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T K Chan

Publications and source records attributed to T K Chan.

At least 19 recordsLinked to original sources
PubMed2006

Experience in preimplantation genetic diagnosis for exclusion of homozygous alpha degrees thalassemia.

OBJECTIVE: To report our experience in preimplantation genetic diagnosis (PGD) for the exclusion of homozygous alpha degrees thalassemia. PATIENTS AND METHODS: PGD was performed on nine couples with alpha degrees thalassemia genotype undergoing assisted reproduction. Oocytes were aspirated after ovarian stimulation and fertilized by intracytoplasmic sperm injection. One or two blastomeres were biopsied from the six- to eight-cell embryo. Single cell multiplex PCR of the normal and alpha degrees thalassemia alleles was performed for first round, followed by semi-nested PCR of the respective alleles using 5'-end labelled fluorescent primers. Only those embryos with a blastomere diagnosed as having at least one normal allele were selected for transfer. RESULTS: One hundred and twenty-six blastomeres from 82 embryos were analyzed. The rates of allele dropout was 10.2% and PCR failure 12.7%. Fifty-eight embryos (70.7%) had at least one normal allele, of which 31 were transferred to 13 prepared cycles and one triplet pregnancy achieved. The triplets showed no ultrasound features of homozygous alpha degrees thalassemia at 18 weeks and were delivered in healthy condition by caesarean section at 34 weeks. Their genotypes were confirmed by cord blood analysis. CONCLUSIONS: PGD for alpha degrees thalassemia is possible by single cell PCR. The transfer and successful implantation of unaffected embryos ensure birth of disease-free babies.

Alleles↗
PubMed2006

Functional outcome of the hand following flexor tendon repair at the 'no man's land'.

PURPOSE: To evaluate the functional outcome of the hand following flexor tendon repair at 'no man's land' using 2 strands of a modified Kessler core suture and combined controlled motion rehabilitation protocol. METHODS: Records of 31 zone-2 flexor tendon injuries in 21 digits of 16 patients between July 2000 and June 2005 were reviewed retrospectively. The injured tendons were repaired within 24 hours using 2 strands of a modified Kessler core suture, reinforced by a continuous circumferential epitendon suture. All patients completed a rehabilitation protocol that included active extension against a rubber band, passive flexion, and controlled passive extension and passive flexion exercises. Functional outcome of the fingers was assessed using the Buck-Gramcko II score. Hand grip strength, rehabilitation period, and rupture rate were also measured. RESULTS: 17 (81%) out of 21 digits in 15 out of 16 patients achieved an excellent-to-good functional grade. The remaining patient with concomitant injuries to 4 (19%) digits attained a poor functional grade, attributable to poor compliance with the rehabilitation protocol. The mean rehabilitation period was 130 days and the mean grip strength was 78% that of the uninjured side. Concomitant digital nerve injury did not adversely affect the final outcome. Only one (4.8%) patient experienced a rupture. CONCLUSION: The surgical method and rehabilitation protocol used for zone-2 flexor tendon injury is safe and results in a reasonably good functional outcome.

Adolescent↗
PubMed2004

A thalassaemia array for Southeast Asia.

The alpha and beta thalassaemias are the commonest genetic disorders worldwide. The homozygous state is associated with high morbidity and mortality, thus screening of at-risk pregnancies and prenatal testing are strongly advocated. A thalassaemia (thal) array has been designed using allele-specific arrayed primer extension (AS-APEX) for the simultaneous analysis of 15 non-deletion alpha-gene defects and 23 beta-gene mutations commonly found in southeast Asian countries, where thalassaemias are highly prevalent. This overcomes the problem of using multiple reverse dot blot analysis. The array showed 100% sensitivity and specificity in the detection of 120 beta-thal mutants and 35 non-deletion alpha-thal mutants. It is robust enough to be produced in a single place and shipped to other laboratories for use. The production cost of the array is low, each slide can be used for three different test samples and is therefore amenable to large scale antenatal screening in southeast Asian countries.

