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Proteases are critical enzymes in cellular processes which regulate intricate events like cellular proliferation, differentiation and apoptosis. This review highlights the multifaceted roles of the serine proteases FAM111A and FAM111B, exploring their impact on cellular functions and diseases. FAM111A is implicated in DNA replication and replication fork protection, thereby maintaining genome integrity. Additionally, FAM111A functions as an antiviral factor against DNA and RNA viruses. Apart from being involved in DNA repair, FAM111B, a paralog of FAM111A, participates in cell cycle regulation and apoptosis. It influences the apoptotic pathway by upregulating anti-apoptotic proteins and modulating cell cycle-related proteins. Furthermore, FAM111B’s association with nucleoporins suggests its involvement in nucleo-cytoplasmic trafficking and plays a role in maintaining normal telomere length. FAM111A and FAM111B also exhibit some interconnectedness and functional similarity despite their distinct roles in cellular processes and associated diseases resulting from their dysfunction. FAM111A and FAM111B dysregulation are linked to genetic disorders: Kenny–Caffey Syndrome type 2 and Gracile Bone Dysplasia for FAM111A and POIKTMP, respectively, and cancers. Therefore, the dysregulation of these proteases in diseases emphasizes their potential as diagnostic markers and therapeutic targets. Future research is essential to unravel the intricate mechanisms governing FAM111A and FAM111B and explore their therapeutic implications comprehensively.

Background/Objectives: FAM111A is a trypsin-like serine protease that has emerged as a regulator of DNA replication, and is directly related to genome stability, protein homeostasis, antiviral defense and cancer progression. Pathogenic variants in FAM111A are correlated with genetic syndromes such as Kenny–Caffey syndrome type 2 (KCS2) and gracile bone dysplasia/osteocraniostenosis (GCLEB/OCS). This study focuses on the evolutionary, genetic, and structural analysis of FAM111A, in order to identify key regions and candidate pharmacological targets that are related to this enzyme’s function. Methods: The methodology of this in silico study includes separate analyses at the sequence, structural and functional levels. Initially, data mining was carried out using NCBI/Protein (2025), and then data filtering was performed in order to identify representative FAM111A sequences for several species. Sequence analysis was then executed through multiple alignments and phylogenetic analyses. Through this, conserved domains and motifs were identified. For structural analysis, human pathogenic mutations and protein structures were identified through searches in biological databases including PDB and ClinVar, and then all data were analyzed in order to identify candidate pharmacological targets related to FAM111A function. Results: Approximately 1850 FAM111A protein sequences were retrieved for several species, and after filtering processes a dataset of 85 representative sequences was generated. Evolutionary analysis indicates that FAM111A originated in early metazoans, with progressive domain specialization leading to mammal-restricted acquisition of regulatory elements, including the PIP-box PCNA (proliferating cell nuclear antigen) interacting peptide and UBL (ubiquitin-like) domains. The ubiquitin-like/DNA binding domain and catalytic serine protease domain (SPD) are the most conserved, containing seven highly conserved motifs. The structural analysis was based on two protein structures and 34 critical mutations that accumulate in two distinct regions. Finally, by combining the results, six pharmacological targets and 100 inhibitors are proposed. Conclusions: Advancing the structural and function characterization of FAM111A, coupled with pharmacological target identification and evolutionary insights, will be critical to validate this underexplored protease as a therapeutic genetic target in genetic disorders, cancer, and antiviral responses.

Background Although interferon regulatory factor 2 (IRF2) was reported to stimulate virus replication by suppressing the type I interferon signaling pathway, because cell cycle arrest was found to promote viral replication, IRF2-regulated replication fork factor (FAM111A and RFC3) might be able to affect ZIKV replication. In this study, we aimed to investigate the function of IRF2, FAM111A and RFC3 to ZIKV replication and underlying mechanism. Methods siIRF2, siFAM111A, siRFC3 and pIRF2 in ZIKV-infected A549, 2FTGH and U5A cells were used to explore the mechanism of IRF2 to inhibit ZIKV replication. In addition, their expression was analyzed by RT-qPCR and western blots, respectively. Results In this study, we found IRF2 expression was increased in ZIKV-infected A549 cells and IRF2 inhibited ZIKV replication independent of type I IFN signaling pathway. IRF2 could activate FAM111A expression and then enhanced the host restriction effect of RFC3 to inhibit replication of ZIKV. Conclusions We speculated the type I interferon signaling pathway might not play a leading role in regulating ZIKV replication in IRF2-silenced cells. We found IRF2 was able to upregulate FAM111A expression and thus enhance the host restriction effect of RFC3 on ZIKV.

