Chiu Yeung Chan

Genetic association between a chemokine gene CXCL-10 (IP-10, interferon gamma inducible protein 10) and susceptibility to tuberculosis

n Abstractn n Backgroundn Previous studies showed that activation of CXCL-10 and other chemokines were prominent in many infectious diseases. These chemokines are components of innate immune response to respiratory tract pathogens. We examined the promoter variants of CXCL-10 and their role in predisposition to tuberculosis (TB).n n n Methodsn The promoter 1.8kb of CXCL-10 was sequenced in 24 healthy Chinese individuals to identify genetic polymorphisms. Three tagging SNPs in CXCL-10 promoter (−1447A>G, −872G>A, −135G>A) were selected, and genotyping were performed in 240 TB patients and 176 healthy Chinese subjects. Disease associations were examined by χn n 2n and Fisher exact test.n n n Resultsn A promoter SNP (−135G>A) with minor allele frequency of 0.1 showed a moderate association with TB both in genotype analysis (p=0.01) and allelic analysis (p=0.03); other tagging SNPs (−1447A>G, −872G>A) were not associated with TB. The odd ratio of the protective allele −135G>A was 0.51(C.I 0.29 −0.91) for homozygotes and heterozygotes carriers of the A allele.n n n Conclusionn A new potential protective SNP (−135G>A) for TB is identified in the promoter of chemokine gene, CXCL-10. Interestingly, the exact same allele has been shown to enhance IP-10 transactivation and susceptibility to Hepatitis B virus infection in a recent publication. This SNP, located at 14bp upstream of a NF-kB binding site, might also account for the susceptibility to TB. Our results expanded the clinical significance of this SNP in CXCL-10 promoter.n n

Rapid diagnosis of smear-negative pulmonary tuberculosis via fibreoptic bronchoscopy: utility of polymerase chain reaction in bronchial aspirates as an adjunct to transbronchial biopsies

Fibreoptic bronchoscopy was performed on 190 patients with chest radiographic lesions and negative sputum smears for acid-fast bacilli. Aside from obtaining transbronchial biopsies for histological examination, bronchial aspirate specimens were also tested for Mycobacterium tuberculosis complex DNA by a conventional polymerase chain reaction (PCR) technique. Of 177 transbronchial biopsies performed, a diagnosis was found in 64 cases [43 cases of tuberculosis (TB), 17 cases of lung carcinoma and four cases of other infective/inflammatory diseases] giving a diagnostic yield of 36.2%. PCR was positive in 105 of 108 finally diagnosed cases of TB and 22 of 82 non-TB cases. The sensitivity, specificity, positive predictive value and negative predictive value of PCR when applied to bronchial aspirate specimens for diagnosing smear-negative pulmonary TB were 97.2%, 73.2%, 82.7% and 95.2% respectively. Therefore, detection of M. tuberculosis complex DNA in bronchial aspirates by PCR might have an adjunctive place to transbronchial biopsies in the rapid diagnosis of smear-negative pulmonary tuberculosis.

Association of polymorphisms in the Chr18q11.2 locus with tuberculosis in Chinese population.

A GWAS study has reported that two single nucleotide polymorphisms (SNPs) were associated with predisposition to tuberculosis (TB) in African populations. These two loci represented the long-waited GWAS hits for TB susceptibility. To determine whether these two SNPs are associated with TB in Chinese population, we attempted an replication in a cohort of over one thousand Chinese TB patients and 1,280 healthy controls using melting temperature shift allele-specific genotyping analysis. We found that only SNP rs4331426 was significantly associated with TB in Chinese population (pxa0=xa00.011). However, the effect was opposite. The G allele of the SNP in Chinese population is a protective allele (ORxa0=xa00.62, 95xa0% CIxa00.44–0.87), while it was the risk allele for African population (ORxa0=xa01.19, 95xa0% CIxa01.12–1.26). No significance was found for SNP rs2335704. The results provided an independent support for a role in susceptibility to TB for SNP rs4331426. However, it also indicated that direct predisposition element to TB and the association effects may vary across ethnic groups.

Two cases of Nocardia asteroides sternotomy infection treated with ofloxacin and a review of other active antimicrobial agents

Two patients who developed post-operative sternotomy infections due to Nocardia asteroides were treated successfully with ofloxacin, in vitro susceptibility of the organisms being used as a guide to dosage. The place of this drug in the treatment of infection due to Nocardia asteroides merits further investigation.

