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Biomedical subjects

I S Ng

Publications and source records attributed to I S Ng.

18 recordsLinked to original sources
PubMed2006

Genetic analysis of SCA2, 3 and 17 in idiopathic Parkinson's disease.

Recent reports of SCA2 and SCA3 patients who presented with levodopa responsive parkinsonism have generated considerable interest as they have implications for genetic testing. It is unclear whether ethnic race alone or founder effects within certain geographical region explain such an association. In this study, we conducted genetic analysis of SCA2, 3, 17 in an ethnic Chinese cohort with early onset and familial Parkinson's disease (PD) and healthy controls. A total of 191 subjects comprising of 91 PD and 100 healthy controls were examined. We identified one positive case of SCA2 in an early-onset sporadic PD patient who had CAG 36 repeats, yielding a prevalence of 2.2% in early-onset sporadic PD patients and less than 1.0% in our study PD population. The size of the repeats was lower than the expanded repeats (38-57) in SCA2 patients with ataxia in our population. All the children of the patient were physically normal even though some of them carried the repeat expansion of similar size. No cases and controls were positive for SCA3 and SCA17. We do not think routine screening of SCA2, SCA3 and SCA17 for all idiopathic PD patients is cost-effective in our ethnic Chinese population. However, SCA2 should be a differential diagnosis in young onset sporadic PD when genetic mutations of other known PD genes have been excluded.

Adult↗
PubMed2004

Fragile X premutation alleles in SCA, ET, and parkinsonism in an Asian cohort.

Among 367 subjects, the authors analyzed 167 patients with essential tremor, sporadic progressive cerebellar ataxia, multiple-system atrophy, and atypical parkinsonism and 200 healthy control subjects for FMR1 premutation alleles. None of the subjects carried alleles within the premutation range. These findings suggest that in the absence of other supportive clinical or imaging features, the cost-effectiveness of routine fragile X tremor/ataxia syndrome screening in this Asian cohort with movement disorders was low.

Adult↗
PubMed2001

Trinucleotide repeat analysis of Huntington's disease gene in Singapore.

INTRODUCTION: Huntington's disease (HD) is an inherited neurodegenerative disorder characterised by chorea and progressive dementia. The mutation causing the disease has been identified as an unstable expansion of a trinucleotide (CAG)n. We have assessed the (CAG)n repeats in the patients and controls in our population. MATERIALS AND METHODS: Polymerase chain reactions (PCRs) for the repeat region were carried out for 116 individuals: 10 were asymptomatic at-risk members from 5 families; 53 symptomatic patients from various hospitals; and 53 normal unrelated Singaporeans. Estimation of the number of repeats was based on Metaphor gel electrophoresis, sizing using the GeneScan on ABI 310 Genetic Analyzer, and sequencing using the same equipment. RESULTS: Metaphor gel sizing generally gives an over-estimation, and GeneScan gives an under-estimation of repeat numbers compared with sequencing which is the gold standard. Of the 63 patients and family members tested, 25 had one expanded allele of 40 to 54 CAG repeats and the other allele in the normal range of 15 to 30 repeats. One patient had an allele in the intermediate range (38). CONCLUSION: The range of CAG repeats in the normal and HD alleles in our population is similar to those reported elsewhere. An accurate sizing can only be obtained with sequencing. For allele sizes in the intermediate range (37-40), sequencing should be carried out to confirm the carrier status of a patient.

Adolescent↗
PubMed2000

Novel germline BRCA1 mutations detected in women in singapore who developed breast carcinoma before the age of 36 years.

