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Biomedical subjects

V Chan

Publications and source records attributed to V Chan.

At least 73 records · Page 4Linked to original sources
PubMed1996

Molecular rearrangement of the MLL gene in adult acute myeloid leukemia without cytogenetic evidence of 11q23 aberration.

Translocations involving chromosome band 11q23 are frequently found in infant acute leukemia and involve rearrangement of the MLL gene. In this study, 29 cases of adult acute myeloid leukemia (AML) were analyzed to determine the frequency of MLL gene rearrangement. Of these, 19 cases were karyotyped and none showed cytogenetic evidence of 11q23 aberration. MLL rearrangements were demonstrable in four cases, giving a frequency of 14% (4/29). Only one of the four cases with MLL rearrangement showed features typical of leukemia with 11q23 aberration; other cases were indistinguishable from those without MLL rearrangement. There was no apparent difference in presentation blast count, remission, and survival duration when cases with or without MLL rearrangement were compared. Clinicopathologic features of adult AML with MLL rearrangements may be heterogeneous.

Adult↗
PubMed1996

Persistence of AML1 rearrangement in peripheral blood cells in t(8;21).

Translocation (8;21)(q22;q22) involves fusion of the AML1 gene with the ETO gene, generating an AML1/ETO fusion transcript that can be detected by the polymerase chain reaction (PCR). Persistence of the AML1/ETO transcript has been demonstrated by PCR in patients with t(8;21) in long-term remission, but the rearranged AML1 gene could not be detected by Southern analysis, showing that the t(8;21) clone existed as minimal residual disease (MRD). In one patient with t(8;21), AML1/ETO could be detected serially in the peripheral blood. However, rearrangement of the AML1 gene was also found to persist. Furthermore, the hybridization intensities of the rearrangement bands showed that some of the mature myeloid cells also possessed the AML1 rearrangement. Thus, the presence of AML1/ETO in this case appeared to be due to persistence of the mutated clone as mature myeloid cells instead of MRD, implying that the t(8;21) had occurred in a preleukemic myeloid progenitor cell capable of differentiation.

Acute Disease↗
PubMed1996

Molecular characterization of haemophilia A in southern Chinese.

41 unrelated southern Chinese haemophilia A patients were studied. The 5' promoter region, all 26 exons, their immediate 5' and 3' flanking splice junctions and the 3' untranslated region of the FVIII gene were amplified (including 16 different segments of exon 14) using GC-clamped primers. The GC-clamped PCR products were screened by denaturing gradient gel electrophoresis (DGGE) and fragments showing an abnormal migration pattern were sequenced. 17 mutations were identified, of which four were splicing defects, involving the first 1-6 nucleotide (nt) in the intervening sequences (IVS), six missense mutations, three nonsense mutations and four frameshift mutations. 14 other patients carried the type 1 inversion, affecting the distal copy of the FSA gene at the telomere of the X chromosome and the same gene in intron 22 of the FVIII gene. All the mothers studied (12/14) were carriers of the inversion. Two of these patients with inversion also have a co-existing missense mutation. In most cases the clinical severity of the disease corresponds to the genotype.

Base Sequence↗
PubMed1996

A semi-automated method for analysis of intron 13 and intron 22 dinucleotide repeat polymorphisms of the factor VIII gene.

A semi-automated method has been developed for the simultaneous analysis of two micro-satellite repeat polymorphisms located in intron 13 and 22 of the Factor VIII gene. The fluorescent dyes, 6-FAM-and HEX-phosphoramidites were used to 5'-end label the respective 5' primers of these two microsatellite repeats and a multiplex polymerase chain reaction (PCR) devised for amplification. The PCR product was loaded onto the gel with DNA size marker labelled with ROX. A total of 24 samples could be analysed simultaneously on an automated DNA sequencer. The results were computed using a dedicated software, with assignment of PCR product size in basepair. This method compares well with the conventional manual procedure using radio-labelled primers, but at the same time overcomes many of the inherent disadvantages associated with the latter method.

Alleles↗
PubMed1996

Case for active physician involvement in US practice.

PURPOSE: To assess the benefit of active physician involvement in ultrasound (US) examinations. MATERIALS AND METHODS: Concordance of findings by technologists and physicians was assessed prospectively for examinations of 1,510 consecutive patients who underwent US during regular working hours. RESULTS: Overall concordance was generally good (74%). However, in cases in which a major or minor new diagnosis was made from the US scan, concordance rates were substantially lower (36% and 32%, respectively). Agreement varied with the type of examination. The discordance rate for obstetric examinations (17%) was only half that for abdominal and pelvic examinations (31%). Concordance improved with increasing years of experience of the technologist. CONCLUSION: An active role of physicians in the overall conduct of US examinations is essential to optimize provision of a complete, accurate report.

Diagnostic Errors↗
PubMed1996

Model demonstrating respiratory mechanics for high school students.

