Among 54 adults with Crohn disease evaluated before anti-TNF-α treatment, we found only 3.7% of TST+QFT+ patients (2/54), a prevalence which remains quite low (V. Corbière, personal communication), whereas the prevalence of positive TST among TB contacts reaches 30% in Belgium (V. Sizaire, FARES – personal communication). The gene discussed is TNF; the disease is tuberculosis.