Asia, Southeastern↗
PubMed2003

Long-term survival of primary root canal treatment carried out in a dental teaching hospital.

AIM: This study aimed to examine clinically and radiographically the survival of primary root canal treatment completed in a dental teaching hospital between 10 and 20 years previously. METHODOLOGY: A data collection form was used to collate all information obtained from the written patients' records along with the results from clinical and radiographic examination of 608 teeth, out of a total of 986 randomly selected teeth that had been root filled in the Prince Philip Dental Hospital (PPDH), Hong Kong, between 1981 and 1989. The criteria for failure were extractions (except for documented nonendodontic reason), retreatments and presence of a periapical radiolucency. The survival function of the treated teeth was plotted against the calculated date of failure using the Kaplan-Meier (K-M) method. Covariables were examined further by Cox Regression analysis with a backward stepwise method. RESULTS: A total of 314 teeth (52%) were either documented or deemed to have failed after examination. The median survival time was 111 months. Cox Regression analysis indicated that the survival of root-filled teeth was significantly influenced by the tooth type, preoperative periapical status and the type of coronal restoration. The survival function declined with time, with a rapid drop in the first 18 months or so. The rate at which failures occurred appeared to slow down with a longer observation time. CONCLUSIONS: There was a nonlinear decline in the cumulative survival probability of primary root canal treatment. Tooth type, preoperative periapical status and type of post and final restoration significantly affected the long-term survival of the treated teeth.

Crowns↗
PubMed2001

Effect of storage conditions on calcium sulphate hemihydrate-containing products.

OBJECTIVE: Dental gypsum products are liable to deterioration on exposure to the air because of reaction between calcium sulphate hemihydrate and water vapour. The purpose of this investigation was to refine the knowledge of the conditions and rates at which this occurred for a representative selection of such products with a view to improved storage recommendations. MATERIALS AND METHODS: Absorption of water from controlled atmospheres (25-40 degrees C, 75-99% RH) was monitored gravimetrically for a dental artificial Stone, Plaster of Paris, an Impression plaster and a gypsum-bonded Investment. RESULTS: An initial steady absorption stage was followed by a transition to a rapid absorption; this led to a completion stage as the presumed hydration reaction approached completion. The logarithm of time of the transition showed approximately linear dependence on the relative humidity (and not on water vapour pressure as might have been expected) and a slight but significant (P<0.005) negative dependence on temperature in the range 25-35 degrees C for Stone, Plaster of Paris and the Impression plaster, but not for the Investment (P>0.5). The behaviour for the first three materials at 40 degrees C departed significantly from the temperature-dependent trend (P<0.05) while the Investment showed no such effect. The absorption by the Investment was substantially faster than for the other materials. SIGNIFICANCE: There is no evidence to suggest that there is a 'safe' humidity for exposure to the atmosphere although for the Stone and Plasters at RH <70% in excess of 1000 h is predicted to be necessary before rapid reaction commences. For the Investment, the equivalent time at 70% RH is 1d.

Absorption↗
PubMed2001

Autosomal dominant congenital superior oblique palsy.

PURPOSE: We describe a mother and all her offspring with congenital superior oblique palsy (CSOP), and a father and all his sons with unilateral CSOP. We discuss the inheritance pattern in our pedigrees and compare it with previous reports. METHOD: All available family members were examined. The prism cover test was performed. Ocular movements were examined in all positions of gaze and where possible a Hess chart plotted. Lang and TNO stereotests were used to determine the stereo-acuity. The results of these tests combined with the Bielschowsky head tilt test (BHTT) were used to confirm the diagnosis of superior oblique palsy. The condition was classified as congenital if it presented early based on history or the observation of old photographs and in the absence of a causative factor. RESULTS: The affected members of family A consist of a father and his three sons with unilateral CSOP. His daughter had a mild weakness of her left inferior and superior rectus muscle. One of his sons was asymptomatic and only recognised on screening of the family for the study. The affected members of family B consist of a mother and her younger daughter with unilateral CSOP and her older daughter with bilateral CSOP. She had no other children. CONCLUSIONS: Our families demonstrate what is probably an autosomal dominant form of CSOP. It is possible that hereditary CSOP is more common than previously reported.

