• PNX KO mice show normal fertility and estrous cycle lengths, indicating that the absence of PNX does not affect reproductive function.• Both wildtype and knockout mice respond similarly when placed on a high-fat diet. Nonetheless, the male heterozygous mice gain slightly less weight.• Male KO mice exhibit some changes in energy homeostasis-related genes, such as melanocortin receptor 4 (Mc4r), but no changes in reproduction-related genes in the hypothalamus.• Female KO mice travel less distance in the outer zone of an open field test, suggesting alterations in anxiety or locomotor behavior. Here, SMIM20 is linked to Anxiety.