Displaying publications 1 - 20 of 55 in total

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  1. Yap SF
    Malays J Pathol, 2004 Jun;26(1):1-12.
    PMID: 16190102
    "Parenteral" or "serum" hepatitis is known to have afflicted man for centuries. However, it was not until the mid-1960s that the causative agent of this infection, the hepatitis B virus, was discovered. Since then, the biology and the replication strategy of the virus, and the clinical features and the epidemiology of the hepatitis B infection have been determined. Knowledge about the virus and the infection it causes led to the development of firstly, a plasma-derived vaccine and later a recombinant vaccine for the prevention of the infection. Integration of the hepatitis B vaccine into newborn vaccination programmes on a worldwide basis represents a major step in the effort to eliminate this infectious disease and its complications. Laboratory tests are available for the diagnosis and monitoring of the disease. Therapies have been developed to halt the progress of the chronic infection in affected individuals. While these developments have resulted in a decrease of the frequency of infection in many countries, particularly those that have implemented universal immunization of newborns, the chronic infection remains a significant global problem. Worldwide, over 300 million individuals are infected and each year, an estimated 1 million persons die from chronic complications of the disease including hepatocellular carcinoma and hepatic failure. The therapies currently available result in elimination of the virus in only a relatively small proportion of subjects and carry with it serious side effects. Geopolitical, economic and other factors hinder the vision of elimination of the infection through immunization programmes. Nevertheless, work continues to clarify further the underlying pathological mechanism of the infection, the host and viral factors that promote elimination or persistence of the virus in the human host. It is hoped that such investigations will reveal viral targets for the design of newer and potentially more effective drugs to treat the infection.
  2. Yap SF
    Malays J Pathol, 1994 Jun;16(1):3-6.
    PMID: 16329567
    Chronic hepatitis B virus (HBV) infection constitutes a major public health problem particularly in developing countries in East Asia, South-East Asia, the Pacific Basin and Africa. In Malaysia, a developing nation in the South East Asian region, the chronic HBV carrier rate varies between < 1% to about 10% depending on the ethnic group studied. The highest frequency is seen among the Chinese, followed by the Malays and lastly the Indians, with a male preponderance of between 2 : 1 and 3 : 1. Exposure to the virus among the adult population is estimated to be about 15%, 26% and 36% among the Indians, Malays and Chinese respectively. Serological study of adult chronic HBV carriers showed a frequency of HBe antigenemia of about 35%, with a significant decreasing trend with age. HBV DNA status generally correlated with the HBe status. An atypical profile of anti-HBe associated with serum HBV DNA is found in some carriers; in most instances, this is related to seroconversion from HBe antigenemia to anti-HBe. Chronic complications of HBV infection include the development of hepatocellular carcinoma (HCC), the occurrence of which closely parallel that of HBsAg carrier rate. In Malaysia, HCC is the third most common malignant neoplasm and among the 10 leading causes of death. About 80% of our HCC cases are HBV associated. All 3 ethnic groups are afflicted, the highest frequency being among the Chinese. Males show a disproportionate risk with an odds ratio of 3.93 (p < 0.0001).
  3. Pavai S, Yap SF
    Med J Malaysia, 2003 Dec;58(5):667-72.
    PMID: 15190651
    The tumour marker CA19-9 is a sensitive marker for pancreatic, gastric and hepatobiliary malignancies. High CA 19-9 level indicates unresectable lesions and a poor prognosis. The objective of the study was to determine the significance and implications of elevated CA 19-9 levels in the serum. A one-year retrospective review of all patients who had CA19-9 measured in our Medical Centre was undertaken; 69 patients were found to have CA 19-9 level above the cut-off value (37 U/ml). Thirty-six patients had malignant and the remaining 33 had benign lesions. CA 19-9 was found to be elevated in malignancies of pancreas, colorectum, lung, liver and ovary. Benign conditions associated with elevation of CA 19-9 included disease of the hepatobiliary system, pneumonia, pleural effusion, renal failure and SLE. In two individuals, there was no obvious cause for the elevation of this marker. CA 19-9 levels were significantly lower in benign than in malignant conditions. In conclusion, elevated CA 19-9 may be found in patients with benign as well as malignant disease. Therefore, it is important (1) that elevated levels of CA 19-9 are interpreted in the light of the clinical presentation of the patient and (2) to be aware of the benign conditions that can be associated with increased levels of this marker. With these factors in mind, CA 19-9 can be used to assist in the diagnosis of pancreatic cancer and assessment of resection adequacy post-operatively.