Adult↗
PubMed2001

Quantitative polymerase chain reaction for the rapid prenatal diagnosis of homozygous alpha-thalassaemia (Hb Barts hydrops fetalis).

A quantitative polymerase chain reaction (Q-PCR) method based on the TaqMan technology has been devised for the prenatal diagnosis of homozygous alpha*-thalassaemia (south-east Asian type deletion). Primers and TaqMan probes were designed to specifically amplify an alpha*-thal chromosomal fragment or a normal alpha-chromosomal fragment. Variations in input target DNA in individual sample wells were normalized by the simultaneous amplification of a beta-actin gene fragment and results expressed as a ratio to that of beta-actin. There was no overlap of the data between the homozygous alpha*-thal, alpha*-thal and normal subjects. Up to 5% maternal DNA (alpha*-thal) contamination did not affect the specificity of the result. In 31 prenatal diagnoses, the result using Q-PCR compared favourably with the gold standard of Southern hybridization of alpha-genes.

Actins↗
PubMed2001

Timing of postoperative adjustment in adjustable suture strabismus surgery.

PURPOSE: The use of adjustable sutures in strabismus surgery has increased the rate of surgical success. Little data are available on the optimum timing for postoperative adjustment after strabismus surgery. We wanted to compare 2 common practices of adjustable suture technique after strabismus surgery. METHODS: Two comparable groups of 40 patients each, who had strabismus surgery with adjustable suture technique, were prospectively studied. Group A had early adjustment the same day of the surgery about 6 hours after the operation, and group B had late adjustment the next day about 24 hours after the operation. Subjective scoring tables were used to evaluate the pain felt by the patient before, during, and after the adjustment and any difficulties of the adjustment process. Requirements of postoperative pain medications and final alignment 6 weeks after surgery were also compared. RESULTS: Despite adequate statistical power, no significant differences were found between the groups regarding pain before, during, and after adjustment, difficulties performing the adjustment, and final alignment after 6 weeks (P > .05). Both adjustment schedules were equally associated with mild to moderate pain before, during, and after the adjustment. In the first 24 hours after surgery, no overall difference in the use of pain medications was found. Nausea and vomiting in the first 24 postoperative hours were more common in the early adjustment group (P = .02). CONCLUSION: The surgeon can feel free to choose the timing for postoperative adjustment. However, when performing an early adjustment, the surgeon should be especially prepared to control nausea and vomiting.

Adult↗
PubMed2001

Indocyanine green angiography of the anterior segment in patients undergoing strabismus surgery.

BACKGROUND: Anterior segment imaging using fluorescein angiography is only suitable in lightly pigmented irides as the brown pigmentation of the iris masks fluorescein transmission. Indocyanine green (ICG) angiography has excellent penetration of pigment epithelium and, therefore, has potential application in detecting perfusion changes of dark irides after strabismus surgery. METHODS: A prospective study was conducted on patients older than 15 years undergoing strabismus surgery. A fundus camera was focused on the arteriolar tufts of the pupillary margin and 50 mg of ICG (concentration of 12.5 mg/ml) was given intravenously. Images were then obtained at 1 minute intervals of 5 minutes' duration. RESULTS: 45 patients with a mean age of 54.6 years and a mean follow up period of 8.6 weeks were studied. There were 23 patients in the primary surgery group, 11 in the secondary surgery group, and 11 in the staged group. Iris ICG angiograms were successfully performed in all patients. No persistent filling defect was detected in the primary and secondary horizontal recti surgery groups or in the secondary or staged vertical and combined vertical rectus groups 6-8 weeks postoperatively. 57% of both primary vertical and combined vertical and horizontal groups showed defects in the early postoperative phase. Only three cases demonstrated late perfusion defects in this series. CONCLUSION: ICG can detect iris perfusion changes in dark irides after strabismus surgery. Iris reperfusion was achieved in the majority of the cases.