We wanted to develop educational materials appropriate for the high school student which would present physiological concepts in an innovative way. The impetus was in response to the lack of physiology educational materials appropriate for the high school level. To this end, we developed an exercise that presents the physiological basis for respiratory mechanics. The materials were designed to engage students in interactive learning and to stimulate interest for future science study. The emphasis of the exercise was the construction of a model that could be built by high school students to demonstrate respiratory mechanics. The use of models to present complex materials has been shown to be an effective medium for science learning. Our exercise contains directions for an inexpensive, easy-to-build model, as well as many supplemental teaching tools. Questions are interspersed throughout the text and at the end of the laboratory experience to facilitate the learning process. Answers are provided to the questions. Students and teachers alike are challenged to build, manipulate, and discuss their experience during the investigation of respiratory mechanics.

Adolescent↗
PubMed1996

Construction of a model demonstrating neural pathways and reflex arcs.

Employment opportunities in the future will require higher skills and an understanding of mathematics and science. As a result of the growing number of careers that require solid science and mathematics training, the methods of science education are undergoing major reform. To adequately equip students for technologically advanced positions, new teaching methods must be developed that prepare tomorrow's workforce for the challenges of the 21st century. One such method is the use of models. By actively building and manipulating concrete models that represent scientific concepts, students are involved in the most basic level of Piaget's learning scheme: the sensorimotor stage. Models are useful in reaching all students at the foundational levels of learning, and further learning experiences are rapidly moved through higher learning levels. This success ensures greater comprehension and understanding compared with the traditional methods of rote memorization. We developed an exercise for the construction of an inexpensive, easy-to-build model demonstrating neural pathways and reflex arcs. Our exercise also includes many supplemental teaching tools. The exercise is designed to fulfill the need of sound physiological teaching materials for high school students.

Animals↗
PubMed1996

Antenatal and postnatal treatment of pleural effusion and extra-lobar pulmonary sequestration.

An infant is reported who was identified antenatally to have an extralobar sequestration and a pleural effusion. Chronic drainage of the effusion was achieved by placement of a pleuroamniotic shunt. After delivery the infant underwent several thoracocenteses and then definitive surgery to remove an extralobar sequestration. The postnatal course was documented by lung function measurements.

Adult↗
PubMed1995

Volume delivery during positive pressure inflation--relationship to spontaneous tidal volume of neonates.

Volume delivery by positive pressure inflation was determined in 20 premature infants and 10 infants born at term on days 1 and 2. The spontaneous tidal volume, respiratory rate and inspiratory to expiratory (I:E) ratio were measured daily in the first week of life in an additional group of 20 infants born prematurely. Measurements were made using a pneumotachograph only when the infants were stable and had acceptable blood gases for at least 2 h. There was variability between individuals but the median delivered volume by positive pressure ventilation ranged between 4.9 and 6.1 ml/kg on days 1 and 2 and within the groups of different maturity. There was no significant difference in the results of infants born prematurely or at term or when studied on days 1 or 2. The median spontaneous tidal volume during the first week of life varied between 5.4 and 6.7 ml/kg; respiratory rate between 72 and 80 breaths/min and I:E ratio from 0.67 to 0.77. Postnatal age had no significant effect on the results. These results suggest volume delivery by positive pressure inflation during a stable period of ventilation is similar to the spontaneous tidal volume.

Forced Expiratory Flow Rates↗
PubMed1995

Use of the polymerase chain reaction in the detection of AML1/ETO fusion transcript in t(8;21).

BACKGROUND: t(8;21)(q22;q22), found in acute myeloid leukemia (AML) and occasionally in myelodysplasia (MDS), results in the fusion of the AML1 gene on 22q22 to the ETO gene on 8q22, generating a chimeric AML1/ETO transcript, which is a molecular marker of the translocation. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR), with two pairs of nested AML1 and ETO primers, was used to amplify the AML1/ETO fusion transcript. The Kasumi-1 cell line was used as a positive control. RESULTS: RT-PCR has a sensitivity of 0.0001% (10(-6)), corresponding to detection of 0.5 picograms of leukemic RNA in the presence of 0.5 micrograms of normal RNA. Using this approach, patients with t(8;21) (three patients with de novo AML, one with therapy-related AML, and one patient with myelodysplasia) yielded the same 222 base pair PCR product, suggesting that the breakpoints occurred at the same AML1 and ETO introns as previously reported. Three patients were still PCR-positive when in complete remission after chemotherapy and two experienced relapse. However, in another three patients with t(8;21) who were in remission for 2 months, 2 years, and 3 1/2 years, respectively, PCR was negative. CONCLUSION: RT-PCR is a sensitive method of detection of t(8;21), and is useful in the monitoring of minimal residual leukemia. As the junction of AML1/ETO appears to be constant, RT-PCR may offer a quick and accurate diagnosis of t(8;21).

Adult↗
PubMed1995

High frequency oscillation, respiratory activity and changes in blood gases.

