Taken together, we present a family with closely related parents with two children suffering of severe forms of monogenic juvenile arthritis caused by homozygous variants within FAMIN. In line with the previously described cases of FAMIN-related familial systemic and polyarticular JIA, the reported association with other inflammatory and infectious diseases, respectively, as well as the currently published pathophysiological role of FAMIN, these cases add evidence for a causative role of the alterations in the development of these inflammatory phenotypes. This evidence concerns the gene LACC1 and polyarticular juvenile idiopathic arthritis.