Adolescent↗
PubMed2000

Genetic and clinical features of hemoglobin H disease in Chinese patients.

BACKGROUND: Normally, one pair of each of the two alpha-globin genes, alpha1 and alpha2, resides on each copy of chromosome 16. In hemoglobin H disease, three of these four alpha-globin genes are affected by a deletion, a mutation, or both. We studied the alpha1-globin gene abnormalities and the clinical and hematologic features of Chinese patients with hemoglobin H disease in Hong Kong. METHODS: We assessed the clinical features, hematologic values, serum ferritin levels, and liver function of 114 patients with hemoglobin H disease. We also performed echocardiography and magnetic resonance imaging of the liver and examined the two pairs of alpha-globin genes. RESULTS: Hemoglobin H disease in 87 of the 114 patients (76 percent) was due to the deletion of three of the four alpha-globin genes (--/-alpha), a combination termed the deletional type of hemoglobin H. The remaining 27 patients (24 percent) had the nondeletional type of hemoglobin H disease, in which two alpha-globin genes are deleted and a third is mutated (--/alphaalphaT). All 87 patients with the deletional type of hemoglobin H were double heterozygotes in whom there was a deletion of both alpha-globin genes from one chromosome, plus a deletion of the alpha1 or alpha2 gene from the other chromosome (--/alpha- or --/-alpha). A variety of mutated alpha-globin genes was found in the patients with nondeletional type of hemoglobin H disease. Patients with the nondeletional type of the H disease had more symptoms at a younger age, more severe hemolytic anemia, and larger spleens and were more likely to require transfusions than patients with deletional hemoglobin H disease. The severity of iron overload was not related to the genotype. CONCLUSIONS: Chinese patients in Hong Kong with the nondeletional type of hemoglobin H disease have more severe disease than those with the deletional type of the disease. Iron overload is a major cause of disability in both forms of the disease.

Adolescent↗
PubMed2000

Rapid identification of Pseudomonas aeruginosa from ocular isolates by PCR using exotoxin A-specific primers.

The purpose of this research was to evaluate the use of PCR for the identification of ocular isolates of Pseudomonas aeruginosa by using primers specific to the exotoxin A gene of the bacteria. Genomic DNA was obtained from ocular microbial isolates of keratitis patients. Primers were designed based on the published sequence of the exotoxin A gene of P. aeruginosa. Using the primers designed, PCR reactions were performed on the DNA samples. The PCR was also examined for its specificity and sensitivity. In addition, a direct PCR using heating method was attempted on P. aeruginosa with no separate DNA extraction step. ATCC strains of P. aeruginosa were included as positive controls. The rest of the bacteria other than P. aeruginosa served as negative controls. A single band was obtained when analysed on agarose gel electrophoresis only from samples that contained genomic DNA of P. aeruginosa. The direct PCR method was also successful with the same band produced from the amplification. The whole process was completed within 4 h. The direct PCR amplification targeting at the exotoxin A gene of P. aeruginosa is potentially a rapid, specific, sensitive and relatively simple method for the identification of ocular isolates of P. aeruginosa.

ADP Ribose Transferases↗
PubMed2000

Endogenous bacterial endophthalmitis: an east Asian experience and a reappraisal of a severe ocular affliction.

