Comparison of real-time PCR and nested PCR for the detection of Y chromosome sequences in the peripheral blood mononuclear cells of patients with systemic sclerosis

genotype and response to MTX. Differences in study design and patient population may account for the lack of agreement between our results and those of Rizzo et al. Rizzo et al examined patients starting MTX and defined response as a reduction in DAS44 .0.6 at 6 months. Although our study was cross-sectional in design, if there was a significant contribution of HLA-G genotype to MTX response, one would expect this to be evident. Furthermore, one might anticipate the dose of MTX to be lower in patients homozygous for the deletion allele if HLA-G genotype influenced MTX response. Although the power of this study was only sufficient to detect a fairly substantial difference in response rates between genotype groups (.30%), there are no indications from the data of an increased response rate in the HLA-G 2/214 bp genotype group. Rizzo et al examined patients with early RA (median duration 20–22 months) compared to median duration of 10 years in our study. Patients with RA may be less responsive to MTX later in the disease. Alternatively, it is possible that soluble HLA-G (sHLA-G) influences early MTX treatment but other factors are involved in determining long-term response to this drug. Although the exact mechanism by which MTX exerts its anti-inflammatory effect remains unclear, multiple pathways are involved and it is possible that variation in other genes within these pathways may influence MTX response. L K Stamp, J L O’Donnell, P T Chapman, M L Barclay, M A Kennedy, C M A Frampton, R L Roberts 1 Department of Rheumatology, Immunology and Allergy, Christchurch Hospital, Christchurch, New Zealand; 2 Department of Medicine, University of Otago, Christchurch, New Zealand; 3 Department of Clinical Pharmacology, Christchurch Hospital, Christchurch, New Zealand; 4 Department of Pathology, University of Otago, Christchurch, New Zealand