Homozygosity mapping and whole-exome sequencing in an IO IBD patient and subsequent sequencing of the candidate gene in 12 additional IO IBD patients revealed two patients with two mutated ankyrin repeat and zinc-finger domain-containing 1 (<i>ANKZF1</i>) alleles (homozygous <i>ANKZF1</i> R585Q mutation and compound heterozygous <i>ANKZF1</i> E152K and V32_Q87del mutations, respectively) and two patients with one mutated <i>ANKZF1</i> allele.