Possible gene dosage effect of glutathione-S-transferases on atopic asthma: Using real-time PCR for quantification of GSTM1 and GSTT1 gene copy numbers

Asthma is a complex genetic disorder characterized by chronic inflammation in the airways. As oxidative stress is a key component of inflammation, variations in genes involved in antioxidant defense could therefore be likely candidates for asthma. Three enzymes from the superfamily glutathione‐S‐transferase (GST) involved in the antioxidant defense were tested for association to asthma using 246 Danish atopic families in a family‐based transmission disequilibrium test (TDT) design. A real‐time PCR assay for relative quantification of gene copy number of GSTM1 and GSTT1 was developed. The assay made it possible to distinguish individuals with zero, one, and two copies and thereby to investigate whether the GST genes influenced susceptibility to asthma in a dose‐dependent manner. We found that asthmatic patients with two copies of GSTM1 were significantly underrepresented (p