Disruption of the c‐terminal serine protease domain of Fam111a does not alter calcium homeostasis in mice

Abstract FAM111A gene mutations cause Kenney–Caffey syndrome (KCS) and Osteocraniostenosis (OCS), conditions characterized by short stature, low serum ionized calcium (Ca 2+ ), low parathyroid hormone (PTH), and bony abnormalities. The molecular mechanism mediating this phenotype is unknown. The c‐terminal domain of FAM111A harbors all the known disease‐causing variations and encodes a domain with high homology to serine proteases. However, whether this serine protease domain contributes to the maintenance of Ca 2+ homeostasis is not known. We hypothesized the disruption of the serine protease domain of FAM111A would disrupt Ca 2+ homeostasis. To test this hypothesis, we generated with CRISPR/Cas9, mice with a frameshift insertion (c.1450insA) or large deletion (c.1253‐1464del) mutation in the Fam111a serine protease domain. Serum‐ionized Ca 2+ and PTH levels were not significantly different between wild type, heterozygous, or homozygous Fam111a mutant mice. Additionally, there were no significant differences in fecal or urine Ca 2+ excretion, intestinal Ca 2+ absorption or overall Ca 2+ balance. Only female homozygous (c.1450insA), but not heterozygous mice displayed differences in bone microarchitecture and mineral density compared to wild‐type animals. We conclude that frameshift mutations that disrupt the c‐terminal serine protease domain do not induce a KCS or OCS phenotype in mice nor alter Ca 2+ homeostasis.