Kenny-Caffey syndrome (KCS) is a rare autosomal recessive (AR)/dominant disease characterized by hypoparathyroidism, skeletal dysplasia, dwarfism, and dysmorphism. or TBCE gene mutations are responsible for this syndrome. Osteocraniostenosis (OCS) is a lethal syndrome with similar features to KCS, and it can be a severe form of KCS type 2 which results from the gene mutation. The mutation is generally characterized by the autosomal dominant transition. We present a male case having compound heterozygous variants (c.976T>A and c.1714_1716del) in the gene with an AR inheritance pattern. Hypocalcemia developed on the second day of life. The patient and his older sister had a dysmorphic face, skeletal dysplasia, and they were diagnosed with hypoparathyroidism. Both siblings died due to septicemia. He is the first reported patient with the mutation in Turkey. The phenotype of the patient is compatible with OCS, and the detected variants may explain the disease genetically.

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.

Background/Objectives: Kenny–Caffey syndrome 2 (KCS2) is a rare cause of hypoparathyroidism, inherited in an autosomal dominant mode, resulting from pathogenic variants of the FAM111A gene, which is implicated in intracellular pathways regulating parathormone (PTH) synthesis and skeletal and parathyroid gland development. Methods: The case of a boy is reported, presenting with the characteristic and newly identified clinical, biochemical, radiological, and genetic abnormalities of KCS2. Results: The proband had noticeable dysmorphic features, and the closure of the anterior fontanel was delayed until the age of 4 years. Biochemical evaluation at several ages revealed persistent hypocalcemia, high normal phosphorous, and inappropriately low normal PTH. To exclude other causes of short stature, the diagnostic approach revealed low levels of IGF-1, and on CNS MRI, small pituitary gland and empty sella. Nocturnal levels of growth hormone were normal. MRI also revealed bilateral symmetrical microphthalmia and torturous optic nerves. Skeletal survey was compatible with cortical thickening and medullary stenosis of the long bones. Genomic data analysis revealed a well-known pathogenic variant of the FAM111A gene (c.1706G>A, p. R569H), which is linked with KCS2 or nanophthalmos. Conclusions: KCS2, although a rare disease, should be included in the differential diagnosis of hypoparathyroidism and short stature. Understanding the association of pathogenic variants with KCS2 phenotypic variability will allow the advancement of clinical genetics and personalized long-term follow-up and will offer insights into the role of the FAM111A gene in the disease pathogenesis and normal embryogenesis of implicated tissues and organs.

Background/Objectives: Hypoparathyroidism (HPT) is a disorder caused by the insufficient production of parathyroid hormone (PTH). Its main features include decreased serum calcium, increased serum phosphorus, and abnormal bone modeling. In children, HPT is most commonly due to genetic disorders. Among rare genetic syndromes that can include HPT in their clinical spectrum is Kenny–Caffey syndrome (KCS) type 2. Conventional therapy for HPT primarily consists of oral calcium and active vitamin D metabolites. The major limitation of conventional therapy is hypercalciuria with an increased risk of nephrocalcinosis. However, a subset of patients fails to achieve the desired therapeutic response to conventional treatment; the reasons for this remain incompletely understood in some cases. The failure to achieve therapeutic targets and persistent hypercalciuria are the main indications for considering therapy with recombinant human parathyroid hormone (rhPTH). Methods: In addition to the review of the literature on rhPTH use in pediatric hypoparathyroidism, the first application of rhPTH in the treatment of genetically caused HPT in a child with Kenny–Caffey syndrome type 2 (KCS2) was described. Results: In this paper, we present a two-month-old infant who received rhPTH for 14 months. A heterozygous de novo p.Ser541Pro variant in the FAM111A gene was identified through whole-genome sequencing, indicating a diagnosis of KCS2. A biological mechanism linking FAM111A protein function with a more profound disruption of parathyroid development or function was proposed, suggesting that rhPTH therapy may be particularly beneficial in KCS2 cases. Conclusions: This is the first reported use of rhPTH in a child in Serbia and the first reported use in KCS type 2. By reviewing the literature, we analyzed the conditions in which rhPTH has been used, dosing approaches and durations, requirements for concomitant conventional therapy during rhPTH treatment, and the effects of rhPTH on calciuria. We provide an overview of rhPTH use in children. Additionally, based on the pathogenic genetic variant responsible for KCS2 in our patient, we propose possible etiologic explanations. This work aims to encourage a consideration of rhPTH use in children following its official approval.