BACKGROUND: In recent years, although BRCA1 has been extensively investigated, the contribution of inherited BRCA1 mutations to breast carcinoma in Asian populations is largely unknown. The authors undertook this study to determine the prevalence and spectrum of germline BRCA1 mutations among women in Singapore with early onset breast carcinoma. METHODS: Forty-three of 72 eligible patients whose breast carcinoma was diagnosed before the age of 36 years were studied, independent of family history. DNA samples from 50 unrelated individuals randomly selected from the National Thalassemia Registry served as controls. Mutational screening was performed by single-strand conformation polymorphism analysis and protein truncation test, and alterations were confirmed by sequencing. First-degree relatives of patients with definite BRCA1 mutations were offered screening. RESULTS: A total of 6 novel alterations in BRCA1 were identified, including 2 frameshift mutations in exon 11 (2846insA and 2885delA), 3 rare sequence variants, and 1 polymorphism. Three women (7%) carried deleterious mutations, and the mutation was present in at least 1 unaffected first-degree relative of the proband. The same mutation (2846insA) was identified in 2 of the 7 unrelated subjects of Malay ethnicity. One mutation and three rare variants were identified in four women with no family history of breast or ovarian carcinoma whereas all women with affected first-degree relatives did not harbor BRCA1 mutations. No mutation was identified in the controls. CONCLUSIONS: The spectrum of germline BRCA1 mutations among the patients in this study was distinct from that in Caucasian populations although a similar prevalence was observed. Larger studies are necessary to clarify the significance of the mutation 2846insA in the Malay community and the penetrance of specific mutations in the Singapore population.

Adult↗
PubMed2000

DNA testing for fragile X syndrome in 255 males from special schools in Singapore.

INTRODUCTION: Fragile X syndrome, the most common cause of inherited mental retardation, results from unstable expansion of a trinucleotide (CGG)n repeat in the FMR1 gene. Phenotypic expression is variable making clinical diagnosis difficult, while diagnosis by Southern blotting is relatively expensive and labour intensive. The prevalence in Singapore has not been studied. MATERIALS AND METHODS: We developed a rapid screening test using a PCR analysis. We studied 255 males with unexplained cause for learning difficulties from 8 special schools. A clinical scoring system based on characteristic features described was devised. RESULTS: PCR analysis showed absence of the band for the normal allele in 11 samples, 6 of which were confirmed by Southern blotting to be positive for FMR1 expansion, giving a 2% false-positive rate with PCR. Sensitivity of the PCR test was evaluated by performing Southern blotting in all PCR-normal samples; all of which were confirmed to be normal. This PCR test was shown to be highly reproducible. Clinical criteria were not predictive. CONCLUSIONS: Six (2.4%) new cases of fragile X syndrome were detected. There is a need to incorporate fragile X testing in routine screening of patients with developmental delay and learning difficulties. The use of PCR could eliminate the need for Southern blotting in up to 95% of cases. PCR analysis provides a simple, reliable and rapid tool for screening.

Adolescent↗
PubMed1997

Variants of chromosome 9 in phenotypically normal individuals.

The human chromosome 9 displays the highest degree of structural variability. Four different types of variants are described including pericentric inversion, extra G-positive band in the q arm, additional G-positive band in the p arm and duplication of band 9q21-q22. It is important to demonstrate inheritance from a phenotypically normal individual in order to differentiate between a variant chromosome and an abnormal chromosome.

Azure Stains↗
PubMed1997

Williams syndrome--the Singapore General Hospital experience.

Williams syndrome first described in 1961 is generally characterised by mental deficiency, gregarious personality, unusual "elfin" facies, supravalvular aortic stenosis and idiopathic infantile hypercalcaemia. Patients with Williams syndrome show a hemizygous submicroscopic deletion of 7q11.23 detectable by fluorescent in-situ hybridisation (FISH). The deleted portion of the chromosome corresponds to the Elastin gene. We report 3 girls with characteristics of Williams syndrome in whom the diagnosis was confirmed by demonstration of the hemizygous deletion of 7q11.23 in the karyotype by FISH. These patients, aged 6, 7 and 10 years, showed the characteristic facies and gregarious personalities. Some developmental delay with mild mental deficiency and dysmorphic facies were prominent features in the initial presentation. Cardiac lesions found in these patients were small patent ductus arteriosus which closed, pulmonary valvular stenosis and mitral valve prolapse associated with mitral regurgitation respectively. Hypercalcaemia was not documented in these patients. Learning difficulty was a major issue and all patients required special schooling. Chromosome analyses done on peripheral blood were found to be normal in all patients. FISH using the Elastin Williams Syndrome Chromosome Region (WSCR) probes (oncor) showed the hemizygous deletion of 7q11.23. Diagnosis of Williams syndrome can now be confidently confirmed with the help of FISH.