  4. Yap SF, Pang T
    Asian J Infect Dis, 1979 Jun;3(2):85-7.
    PMID: 120736
    Serum C3 and C4 values were determined in 236 normal adults of three racial groups, using the single radial immunodiffusion techniques. The C3 levels varied from 47 to 119 mg/dl and C4 levels from 16 to 66 ml/dl (mean +/- 2SD). The values were found to be comparable to the normals reported in some Western series. No significant differences in the levels related to sex and race were found.
  5. Yap SF, Wong PW, Kenneth-Raj
    Br J Biomed Sci, 1994 Dec;51(4):336-40.
    PMID: 7756940
    A study was carried out to determine optimal assay conditions for an in-house hybridisation assay for detection of hepatitis B virus (HBV) genome in serum samples. Pre-treatment of samples, blot treatment and hybridisation conditions were found to affect assay performance. The indirect serum blot procedure was more robust and reliable than direct serum blotting. In the former, viral particles were isolated from the sample, lysed and then extracted. In comparison, no approaches to the direct serum spot method performed adequately. Sensitivity studies showed that labelling of the nucleic acid probe with dCTP was more efficient than with dATP. Using probes labelled to a specific activity of > 1 x 10(8) and an autoradiography period of about 48 h we could achieve a detection limit of < 1 pg. Specificity was achieved by use of a highly purified probe and moderately stringent hybridisation and wash conditions. Background binding was minimal and there was no non-specific binding of probe to negative control samples. Factors affecting speed of the assay were studied to identify steps that could be modified to shorten assay time without sacrificing performance. A shorter centrifugation step and the use of a high specific-activity probe permitted completion of an assay within four days.
  6. Yap SF, Peh SC
    Malays J Pathol, 1991 Dec;13(2):115-8.
    PMID: 1726642
    Serum alpha-fetoprotein (AFP) levels and its expression in liver tissue was studied in 50 cases of histologically confirmed hepatocellular carcinoma (HCC). Serum AFP levels were elevated (greater than 20iu/ml) in 35/50 (70%) of the cases, 28 of whom had levels greater than 500 iu/ml, which is highly suggestive of HCC. These results indicate that serum AFP, by itself, is a relatively insensitive diagnostic test for HCC. Although elevated levels in high risk patients provide a specific clue, a negative result does not exclude the diagnosis of HCC. Expression of AFP by tumour cells paralleled that of serum in the majority of cases. However, tissue AFP was negative in 7 patients who had markedly elevated serum AFP. This observation may be a reflection of preferential excretion of the tumour antigen or differential expression of the antigen by the tumour cells. None of the patients with normal serum AFP demonstrated a reaction for tissue AFP. There was no correlation between AFP production and tumour differentiation.
  7. Jeyamalar R, Pathmanathan R, Yap SF, Kannan P
    Ann Acad Med Singap, 1991 Nov;20(6):795-7.
    PMID: 1803972
    Cardiac amyloidosis is an uncommon and often unrecognised cause of cardiac failure. It is an infiltrative disease that may mimic either a restrictive or hypertrophic cardiomyopathy, constrictive pericarditis, coronary artery disease or valvular heart disease. The diagnosis should be suspected in a patient with cardiac failure who has low voltage complexes on the electrocardiogram, in association with increased myocardial mass and echogenicity on the echocardiogram. The definitive diagnosis, however, can only be made by endomyocardial biopsy or biopsy of any involved organ in systemic amyloidosis. Prognosis is poor and treatment ineffective.
  8. Ruiz Estrada MA, Yap SF, Park D
    Disasters, 2014 Jul;38 Suppl 2:S206-29.
