (FISH) with chromosomes X and Y-specific probes, circulating T cells were demonstrated to be of donor origin whereas B cells and myeloid cells were mostly of recipient origin.

Adult↗
PubMed1994

Ultrasound measurement of placental thickness to detect pregnancies affected by homozygous alpha-thalassaemia-1.

Homozygous alpha-thalassaemia-1, a common cause of hydrops fetalis, is usually diagnosed invasively. We measured placental thickness by ultrasound at 10-21 weeks' gestation in 231 at-risk pregnancies. 60 were affected (by DNA analysis). The sensitivity and specificity in detecting affected pregnancies at cut-off of mean placental thickness plus 2 SD before 12 weeks' gestation were 0.72 (95% CI 0.52-0.93) and 0.97 (0.9-1.0). After 12 weeks sensitivity increased to 0.95 (0.89-1.0) and by 18 weeks reached 1.0 (0.60-0.99) without change in specificity. Selection of pregnancies at risk by measurement of placental thickness will reduce the number of invasive diagnostic procedures.

Female↗
PubMed1994

Influence of lung function and reflex activity on the success of patient-triggered ventilation.

The influence of lung function and reflex activity on the success of patient-triggered ventilation (PTV) has been determined. Lung function was assessed by measurement of compliance using a single breath technique. Reflex activity was assessed by measurement of the strength of Hering Breuer reflex indicated by the degree of prolongation of expiration following end inspiratory occlusion. PTV was considered to have failed if the infant became apnoeic or required an increased level of respiratory support. Twenty premature infants (median gestational age 29 weeks) in the recovery stage of respiratory distress, were studied at a median postnatal age of 2.5 days. PTV failed ultimately in six infants, although compliance of the respiratory system of that group did not differ significantly from the rest of the cohort, their Hering Breuer reflex was significantly weaker (P < 0.01). In addition, the infants in whom PTV failed were significantly more immature and of lower birthweight (P < 0.01) compared with those in whom it succeeded. We conclude that failure of PTV is more likely in immature infants who have a weak Hering Breuer reflex.

Humans↗
PubMed1994

Disease severity and optimum mean airway pressure level on transfer to high frequency oscillation.

The aim of this study was to assess whether the severity of the infant's lung disease determined the most appropriate change in mean airway pressure (MAP) level to use on transfer from conventional ventilation to high frequency oscillation (HFO). In addition, we wished to assess whether the oscillatory frequency employed affected gas exchange. Ten premature infants with respiratory distress syndrome (RDS) were studied at a mean postnatal age of 1.5 days. During HFO, the infants were studied at a MAP equivalent of that used during conventional ventilation (baseline MAP), then at 2 and 5 cmH2O above baseline at 10 Hz. At the MAP identified as optimum, that is, the one associated with the best oxygenation, the infants were then studied at 10, 15 and 20 Hz. Each oscillatory setting was maintained for 20 minutes after which time arterial blood gases were measured. Prior to transfer to the oscillator, the peak inspiratory pressure was recorded, the P(A-a)O2 calculated and compliance of the respiratory system (Crs) measured. In nine infants, the optimum baseline MAP was +5 cmH2O. Oxygenation at that level was better than on conventional ventilation (P < 0.05), but there was no significant change in CO2 elimination. The optimum MAP was related to the peak pressure during conventional ventilation (P < 0.01) and inversely related to Crs (P < 0.01). There was no significant relationship with the P(A-a)O2. At the optimum MAP, the only significant effect of frequency was an impairment of oxygenation at 20 Hz.(ABSTRACT TRUNCATED AT 250 WORDS)

High-Frequency Ventilation↗
PubMed1994

A novel haemophilia B defect due to partial duplication of the factor IX gene.

A patient with mild FIX deficiency was found to have partial duplication of the 3' region of the gene, giving, in addition to the a normal gene, another piece of DNA containing exons 5', 6', 7' and 8' and the intervening sequences. Cloning and sequencing of the junction region revealed that crossover occurred at nt 31927 in the 3' untranslated region of one chromosome/chromatid and nt 10640 in intron 4 of the other. No homology or topoisomerase specific sequences were observed in the crossover region. PCR and sequencing of illegitimate FIX transcripts from the patient's lymphocytes showed at least three different species of mRNAs. Translation of two of these 'novel' mRNAs should result in truncated proteins. Possibilities for the splicing of the mature mRNA are offered to explain the translation of a normal-size FIX protein, which was the only product demonstrated on Western blot analysis.