Child↗
PubMed1996

Subtle translocation (18;21) confirmed by FISH in a patient with Down syndrome.

The patient presented with the typical features of Down syndrome; hypotonia, brachycephaly, flattened occiput, bilateral prominent medical epicanthic folds, flat nasal bridge, protruding tongue, low-set dysplastic ears, short broad hands, bilateral clinodactyly and simian crease. The karyotype of this child was originally reported as normal. High-resolution chromosomes revealed extra material on the long arm of chromosome 18. The mother's karyotype showed a reciprocal translocation between the long arm of 18 and the long arm of 21 at band q23 and q22.1, respectively. FISH performed separately with two different 21q cosmid probes gave two signals on the mother's metaphases and three signals on the proband. These findings confirmed that the proband is trisomic for the long arm of chromosome 21 at loci D21S65 and D21S19.

Chromosomes, Human, Pair 18↗
PubMed1996

Molecular heterogeneity of beta-thalassaemia in Malaysia: a practical approach to diagnosis.

The beta-thalassaemia mutations in 20 Malaysian children with beta-thalassaemia major were characterised by using a multi-modal approach, consisting of a slot-blot hybridisation with selected allele-specific oligonucleotides (ASO), followed by reverse dot-blot assay (RDB), amplification refractory mutation system (ARMS) and genomic sequencing. This strategy yielded a 94.4% mutation detection rate. The 6 most common mutations were codons 41/42 (-TTCT), IVS II nt 654(C --> T), IVS I nt 5(G --> C), IVS I nt 1(G -->T), codon 35 (-C) and codon 19 (A --> G), which accounted for 83.3% of all mutations detected. A strategy of initial screening with the above 6 selected ASOs for slot-blot hybridisation followed by RDB assay for the less common Asian mutations would give a mutation identification of 91.7%. Another feasible approach would be to analyse alleles from a particular racial group, by a judicious selection of 4 ASOs common to that particular subpopulation and then supplement this with RDB assay. This could yield a 100% coverage for the Chinese subpopulation in Malaysia. With these strategies, a practical approach has been identified to overcome the pitfalls posed by the molecular heterogeneity of beta-thalassaemia to enable prenatal diagnosis and carrier screening to be carried out. Regional collaborative studies are to be encouraged as an indispensable tool in providing better health care services to our patients.

Asian People↗
PubMed1996

Early prenatal diagnosis of beta-thalassaemia in Singapore.

beta-thalassaemia is one of the commonest autosomal recessive genetic diseases in the Singapore population. In the homozygous form, it results in a severe anaemia, requiring monthly transfusion for survival. Because of the less than satisfactory treatment available for the condition, prenatal diagnosis has always been an option for couples at-risk. The available method was globin chain analysis of foetal blood, obtained at 18 to 20 weeks of gestation. Affected pregnancies would then be diagnosed and require termination in the mid to late trimester. A relatively newer technique, chorionic villus sampling (CVS), allows foetal material to be obtained in the first trimester. However, analysis of the foetal tissue requires direct gene studies to be performed. The aim of this study was to evaluate the feasibility of this analysis in couples at-risk for beta-thalassaemia in Singapore. Sixteen couples who were at-risk for a child with beta-thalassaemia major were offered prenatal diagnosis. All of them opted for CVS as compared to foetal blood sampling. The mutations in the beta-globin gene in these couples at-risk were identified. Direct gene analysis was then performed on the foetal sample, using a variety of molecular techniques. These included reverse dot-blot hybridisation, allele-specific oligonucleotide hybridisation, restriction enzyme digests and direct analysis of amplified products. DNA profiling was done for each case to exclude definitively the possibility of maternal tissue contaminating the foetal sample. The results in all these cases were unequivocal. The procedure of CVS itself was uneventful in these 16 couples. Procedural-associated foetal loss was nil. Prenatal diagnosis in the first trimester allows early termination of an affected pregnancy with significantly less maternal morbidity and prenatal anxiety. It also results in greater patient acceptability of the procedure and plays a key role in the prevention of this devastating genetic disease.

Chorionic Villi Sampling↗
PubMed1995

Del(3) (p25.3) without phenotypic effect.

