Autosomal dominant mutations in FAM111A are causative for Kenny-Caffey syndrome type 2. Patients with Kenny-Caffey syndrome suffer from severe growth retardation, skeletal dysplasia, hypoparathyroidism, hypocalcaemia, hyperphosphataemia and hypomagnesaemia. While recent studies have reported FAM111A to function in antiviral response and DNA replication, its role in regulating electrolyte homeostasis remains unknown. In this study, we assessed the role of FAM111A in the regulation of serum electrolyte balance using a Fam111a knockout (Fam111a−/−) C57BL/6 N mouse model. Fam111a−/− mice displayed normal weight and serum parathyroid hormone (PTH) concentration and exhibited unaltered magnesium, calcium and phosphate levels in serum and 24-hour urine. Expression of calciotropic (including Cabp28k, Trpv5, Klotho and Cyp24a1), magnesiotropic (including Trpm6, Trpm7, Cnnm2 and Cnnm4) and phosphotropic (Slc20a1, Slc20a2, Slc34a1 and Slc34a3) genes in the kidneys, duodenum and colon were not affected by Fam111a depletion. Only Slc34a2 expression was significantly upregulated in the duodenum, but not in the colon. Analysis of femurs showed unaffected bone morphology and density in Fam111a−/− mice. Kidney and parathyroid histology were also normal in Fam111a−/− mice. In conclusion, our study is the first to characterise the function of FAM111A in vivo and we report that mice lacking FAM111A exhibit normal electrolyte homeostasis on a standard diet.

Transcellular magnesium (Mg2+) reabsorption in the distal convoluted tubule (DCT) of the kidneys plays an important role in maintaining systemic Mg2+ homeostasis. SLC41A1 is a sodium (Na+)-Mg2+ exchanger that mediates Mg2+ efflux from the cells and is hypothesized to facilitate basolateral extrusion of Mg2+ in the DCT. In this study, we generated a SLC41A1 knockout mouse model to examine the role of SLC41A1 in Mg2+ homeostasis. Slc41a1-/- mice exhibited similar serum and urine Mg2+ levels as their wildtype littermates. Dietary restriction of Mg2+ resulted in a reduced serum Mg2+ concentration and urinary Mg2+ excretion, which was similar in the wildtype and the knockout groups. Expression of genes encoding Mg2+ channels and transporters Trpm6, Trpm7, Cnnm2 and Slc41a3 were unchanged based on genotype. We investigated potential redundancy of SLC41A1 and its homologue SLC41A3 by generating a double knockout mouse. While Slc41a3-/- knockout mice showed significantly reduced serum Mg2+ compared to wildtype and Slc41a1-/- knockout groups, double knockout mice displayed similar serum Mg2+ levels as the single Slc41a3-/- knockout mice. In conclusion, our data shows that SLC41A1 is not involved in the regulation of systemic Mg2+ homeostasis in mice. Our data also demonstrate that SLC41A1 does not compensate for the loss of SLC41A3, suggesting different functions of these SLC41 proteins in vivo.

Context Kenny-Caffey syndrome (KCS) is a rare hereditary disorder characterized by short stature, hypoparathyroidism and electrolyte disturbances. KCS1 and KCS2 are caused by pathogenic variants in TBCE and FAM111A, respectively. Clinically the phenotypes are difficult to distinguish. Objective The objective was to determine and expand the phenotypic spectrum of KCS1 and KCS2 in order to anticipate on complications that may arise in these disorders. Design We clinically and genetically analyzed ten KCS2 patients from seven families. Because we found unusual phenotypes in our cohort, we performed a systematic review of genetically confirmed KCS cases using PubMed and Scopus. Evaluation by three researchers led to the inclusion of 26 papers for KCS1 and 16 for KCS2, totaling 205 patients. Data were extracted following the Cochrane guidelines and assessed by two independent researchers. Results Several patients in our KCS2 cohort presented with intellectual disability (3/10) and chronic kidney disease (6/10), which are not considered common findings in KCS2. Systematic review of all reported KCS cases showed that the phenotypes of KCS1 and KCS2 overlap for postnatal growth retardation (KCS1: 52/52, KCS2: 23/23), low PTH levels (121/121, 16/20), electrolyte disturbances (139/139, 24/27), dental abnormalities (47/50, 15/16), ocular abnormalities (57/60, 22/23) and seizures/spasms (103/115, 13/16). Symptoms more prevalent in KCS1 included intellectual disability (74/80, 5/24), whereas in KCS2 bone cortical thickening (1/18, 16/20) and medullary stenosis (7/46, 27/28) were more common. Conclusions Our case series established chronic kidney disease as a new feature of KCS2. In literature, we found substantial overlap in the phenotypic spectra of KCS1 and KCS2, but identified intellectual disability and the abnormal bone phenotype as the most distinguishing features.

Context Kenny-Caffey syndrome (KCS) is a rare hereditary disorder characterized by short stature, hypoparathyroidism and electrolyte disturbances. KCS1 and KCS2 are caused by pathogenic variants in TBCE and FAM111A, respectively. Clinically the phenotypes are difficult to distinguish. Objective The objective was to determine and expand the phenotypic spectrum of KCS1 and KCS2 in order to anticipate on complications that may arise in these disorders. Design We clinically and genetically analyzed ten KCS2 patients from seven families. Because we found unusual phenotypes in our cohort, we performed a systematic review of genetically confirmed KCS cases using PubMed and Scopus. Evaluation by three researchers led to the inclusion of 26 papers for KCS1 and 16 for KCS2, totaling 205 patients. Data were extracted following the Cochrane guidelines and assessed by two independent researchers. Results Several patients in our KCS2 cohort presented with intellectual disability (3/10) and chronic kidney disease (6/10), which are not considered common findings in KCS2. Systematic review of all reported KCS cases showed that the phenotypes of KCS1 and KCS2 overlap for postnatal growth retardation (KCS1: 52/52, KCS2: 23/23), low PTH levels (121/121, 16/20), electrolyte disturbances (139/139, 24/27), dental abnormalities (47/50, 15/16), ocular abnormalities (57/60, 22/23) and seizures/spasms (103/115, 13/16). Symptoms more prevalent in KCS1 included intellectual disability (74/80, 5/24), whereas in KCS2 bone cortical thickening (1/18, 16/20) and medullary stenosis (7/46, 27/28) were more common. Conclusions Our case series established chronic kidney disease as a new feature of KCS2. In literature, we found substantial overlap in the phenotypic spectra of KCS1 and KCS2, but identified intellectual disability and the abnormal bone phenotype as the most distinguishing features.