A Tuberculostearic Acid Assay in the Diagnosis of Sputum Smear-Negative Pulmonary Tuberculosis: A Prospective Study of Bronchoscopic Aspirate and Lavage Specimens

OBJECTIVEnTo determine whether the detection of tuberculostearic acid (TBSA) in bronchial aspirate and bronchoalveolar lavage specimens is useful for the rapid diagnosis of active pulmonary tuberculosis in patients suspected of having the disease.nnnSETTINGnA pulmonary clinic in a teaching hospital.nnnPATIENTSnForty patients suspected of active pulmonary tuberculosis but who failed to produce sputum or whose sputum smears were negative for acid-fast bacilli on at least 3 occasions, 29 of whom were subsequently confirmed to have tuberculosis. A group of 13 patients who were having fiberoptic bronchoscopy for other reasons served as controls.nnnINTERVENTIONnAll patients had fiberoptic bronchoscopy; bronchial aspirate, bronchoalveolar lavage, and sputum specimens were obtained when possible.nnnMEASUREMENTS AND MAIN RESULTSnAll specimens were examined microscopically for acid-fast bacilli, cultured for mycobacteria, and assayed for TBSA by gas chromatography and mass spectrometry with selected ion monitoring. Only 4 of the 29 patients with tuberculosis were diagnosed by direct microscopy compared with 26 by TBSA assay. In 2 patients who required surgical biopsy for conventional diagnosis, the TBSA test was positive. There were no false-positive TBSA results in the 13 controls, but 2 of 5 sputum specimens from the 11 test patients in whom tuberculosis was excluded were falsely positive, probably because of contamination with mouth flora. Because sputum can rarely be obtained from these patients and may give false-positive results, it is not a good specimen for TBSA assay. Sensitivities and specificities of the test for the other specimens were as follows: aspirate, 0.52 (CI, 0.32 to 0.71) and 1.00 (CI, 0.75 to 1.00); lavage, 0.68 (CI, 0.46 to 0.85) and 1.00 (CI, 0.84 to 1.00); aspirate and lavage combined, 0.79 (CI, 0.60 to 0.92) and 1.00 (CI, 0.86 to 1.00).nnnCONCLUSIONSnThe TBSA assay for bronchial aspirate and bronchoalveolar lavage fluid is useful for rapidly diagnosing smear-negative pulmonary tuberculosis. In these specimens it is highly specific and more sensitive than microscopy. This assay could be used to diagnose other mycobacterial infections, however, it cannot distinguish among species.

Determinants of serum 1,25-dihydroxyvitamin D concentration in healthy premenopausal subjects

Concentrations of serum phosphate and parathyroid hormone (PTH) are well known regulators of the production of 1,25-dihydroxyvitamin D (1,25-(OH)2D) and acidosis is known to affect the serum concentration of 1,25-(OH)2D. However, the factors that play a role in the regulation of serum 1,25-(OH)2D concentration in healthy subjects have not been fully evaluated. The associations of ionised calcium, pH, serum concentration of phosphate, PTH, 25-hydroxyvitamin D (25-OHD) and serum 1,25-(OH)2D were examined in 296 healthy premenopausal women (age range 17-40 years). Calculation of partial correlation coefficients showed that serum 1,25-(OH)2D was significantly correlated with phosphate (r = -0.148, P < 0.01), pH (r = 0.221, P < 0.001) and PTH (r = 0.136. P < 0.01). Ionised calcium was not related to serum 1,25-(OH)2D. When the results were stratified according to quartiles based on serum 1,25-(OH)2D concentration, significant trends (by analysis of variance) were seen in phosphate, pH, age, albumin and 25-OHD. Stepwise multiple regression analysis showed that phosphate and pH were the major contributors of serum 1,25-(OH)2D levels. There was a small contribution from PTH and 25-OHD. The results suggest that in young healthy premenopausal women plasma phosphate and pH may be important determinants of serum 1,25-(OH)2D concentration.

Rapid diagnosis of mycobacterial infections

Tuberculostearic acid ([R]-10-methyloctadecanoic acid [TBSA] ) is a structural component of mycobacteria, and its detection in appropriate clinical specimens has potential application as a rapid screening method for the presence of Mycobacterium tuberculosis and other mycobacteria. We used the highly sensitive technique of gas chromatography-mass spectrometry (GC-MS) combined with selected ion monitoring (SIM) of m/e 312 and m/e 167 to detect TBSA in clinical specimens collected in Hong Kong, where tuberculosis is still common. The test was useful for the diagnosis of M. tuberculosis in sputum, pleural aspirates, bronchial washings, CSF and tissue biopsies. The test was highly specific and more sensitive than conventional microscopy, and more rapid but rather less sensitive than conventional culture methods.