    PMID: 24905816 DOI: 10.1111/disa.12069
    Natural hazards have a potentially large impact on economic growth, but measuring their economic impact is subject to a great deal of uncertainty. The central objective of this paper is to demonstrate a model--the natural disasters vulnerability evaluation (NDVE) model--that can be used to evaluate the impact of natural hazards on gross national product growth. The model is based on five basic indicators-natural hazards growth rates (αi), the national natural hazards vulnerability rate (ΩT), the natural disaster devastation magnitude rate (Π), the economic desgrowth rate (i.e. shrinkage of the economy) (δ), and the NHV surface. In addition, we apply the NDVE model to the north-east Japan earthquake and tsunami of March 2011 to evaluate its impact on the Japanese economy.
  9. Lee WS, Yap SF, Looi LM
    J Paediatr Child Health, 2007 Sep;43(9):636-9.
    PMID: 17688648
    We conducted a prospective study to determine the role of alpha1-antitrypsin (alpha1AT) deficiency in the pathogenesis of neonatal cholestasis and other childhood liver diseases in a multi-ethnic Southeast Asian population.
  10. Sthaneshwar P, Prathibha R, Yap SF
    Malays J Pathol, 2005 Jun;27(1):29-32.
    PMID: 16676690
    Thyrotoxic periodic paralysis (TPP) is a medical emergency characterised by sudden onset of muscle weakness with hypokalemia that resolves with the treatment of hyperthyroidism. We report three cases of thyrotoxic periodic paralysis seen at the Accident and Emergency Care Department, University of Malaya Medical Centre in a period of four months. We also review the clinical presentation, pathophysiology, biochemical features and management of TPP. All three patients were young Asian males, presenting with muscle weakness of sudden onset. The first patient presented with lower limb weakness and had symptoms of thyrotoxicosis and goitre. He had a previous similar episode which resolved spontaneously. The second patient presented with quadriplegia, respiratory acidosis and had no signs and symptoms of thyrotoxicosis. The electrocardiogram of this patient showed normal sinus rhythm with U wave in V3 and a flat T wave, which are characteristic of hypokalaemia. The third patient, who was a known case of thyrotoxicosis, was admitted thrice for hypokalemic paralysis during the study period. All cases had low serum potassium, suppressed TSH and elevated T4 confirming thyrotoxic periodic paralysis. Potassium therapy was useful during the crisis; however prophylactic potassium has not been shown to prevent attacks as seen in one of our cases.
  11. Sthaneshwar P, Yap SF, Jayaram G
    Malays J Pathol, 2002 Jun;24(1):53-8.
    PMID: 16329556
    Pleural effusion is a common diagnostic problem. The analysis of serum and pleural fluid for tumour markers is widely used as a diagnostic aid in clinical practice. The aim of the present study was to determine the usefulness of simultaneous quantification of carcinoembryonic antigen (CEA) and carbohydrate antigen (CA-125) in distinction of malignant from benign effusion. Data from a total of 78 patients including 53 patients with benign and 25 patients with malignant effusion was evaluated. The cut-off values for differentiating benign from malignant effusions were determined using results obtained from patients with known benign effusions (mean + 2 SD, 95% confidence interval). The cut-off for CEA and CA-125 were 5.1 ng/ml and 1707 IU/ml respectively. CEA assay in pleural fluid had an acceptable sensitivity and good specificity of 64% and 98% respectively. CA-125 had a sensitivity of 36% and specificity of 94%. The combination of the two tumour markers gave a sensitivity of 72% and specificity of 92.4%. We suggest a good clinical strategy may be to begin with CEA measurement (assay specificity 98%); if CEA is below the cut-off value (negative), CA-125 could then be measured to improve the sensitivity of detection of malignant effusions. However, measurement of these tumour markers is not cost effective from the point of view that it does not give information on the type of malignancy present. The latter has to be determined either by histological or cytological study.
  12. Looi LM, Yap SF, Cheah PL
    Ann Acad Med Singap, 1997 Nov;26(6):750-3.