Spontaneous respiratory activity during high frequency oscillation (HFO) and its relationship to changes in blood gases on transfer to HFO has been assessed. Eighteen infants were studied, median gestational age 27 weeks and postnatal age 1 day. Simultaneous measurements of changes in oesophageal and airway pressure, flow and volume were made during a period of conventional ventilation and then during HFO. From these recordings, the infants' spontaneous respiratory rate during the two ventilatory techniques were calculated. Arterial blood gases were measured immediately before and after a 30-min period of HFO. All the infants were breathing during conventional ventilation (median rate of 55 breaths/min). On transfer to HFO, the respiratory rate of the whole group decreased to a median of 23 breaths/min (P < 0.001), but only five infants became apnoeic. The changes in respiratory rate did not relate significantly to changes in PaCO2. Oxygenation deteriorated in four of the five apnoeic infants and in the two infants who became agitated during HFO. In the remaining 11 infants, whose median respiratory rate was 28 breaths/min (range 15-77) during HFO, oxygenation improved by a median of 12 mmHg (range 4-42). We conclude that, in the majority of infants, spontaneous respiratory activity during HFO is compatible with improvements in blood gases.

Carbon Dioxide↗
PubMed1995

Simulium damnosum s.l.: identification of inducible serine proteases following an Onchocerca infection by differential display reverse transcription PCR.

Vector-derived proteases are thought to be key to the regulation of filarial infections in Simulium damnosum s.I. To identify proteases of S. damnosum s.I. induced by infection with Onchocerca ochengi, a PCR-based differential display technique was used. By combining this method with homology-based serine protease primers transcripts can be detected from S. damnosum s.I. RNA.

Amino Acid Sequence↗
PubMed1995

Prognostic indicators in congenital diaphragmatic hernia.

Congenital diaphragmatic hernia is associated with significant mortality and morbidity. The aim of this study was to compare a series of tests with respect to prediction of outcome. Tidal volume and compliance of the respiratory system (CRS) were measured preoperatively and on the first and second postoperative days. The maximum and modified ventilation indexes and the maximum Paco2 were noted for the first 6 hours of life and the first 6 hours postoperatively. In addition, it was recorded whether the stomach was within the ipsilateral hemithorax preoperatively. Twenty infants were studied (median gestational age, 38 weeks; range, 31 to 40), six of whom had a poor outcome, ie, they died or remained oxygen-dependent after 28 days. A CRS of less than 0.18 mL/cm H2O/kg was the most accurate predictor of poor outcome, with 66% sensitivity and 100% specificity. The authors conclude that lung function measurement are useful in the assessment of infants with congenital diaphragmatic hernia.

Carbon Dioxide↗
PubMed1995

The biophysics of DNA hybridization with immobilized oligonucleotide probes.

A mathematical model based on receptor-ligand interactions at a cell surface has been modified and further developed to represent heterogeneous DNA-DNA hybridization on a solid surface. The immobilized DNA molecules with known sequences are called probes, and the DNA molecules in solution with unknown sequences are called targets in this model. Capture of the perfectly complementary target is modeled as a combined reaction-diffusion limited irreversible reaction. In the model, there are two different mechanisms by which targets can hybridize with the complementary probes: direct hybridization from the solution and hybridization by molecules that adsorb nonspecifically and then surface diffuse to the probe. The results indicate that nonspecific adsorption of single-stranded DNA on the surface and subsequent two-dimensional diffusion can significantly enhance the overall reaction rate. Heterogeneous hybridization depends strongly on the rate constants for DNA adsorption/desorption in the non-probe-covered regions of the surface, the two-dimensional (2D) diffusion coefficient, and the size of probes and targets. The model shows that the overall kinetics of DNA hybridization to DNA on a solid support may be an extremely efficient process for physically realistic 2D diffusion coefficients, target concentrations, and surface probe densities. The implication for design and operation of a DNA hybridization surface is that there is an optimal surface probe density when 2D diffusion occurs; values above that optimum do not increase the capture rate. Our model predicts capture rates in agreement with those from recent experimental literature. The results of our analysis predict that several things can be done to improve heterogeneous hybridization: 1) the solution phase target molecules should be about 100 bases or less in size to speed solution-phase and surface diffusion; 2) conditions should be created such that reversible adsorption and two-dimensional diffusion occur in the surface regions between DNA probe molecules; 3) provided that 2) is satisfied, one can achieve results with a sparse probe coverage that are equal to or better than those obtained with a surface totally covered with DNA probes.

Base Composition↗
PubMed1995

Synchronous intermittent mandatory ventilation modes compared with patient triggered ventilation during weaning.

The efficacy of combining rate and pressure reduction during weaning by synchronous intermittent mandatory ventilation (SIMV) were compared with weaning by patient triggered ventilation (PTV) (pressure reduction alone) in two randomised trials. Regardless of ventilation mode, pressure was reduced to the same level according to the size of the infant. In the first trial, the SIMV rate was also reduced progressively to a minimum of 20 breaths/minute, and in the second to five breaths/minute. Forty premature infants aged 15 days of age or less were randomly allocated into each trial. No significant differences were found in the first trial between ventilation modes in either the duration of weaning or the number of infants in whom weaning failed. In the second trial, the duration of weaning was shorter by PTV than by SIMV (median 24 hours, range 7-432 v 50 hours, range 12-500; p < 0.05); weaning failed in two infants in the PTV group and in five in the SIMV group. It is concluded that weaning by a combination of pressure and rate reduction, such as can be achieved during SIMV, offers no significant advantage over pressure reduction alone.

Ductus Arteriosus, Patent↗