Background Kenny–Caffey syndrome type 2 (KCS2) is an extremely rare inherited disorder characterized by proportionate short stature, skeletal defects, ocular and dental abnormalities, and transient hypocalcemia. It is caused by variants in FAM111A gene. Diagnosis of KCS2 can be challenging because of its similarities to other syndromes, the absence of clear hallmarks and the deficient number of genetically confirmed cases. Here, we aimed to further delineate and summarize the genotype and phenotype of KCS2, in order to get a better understanding of this rare disorder, and promote early diagnosis and intervention. Methods We present clinical and genetic characteristics of eight newly affected individuals with KCS2 from six families, including one family with three individuals found to be a father‐to‐daughter transmission, adding to the limited literature. Furthermore, we performed a review of genetically confirmed KCS2 cases in PubMed, MEDLINE and CNKI databases. Results There were six females and two males in our cohort. All the patients presented with short stature (100.0%). Clinical manifestations included ocular defects such as hypermetropia (5/8), dental problems such as defective dentition (3/8) and dental caries (3/8), skeletal and brain anomalies such as delayed closure of anterior fontanelle (6/8), cerebral calcification (3/8), cortical thickening (3/8) and medullary stenosis (4/8) of tubular bones. Endocrinologic abnormalities included hypoparathyroidism (5/8) and hypocalcemia (3/8). One male patient had micropenis and microorchidism. All cases harboured missense variants of FAM111A, and nucleotides c.1706 arose as a mutational hotspot, with seven individuals harbouring a c.1706G>A (p.Arg569His) variant, and one child harbouring a c.1531T>C (p.Tyr511His) variant. Literature review yielded a total of 46 patients from 20 papers. Data analysis showed that short stature, hypoparathyroidism and hypocalcemia, ocular and dental defects, skeletal features including cortical thickening and medullary stenosis of tubular bones, and seizures/spasms were present in more than 70% of the reported KCS2 cases. Conclusion We provide detailed characteristics of the largest KCS2 group in China and present the first genetically confirmed instance of father‐to‐daughter transmission of KCS2. Our study confirms that Arg569His is the hot spot variant and summarizes the typical phenotypes of KCS2, which would help early diagnosis and intervention. We provided detailed characteristics of eight individuals with genetically confirmed KCS2, which has been the largest cohort of KCS2 so far in China. We present the first genetically confirmed instance of father‐to‐daughter transmission of KCS2, which demonstrates an equal sex ratio of affected individuals.

Osteocraniostenosis (OCS, OMIM #602361) is a severe, usually lethal condition characterized by gracile bones with thin diaphyses, a cloverleaf-shaped skull and splenic hypo/aplasia. The condition is caused by heterozygous mutations in the FAM111A gene and is allelic to the non-lethal, dominant disorder Kenny-Caffey syndrome (KCS, OMIM #127000). Here we report two new cases of OCS, including one with a detailed pathological examination. We review the main diagnostic signs of OCS both before and after birth based on our observations and on the literature. We then review the current knowledge on the mutational spectrum of FAM111A associated with either OCS or KCS, including three novel variants, both from one of the OCS fetuses described here, and from further cases diagnosed at our centers. This report refines the previous knowledge on OCS and expands the mutational spectrum that results in either OCS or KCS.

In 2018, data from a surveillance study in Botswana evaluating adverse birth outcomes raised concerns that women on antiretroviral therapy (ART) containing dolutegravir (DTG) may be at increased risk for neural tube defects (NTDs). The mechanism of action for DTG involves chelation of Mg 2+ ions in the active site of the viral integrase. Plasma Mg 2+ homeostasis is maintained primarily through dietary intake and reabsorption in the kidneys. Inadequate dietary Mg 2+ intake over several months results in slow depletion of plasma Mg 2+ and chronic latent hypomagnesemia, a condition prevalent in women of reproductive age worldwide. Mg 2+ is critical for normal embryonic development and neural tube closure. We hypothesized that DTG therapy might slowly deplete plasma Mg 2+ and reduce the amount available to the embryo, and that mice with pre-existing hypomagnesemia due to genetic variation and/or dietary Mg 2+ insufficiency at the time of conception and initiation of DTG treatment would be at increased risk for NTDs. We used two different approaches to test our hypothesis: 1) we selected mouse strains that had inherently different basal plasma Mg 2+ levels and 2) placed mice on diets with different concentrations of Mg 2+ . Plasma and urine Mg 2+ were determined prior to timed mating. Pregnant mice were treated daily with vehicle or DTG beginning on the day of conception and embryos examined for NTDs on gestational day 9.5. Plasma DTG was measured for pharmacokinetic analysis. Our results demonstrate that hypomagnesemia prior to conception, due to genetic variation and/or insufficient dietary Mg 2+ intake, increases the risk for NTDs in mice exposed to DTG. We also analyzed whole-exome sequencing data from inbred mouse strains and identified 9 predicted deleterious missense variants in Fam111a that were unique to the LM/Bc strain. Human FAM111A variants are associated with hypomagnesemia and renal Mg 2+ wasting. The LM/Bc strain exhibits this same phenotype and was the strain most susceptible to DTG-NTDs. Our results suggest that monitoring plasma Mg 2+ levels in patients on ART regimens that include DTG, identifying other risk factors that impact Mg 2+ homeostasis, and correcting deficiencies in this micronutrient might provide an effective strategy for mitigating NTD risk.