A terminal deletion of chromosome 3 at p25.3 was observed during prenatal diagnosis. A similar deletion is also present in the phenotypically normal mother. The deletion was confirmed by FISH. The breakpoint is distal to the region responsible for the 3p- syndrome. A normal baby girl was born with no apparent phenotypic abnormalities.

Adult↗
PubMed1994

Beta-thalassemia mutations in Singapore--a strategy for prenatal diagnosis.

The strategy for early prenatal diagnosis of beta-thalassemia in Singapore by direct detection of the mutant beta-globin gene requires the spectrum of mutations producing the disorder in this population to be characterized. We analyzed 134 beta-thalassemia alleles from Singapore by specific oligonucleotide hybridization after DNA amplification, using a nonradioactive enhanced chemiluminescence detection system. The mutations were identified in 90% of the alleles using five oligonucleotide probes for the following mutations: codons 41/42 (deletion-TCTT), IVS II nt 654 (C-->T), codon 17 (A-->T), IVS I nt 5 (G-->C), and -28 TATA box (A-->G). Together with the strategy of direct sequencing, a total of 97% of the mutations were identified. In the Chinese subpopulation, 97% of the mutations were detected by the oligonucleotide probes. Using just four oligonucleotide probes would identify 96% of the mutations, and 76% of the mutations were accounted for by codon 41/42 (-TCTT) and IVS II nt 654 (C-->T) mutations. Thus in this subpopulation early prenatal diagnosis would be possible in virtually all the affected families.

Alleles↗
PubMed1993

Deletion of the terminal segment of the long arm of chromosome 4 with aortic stenosis.

A dysmorphic Chinese baby girl was found to have deletion of the long arm of chromosome 4 (46XX, del[4] q33-->qter). A review of various case reports of deletion of the long arm of chromosome 4 is reported and the clinical features are identified and compared. The earlier reports on this condition were that of deletion of the terminal segment of the long arm with break point occurring at q31. Since 1981, cases of deletion with break point at q33 have been reported.

Abnormalities, Multiple↗
PubMed1993

Huntington's disease: recent progress in gene mapping and potential local application in Singapore.

Advances in the field of molecular genetics have made testing of individuals for the presence of certain genes possible. Programmes for testing families with Huntington's disease have been developed overseas but not locally. We outline our beginning attempts to make services such as prenatal exclusion testing and presymptomatic carrier detection available to Singapore families with Huntington's disease.

Chromosome Mapping↗
PubMed1993

Huntington's disease in five siblings.

Huntington's disease is an autosomal dominant neurodegenerative condition which is rare in Singapore. Five siblings with progressive chorea and dementia were treated at the Singapore General Hospital and followed up over a seven-year period. Family history revealed five deceased affected individuals, two living affected siblings and more than 35 "at risk" offspring spanning another two generations each with about a 50% probability of carrying the Huntington's disease gene. We believe this is the largest kindred with Huntington's disease in Singapore.

Adult↗
PubMed1991

Methods for analysis of multiple cystic fibrosis mutations.

A large number of mutations causing cystic fibrosis (CF) have been reported. In an attempt to improve methods for genetic diagnosis and for heterozygote screening, we evaluated methods for efficient analysis of the delta F508, G542X, G551D, R553X, and N1303K mutations. We found that multiple mutations can be analyzed simultaneously using hybridization with allele-specific oligonucleotides. Alternatively all of these mutations can be detected by amplification of DNA followed by restriction enzyme digestion and analysis on polyacrylamide gels. A previously reported method for use of modified primers for DNA amplification to allow detection of virtually any single-base change by restriction enzyme analysis proved particularly useful. The common delta F508 mutation and three mutations in exon 11 were analyzed using a multiplex amplification reaction followed by double digestion with restriction enzymes and electrophoresis in a single lane on a polyacrylamide gel. In a sample of 439 CF chromosomes from North American Caucasians, the frequencies of various mutations were as follows: delta F508 = 75.8%, G542X = 2.7%, G551D = 3.2%, R553X = 1.4%, and N1303K = 1.4% for a total of 84.5% detection of CF chromosomes by analysis for these five mutations.

Base Sequence↗