FCN3 and Immunodeficiency: Thus, the common variant associated with Ficolin-3 plasma levels identified in this work, rs2504780 (AF = 10.7%, 1:27710876, T>A), is located 9.5kb upstream of FCN3 and associated with a diminution of Ficolin-3 levels (effect size = − 3.79 μg/mL per alternative allele, Fig. 6A) of an order of magnitude comparable with heterozygous FCN3 loss-of-function variants (effect size = − 13.4 μg/mL per loss-of-function allele) [86] causing immunodeficiency 41 with lymphoproliferation and autoimmunity (OMIM 606367) [87–92].