PURPOSE: To report 32 eyes of 27 patients with endogenous bacterial endophthalmitis seen over a 4 year period. Features and outcomes of this condition in the current series and the cases reported in the literature from 1986-1998 were reviewed. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: All patients with this condition seen at the three participating general hospitals were included. INTERVENTION: A review of the systemic and ocular characteristics, therapeutic methods, and final outcomes in patients afflicted with this condition. MAIN OUTCOME MEASURES: Features studied included patients' demographic characteristics, microbiology, source of infection, ocular features, therapeutic interventions, final visual and anatomic outcomes. RESULTS: Nineteen (70%) of the 27 incriminating organisms in this case series were gram negative microbes, with Klebsiella pneumoniae infections alone being responsible in 16 (60%) cases. Hepatobiliary tract infection was the source of bacteremia in 13 (48%) patients. Only nine (28%) eyes obtained good final visual acuity (20/120 or better), and two eyes were enucleated/eviscerated. A literature review of 209 patients with endogenous endophthalmitis over a 12 year period showed a similar increase in the frequency of gram negative microbes as the responsible organism, especially among the East Asian population. Overall, 22% had bilateral involvement; two thirds of patients had predisposing factor(s) or underlying illness(es), and diabetes mellitus was present in 46%. Thirty-four percent of all eyes obtained counting finger or better final vision, and 16% had their eyes eviscerated or enucleated. Infections with virulent organisms (gram negative rods, Serratia, Bacillus) usually denoted a grave visual prognosis; however, a media that was not opaque on presentation was usually associated with a good prognosis. CONCLUSION: Metastatic ocular infection is not uncommon despite the availability of modern antibiotic therapy. Among the East Asian population, the patient at highest risk is a diabetic patient with Klebsiella pneumoniae hepatobiliary infection. In contrast, in the Caucasian population, this condition occurs in predisposed patients with gram-positive bacteremia arising from endocarditis or skin/joint infections. The final visual outcome in patients with endogenous bacterial endophthalmitis in the recent 12 years has not differed significantly from five decades ago.

Adult↗
PubMed2000

Single nucleotide polymorphisms of the factor IX gene for linkage analysis in the southern Chinese population.

Carrier detection and prenatal testing for haemophilia B in Oriental populations have been hampered by the lack of informative markers within the factor IX (FIX) gene. We detected a T/C nucleotide variation at nucleotide 32770 in the poly-A region of the FIX gene in the mother of a haemophilia B child. Analysis of 139 unrelated alleles revealed a heterozygosity rate of 0.193, thus offering an additional marker for linkage analysis. Together with two other polymorphic sites (5' MseI and 3' HhaI) found in Chinese and Thai populations, these polymorphisms were useful in 66% of the families studied.

China↗
PubMed2000

Eye cancer incidence in Singapore.

AIM: To describe the epidemiological characteristics of patients with primary intraocular, conjunctival, and orbital cancers seen in Singapore from 1968 to 1995. METHODS: Epidemiological data of all cancers diagnosed in Singapore are collected by the Singapore Cancer Registry. The data of all cases of Singapore residents with eye cancers (ICD-9, site 190) were retrieved for analysis. This includes intraocular, conjunctival, and orbital cancers but excludes cancer of the eyelids. RESULTS: There were 125 patients of which 67 (53.6%) were male and 58 (46.4%) were female. The average annual age standardised incidences for male and female Singapore residents were 1.89 and 1.81 per million respectively. The most common cancer was retinoblastoma (53.6%), followed by malignant melanoma (19.2%) and squamous cell carcinoma (11.2%). The most common cancer among patients younger than 15 years was retinoblastoma (95.7%) and that for those 15 years and older was malignant melanoma (42.6%). The most common subsite was the retina (53.6%), followed by conjunctiva (12.8%), orbit (8.8%), and lacrimal gland (6.4%). CONCLUSION: The annual age standardised incidence have been stable for the 28 years studied. Retinoblastoma is much more common than melanoma in Singapore. These expanded epidemiological characteristics serve to provide ophthalmologists and epidemiologists with a foundation to monitor future disease patterns in Singapore and provide a basis for comparison with other selected populations elsewhere.

Adolescent↗