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

FAM111A gene mutations cause Kenney-Caffey syndrome (KCS) and Osteocraniostenosis (OCS), conditions characterized by short stature, low serum ionized calcium (Ca²⁺), 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 Ca²⁺ homeostasis is not known. We hypothesized the disruption of the serine protease domain of FAM111A would disrupt Ca²⁺ 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 Ca²⁺ 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 Ca²⁺ excretion, intestinal Ca²⁺ absorption or overall Ca²⁺ 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 Ca²⁺ homeostasis.