Base Sequence↗
PubMed1994

Intragenic dinucleotide repeats in factor VIII gene for the diagnosis of haemophilia A.

Two multi-allelic microsatellite polymorphisms within the factor VIII gene were studied in 138 Chinese subjects. The allele sizes detected were higher than those found in Caucasian populations, whereas the heterozygosity rates were lower, being 0.5370 for intron 13 and 0.4444 for intron 22 repeats respectively. Their usefulness in diagnosis was compared to other intragenic and extragenic RFLPs, using previous data on the same 31 unrelated haemophilia A families. These intragenic microsatellite repeat polymorphisms were only informative for 18/31 families (58%); however, with the combined use of all existing RFLPs, the cumulative informativeness would be 100%.

Asian People↗
PubMed1994

Pituitary stone: two cases of densely calcified thyrotrophin-secreting pituitary adenomas.

Calcification is a well recognized but relatively uncommon feature of prolactin-secreting, growth hormone-secreting and non-functional pituitary tumours. It varies in extent, but rarely exceeds a tiny amount histologically or radiologically. Thyrotroph adenomas are the rarest of the secretory pituitary tumours, accounting for less than 1% of cases, and partial calcification of such lesions has been reported in only three cases. We describe two patients in whom the clinical and biochemical features indicated the presence of a TSH-secreting adenoma and radiology demonstrated a large 'pituitary stone'. One patient, a 59-year-old female, initially presented with hyperthyroidism, aged 18, and was rendered euthyroid by two subtotal thyroidectomies before a pituitary lesion was suspected, over 20 years later. Autonomous secretion of thyrotrophin was demonstrated by dynamic tests, and the failure of exogenous T3 to reduce the serum TSH. In the absence of tumour expansion and compressive symptoms, pituitary surgery was not undertaken. At the age of 56, she developed symptoms of intermittent ataxia and diplopia, culminating in a focal seizure, and was found on CT scan to have, in addition to the pituitary lesion, a parasagittal meningioma. This was successfully removed at craniotomy. In the second patient, a 42-year-old male, the finding of hyperthyroidism in association with an elevated TSH concentration led to the discovery of a pituitary stone which was removed transethmoidally, together with surrounding adenomatous tissue which stained positively for TSH on immunocytochemistry.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗
PubMed1994

Psychosocial impact of Huntington's disease on Hong Kong Chinese families.

Twenty-eight asymptomatic relatives from 7 Chinese families with Huntington's disease (HD) received psychosocial assessment. One third of these subjects (n = 9) had symptoms of anxiety and depression that warranted a Present State Examination (PSE) diagnosis. One quarter of these subjects (n = 8) would contemplate suicide if their predictive testing indicated a high risk of having the disease. This suicidal risk was associated with a PSE diagnosis of depression and a stress-coping repertoire with a high proportion of coping strategies of the avoidance type at the time of interview. Early and close liaison with these subjects for the detection of mental symptoms and provision of counselling on a balanced and positive coping style is essential.

Adaptation, Psychological↗
PubMed1994

Inspiratory and expiratory times for infants ventilator-dependent beyond the first week.

The aim of this study was to determine optimum inspiratory and expiratory times to be used for ventilation of infants older than one week of age. Each infant was studied at a rate of 30 breaths/min (inspiratory times (TI) of 1.0, 0.67 and 0.5 s with expiratory times (TE) of 1.0, 1.33 and 1.5 s, respectively) and at a rate of 60 breaths/min (TI 0.5, 0.33 and 0.25 s and TE 0.5, 0.67 and 0.75 s, respectively). Arterial blood-gases were examined after 20 min on each setting. Fifteen infants with a median gestational age of 27 weeks were studied at a median postnatal age of 9 days and 10 infants with a median gestational age of 27 weeks at a median postnatal age of 24 days. All infants had type I chronic lung disease. Oxygenation did not consistently improve as TI was prolonged, elevating mean airway pressure but, particularly in older infants, was better at TI > or = 0.5 s compared with TI < 0.5 s. In both groups, carbon dioxide elimination was better at 60 than at 30 breaths/min. Thus we suggest that in infants fully ventilator-dependent beyond the first week of life, an inspiratory and expiratory time of 0.5 s should be used as the first choice.