    PMID: 9522973
    Fresh frozen neoplastic tissues from 70 infiltrating ductal breast carcinomas were analysed for cytosolic oestrogen receptor (ER) protein content using a solid phase enzyme immunoassay (EIA) method based on a "sandwich" principle (Abbott ER-EIA monoclonal). Formalin-fixed, paraffin-embedded sections from the same carcinomas were examined for nuclear immunoreactivity against a monoclonal antibody for ER protein (Dako) using the standard avidin-biotin complex immunoperoxidase (IP) method after microwave antigen retrieval. The degree of ER positivity by IP was also scored according to a visual estimation of the percentage of cells expressing immunopositivity and the intensity of staining. Twenty-eight (40%) of the carcinomas were ER-positive by EIA and 34 (48.6%) were positive by IP. Twenty-five (35.7%) were ER-positive and 33 (47.1%) were ER-negative by both methods. Nine (12.9%) were ER-negative by EIA but were positive by IP, this discrepancy being ascribed to sampling inadequacy for EIA. However, 3 (4.3%) tumours were ER-positive by EIA and negative by IP. This discrepancy may be variously due to inadequate antigen retrieval, faulty technique and the possibility that the two methods do not measure identical ER proteins. IP appears to have an advantage over EIA in that it has a higher pick-up rate, does not require fresh tissue and can be applied to archival material. However, to reduce false negative estimations, it may be necessary to run IP staining using more than one ER antibody. Standardisation of the IP method for ER is desirable before this method is to be widely adopted in Malaysian laboratories. Quantitation of ER positivity by IP scoring correlated poorly with actual cytosolic levels. Caution should be exercised in attaching patient management value to visual IP scoring.
  13. Looi LM, Cheah PL, Yap SF
    Malays J Pathol, 1997 Jun;19(1):35-9.
    PMID: 10879240
    One hundred and twelve infiltrating ductal carcinoma of breast were studied by the standard avidinbiotin complex immunoperoxidase method on formalin-fixed, paraffin-embedded tissue sections, using a monoclonal antibody to c-erbB-2 oncoprotein. The same tumours were assessed and scored according to the Bloom and Richardson criteria into three histological grades. The distribution of tumours according to grade were: 8 Grade I, 34 Grade II and 70 Grade III. Forty-three (38.4%) tumours showed positive membrane staining for c-erbB-2 oncoprotein. These comprised 7 Grade II and 36 Grade III tumours with c-erbB-2 immunopositivity rates of 20.6% and 51.4% respectively. The oncoprotein was not expressed by Grade I tumours. This study shows a good correlation between c-erbB-2 expression and histological grade, a known prognostic indicator of invasive breast carcinoma. Because the c-erbB-2 oncogene has extensive structural homology to the epidermal growth factor receptor gene, its overexpression can be expected to result in more aggressive tumour behaviour. While it may be regarded as another indicator of poor prognosis breast cancers, its value in the selection of carcinomas less responsive to hormonal therapy and those more suitable for immunotherapy than chemotherapy has been mooted but remains to be clarified.
  14. Yap SF, Wong NW, Goh KL
    Malays J Pathol, 1994 Jun;16(1):57-62.
    PMID: 16329577
    The relationship between serum Hepatitis B virus DNA (HBV-DNA) and the Hepatitis B e-antigen/ anti-Hepatitis Be (HBeAg/anti-HBe) serological status in Malaysians was studied. 212 cases of asymptomatic HBV carriers were recruited for this study. 92 cases were positive for the HBeAg at the point of recruitment. 85 (92.4%) of these patients tested positive for HBV-DNA, of whom 55 (64.7%) had levels over 100pg/ml of serum. Three of the remaining 7 HBeAg positive cases who were negative for HBV-DNA subsequently seroconverted. The other 4 cases remained negative for HBV-DNA for periods of 6-12 months. Out of 113 cases who were anti-HBe positive, 12 (10.6%) gave a positive HBV-DNA result. 2 of these 12 patients were recent seroconverters; the remaining cases had transiently increased viral replicative activity which later subsided. 7 out of the 212 carriers were in the e-window period; all 7 tested negative for HBV-DNA. Our data confirm a high frequency of HBV-DNA in HBeAg positive carriers and a negative correlation between HBV-DNA and anti-HBe. An atypical profile of anti-HBe associated with HBV-DNA was observed in 10.6% of the carriers. An inverse relationship between serum HBV-DNA levels and age was also observed.
  15. Lim WM, Yap SF, Makkar M
    J Bus Res, 2021 Jan;122:534-566.
