Based on this hypothesis and the newest studies by Horovitz et al., showing recessive inheritance of rare NOD2 variants in 7–10% of CD cases and indicating NOD2 as a Mendelian disease gene for early-onset CD [23], we aimed to estimate the frequency of c.802C>T, c.2104C>T, c.2722G>C, c.2798 + 158C>T, and c.3019_3020insC variants in a cohort of Polish IBD patients, including children. The gene discussed is NOD2; the disease is inflammatory bowel disease.