The calibration curves of the drugs show excellent linearity over a concentration ranges: 0.20–13.0 μg/mL for PHO, 0.50–20.0 μg/mL for EPH and 0.70–20.0 μg/mL for GUA with LOQ values of 0.18, 0.38 and 0.50. The gene discussed is EPHA1; the disease is primary hypertrophic osteoarthropathy.