    PMID: 33012896 DOI: 10.1016/j.jbusres.2020.08.051
    The proliferation of home sharing in the extant marketing and tourism literature has only been accelerated in recent times due to the emergence of the sharing economy. This paper contends that it is now an opportune time to pursue a stock take of existing knowledge in order to guide future marketing and tourism research on home sharing. Therefore, the goal of this paper is to review and propose an agenda for home sharing from a marketing and tourism perspective. Through a framework-based systematic review, this paper offers an organized, retrospective view of the antecedents, decisions, and outcomes (ADO) of home sharing in marketing and tourism. The paper also provides a snapshot on the theories, contexts, and methods (TCM) employed to gain this understanding before concluding with a discussion on the extant knowledge gaps and the ways in which these gaps could be addressed through pertinent ideas for future marketing and tourism research on home sharing.
  16. Nasir NM, Sthaneshwar P, Yunus PJ, Yap SF
    Malays J Pathol, 2010 Jun;32(1):21-6.
    PMID: 20614722 MyJurnal
    The objective of the study is to determine the level of agreement between measured total carbon dioxide (TCO2) and calculated bicarbonate (HCO3-) in our laboratory.
  17. Thong MK, Tan JA, Tan KL, Yap SF
    J Trop Pediatr, 2005 Dec;51(6):328-33.
    PMID: 15967770 DOI: 10.1093/tropej/fmi052
    beta-thalassaemia major, an autosomal recessive hemoglobinopathy, is one of the most common single gene disorders in multi-racial Malaysia. The control of beta-thalassaemia major requires a multi-disciplinary approach that includes population screening, genetic counselling, prenatal diagnosis and the option of termination of affected pregnancies. To achieve this objective, the molecular characterisation of the spectrum of beta-globin gene mutations in each of the affected ethnic groups is required. We studied 88 consecutive unrelated individuals and their respective families with beta-thalassaemia (74 beta-thalassaemia major, 12 HbE-beta-thalassaemia, 2 with HbE homozygotes) and four individuals with beta-thalassaemia trait that contributed a total 180 alleles for study. Using a 2-step molecular diagnostic strategy consisting of amplification refractory mutation system (ARMS) to identify the 8 most common mutations followed by other DNA-based diagnostic techniques, a total of 177 (98.3 per cent) of the 180 beta-thalassaemia alleles were characterised. One out of 91 (1 per cent) of the Chinese alleles, one out of 46 (2.2 per cent) Malay alleles and one out of two Indian alleles remained unknown. A 100 per cent success rate was achieved in studying the Kadazandusun community in this study. A strategy to identify beta-globin gene mutations in Malaysians with beta-thalassaemia is proposed based on this outcome.
  18. Yap SF, Wong PW, Chen YC, Rosmawati M
    PMID: 12118437
    A retrospective study was carried out to determine the frequency of the pre-core stop codon mutant virus in a group of chronic hepatitis B carriers: 81 cases were considered [33 hepatits B e antigen (HBe) positive and 48 HBe negative]. All of the HBe positive cases had detectable viral DNA by hybridization analysis; in the case of the HBe negative cases, one third had detectable viral DNA by hybridization analysis and two thirds had HBV DNA detectable by polymerase chain reaction (PCR) amplification. Pre-core stop codon mutant detection was carried out on all specimens using allele-specific oligonucleotide hybridization following PCR amplification of the target sequence. The pre-core mutant was detected in 13/33 (39.4%) of HBe positive cases and in 32/48 (66.7%) of HBe negative cases. Sequence analysis was carried out on 8 of the 16 HBe negative specimens that did not carry the pre-core mutant virus to determine the molecular basis for the HBe minus phenotype in these cases: the 1762/1764 TA paired mutation in the second AT rich region of the core promoter was detected in five cases; a start codon mutation was detected in one case. The predominant mutation resulting in the HBe minus phenotype in our isolates was the 1896A pre-core ("pre-core stop codon") mutation; other mutations responsible for the phenotype included the core promoter paired mutation and pre-core start codon mutation. In view of the high frequency of the pre-core mutant virus, sequence analysis was performed to determine the virus genotype on the basis of the nucleotide sequence of codon 15. The sequences of 21 wild type virus (14 HBe positive and 7 HBe negative cases) were examined: 15 were found to be codon 15 CCT variants (71.4%); the frequency in the HBe positive group was 12/14 (85.7%), while that in the HBe negative group was 3/7 (42.9%). The high frequency of the codon 15 CCT variant in association with the frequent occurrence of the pre-core mutant in our isolates concurs with the results of other studies.
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