Humans↗
PubMed1994

Comparison of weaning by patient triggered ventilation or synchronous intermittent mandatory ventilation in preterm infants.

Forty preterm infants were entered into a randomized controlled trial to compare the efficacy and duration of weaning by patient triggered ventilation (PTV) to that of synchronous intermittent mandatory ventilation (SIMV). Infants were randomized during recovery from respiratory distress once ventilator rate had been reduced to 40 breaths per minute; weaning during PTV was by reduction in ventilator pressure only, whereas infants randomized to SIMV were weaned by reduction in rate only. Weaning failed in 12 infants, 6 from each group, the 12 infants were more immature than those in whom weaning succeeded (p < 0.01). Overall, the duration of weaning did not differ significantly between the PTV and SIMV groups.

Gestational Age↗
PubMed1994

High frequency oscillation for preterm infants with severe respiratory failure.

High frequency oscillation (HFO) as rescue treatment for preterm infants with severe respiratory failure has been assessed and prognostic factors identified. Thirty six infants with a median gestational age of 27 weeks were studied. Immediately before transfer to HFO, the infants were receiving an inspired oxygen concentration of > or = 85% and/or a mean airway pressure of > or = 12 cm H2O and had a median alveolar-arterial oxygen gradient (A-aDO2) of 73.28 kPa (range 49.34-89.91). Seventeen infants subsequently died. Comparison of those 17 with the remaining 19 infants demonstrated that respiratory distress syndrome and persistent fetal circulation were associated with a significantly better outcome than pulmonary airleak. The A-aDO2 after two and six hours on HFO was significantly higher in those infants who survived compared with those who died. We conclude that a diagnosis of pulmonary airleak and failure to show early improvement in respiratory status indicate a poor prognosis when HFO is used as rescue treatment.

Air Pressure↗
PubMed1994

The effect of frequency on carbon dioxide levels during high frequency oscillation.

The aim of this study was to assess if, during high frequency oscillation (HFO), a frequency of 10 or 15 Hz was associated with lower carbon dioxide levels. Twelve infants were recruited, median gestational age 27 weeks. All infants were studied at both frequencies, applied in random order and the carbon dioxide level checked after 30 minutes on each frequency. Carbon dioxide levels were lower in 10 of the 12 infants at 10 compared to 15 Hz (p < 0.004) and, in the study population, overall were significantly lower at 10 Hz (p < 0.05). The difference in paCO2 levels at the two frequencies, however, was small, thus these results suggest the clinician should rely primarily on changes in oscillatory amplitude, rather than frequency, to effect changes in carbon dioxide levels.

Bronchopulmonary Dysplasia↗
PubMed1994

The performance of a new valveless ventilator at rates of up to 250 bpm.

The efficacy of a new ventilator, incorporating a valveless pneumatic exhalation circuit, at rates of up to 250 bpm was first assessed in the laboratory. Using this ventilator the effect of fast rate ventilation on blood gases of infants with acute respiratory distress was then examined. Infants were studied at three rates: 60, 125 and 250 bpm. Peak inflating and positive end expiratory pressure, inspiratory: expiratory ratio and inspired oxygen were kept constant. The laboratory study demonstrated that as ventilator rate was increased the delivered volume fell, but even at 250 bpm the delivered volume was 7 ml. In the clinical study, oxygenation at 250 bpm was not significantly different from that at 60 bpm, but significantly lower than at 125 pbm. Carbon dioxide levels were significantly lower at 250 bpm that at 60 bpm, but did not differ significantly from that at 125 bpm. We conclude increasing ventilator rate from 125 to 250 bpm is not advantageous for infants ventilated for acute respiratory distress.

Case-Control Studies↗
PubMed1994

Huntington's disease in Hong Kong Chinese: epidemiology and clinical picture.

In a territory-wide survey of Huntington's disease (HD) in the Chinese population of Hong Kong, 20 patients from 11 families were identified from 1984 to 1991, giving a low period prevalence of 3.7 per 10(6) population. Six patients had died by 1991, hence the point prevalence was even lower, being 2.5 per 10(6) population. The male to female ratio was 3:1. No paternal transmission effect on the age of onset was observed. Apart from these differences, the clinical and pathological features were similar to those seen in the West.

Adult↗