Human FAM111A inhibits vaccinia virus replication by degrading viral protein I3 and is antagonized by poxvirus host range factor SPI-1.

Zoonotic poxviruses such as mpox virus (MPXV) continue to threaten public health safety since the eradication of smallpox. Vaccinia virus (VACV), the prototypic poxvirus used as the vaccine strain for smallpox eradication, is the best-characterized member of the poxvirus family. VACV encodes a serine protease inhibitor 1 (SPI-1) conserved in all orthopoxviruses, which has been recognized as a host range factor for modified VACV Ankara (MVA), an approved smallpox vaccine and a promising vaccine vector. FAM111A (family with sequence similarity 111 member A), a nuclear protein that regulates host DNA replication, was shown to restrict the replication of a VACV SPI-1 deletion mutant (VACV-ΔSPI-1) in human cells. Nevertheless, the detailed antiviral mechanisms of FAM111A were unresolved. Here, we show that FAM111A is a potent restriction factor for VACV-ΔSPI-1 and MVA. Deletion of FAM111A rescued the replication of MVA and VACV-ΔSPI-1 and overexpression of FAM111A significantly reduced viral DNA replication and virus titers but did not affect viral early gene expression. The antiviral effect of FAM111A necessitated its trypsin-like protease domain and DNA-binding domain but not the PCNA-interacting motif. We further identified that FAM111A translocated into the cytoplasm upon VACV infection by degrading the nuclear pore complex via its protease activity, interacted with VACV DNA-binding protein I3, and promoted I3 degradation through autophagy. Moreover, SPI-1 from VACV, MPXV, or lumpy skin disease virus was able to antagonize FAM111A by prohibiting its nuclear export. Our findings reveal the detailed mechanism by which FAM111A inhibits VACV and provide explanations for the immune evasive function of VACV SPI-1.

Unravelling the Intricate Roles of FAM111A and FAM111B: From Protease-Mediated Cellular Processes to Disease Implications.

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.

FAM111A induces nuclear dysfunction in disease and viral restriction.

Mutations in the nuclear trypsin-like serine protease FAM111A cause Kenny-Caffey syndrome (KCS2) with hypoparathyroidism and skeletal dysplasia or perinatally lethal osteocraniostenosis (OCS). In addition, FAM111A was identified as a restriction factor for certain host range mutants of the SV40 polyomavirus and VACV orthopoxvirus. However, because FAM111A function is poorly characterized, its roles in restricting viral replication and the etiology of KCS2 and OCS remain undefined. We find that FAM111A KCS2 and OCS patient mutants are hyperactive and cytotoxic, inducing apoptosis-like phenotypes such as disruption of nuclear structure and pore distribution, in a protease-dependent manner. Moreover, wild-type FAM111A activity causes similar nuclear phenotypes, including the loss of nuclear barrier function, when SV40 host range mutants attempt to replicate in restrictive cells. Interestingly, pan-caspase inhibitors do not block these FAM111A-induced phenotypes, implying it acts independently or upstream of caspases. In this regard, we identify nucleoporins and the associated GANP transcription/replication factor as FAM111A interactors and candidate targets. Overall, we reveal a potentially unifying mechanism through which deregulated FAM111A activity restricts viral replication and causes KCS2 and OCS.

Adult Chinese twins with Kenny-Caffey syndrome type 2: A potential age-dependent phenotype and review of literature.

Kenny-Caffey syndrome (KCS) type 2 (OMIM 127000) is a rare syndromic cause of hypoparathyroidism which is characterized by proportionate short stature, long bone abnormalities, delayed closure of anterior fontanelle, eye abnormalities, and normal intelligence. It is caused by variants in FAM111A (NM_001942519.1). In this review, we reported the first Chinese patients, a pair of monozygotic twins, with genetically confirmed KCS type 2 with over 20 years follow-up. We summarized the clinical features of 14 previously reported and genetically confirmed KCS type 2 patients; our twin patients exhibited a unique spinal manifestation which could be an important age-dependent feature of KCS type 2. In this review, over 60% KCS type 2 patients had dental problem and over 80% suffered from refractive errors or structural eye abnormalities. Therefore, early dental, ophthalmological, and orthopedic assessments are warranted for KCS type 2 patients. Micro-orchidism, previously reported in KCS type 2 patients, was also detected in our patients. The possibility of subfertility should be considered in male KCS type 2 patients. A multidisciplinary management approach for this rare syndrome is recommended.

Report of a novel variant in the FAM111A gene in a fetus with multiple anomalies including gracile bones, hypoplastic spleen, and hypomineralized skull.

Kenny-Caffey syndrome type 2 (KCS2) and osteocraniostenosis (OCS) are allelic disorders caused by heterozygous pathogenic variants in the FAM111A gene. Both conditions are characterized by gracile bones, characteristic facial features, hypomineralized skull with delayed closure of fontanelles and hypoparathyroidism. OCS and KCS2 are often referred to as FAM111A-related syndromes as a group; although OCS presents with a more severe, perinatal lethal phenotype. We report a novel FAM111A mutation in a fetus with poorly ossified skull, proportionate long extremities with thin diaphysis, and hypoplastic spleen consistent with FAM111A-related syndromes. Trio whole exome sequencing identified a p.Y562S de novo missense variant in the FAM111A gene. The variant shows significant similarity to other reported pathogenic mutations fitting proposed pathophysiologic mechanism which provide sufficient evidence for classification as likely pathogenic. Our report contributed a novel variant to the handful of OCS and KCS2 cases reported with pathogenic variants.

IRF2 inhibits ZIKV replication by promoting FAM111A expression to enhance the host restriction effect of RFC3.

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.

Overlapping phenotype comprising Kenny-Caffey type 2 and Sanjad-Sakati syndromes: The first case report.

Kenny-Caffey syndrome (KCS) is a rare hereditary skeletal disorder involving hypoparathyroidism. The autosomal dominant form (KCS2), caused by heterozygous pathogenic variants in the FAM111A gene, is distinguished from the autosomal recessive form (KCS1) and Sanjad-Sakati syndrome (SSS), both caused by pathogenic variants in the tubulin folding cofactor E (TBCE) gene, by the absence of microcephaly and intellectual disability. We present a patient with KCS2 caused by a de novo pathogenic variant c.1706G>A (p.Arg569His) in FAM111A gene, presenting intellectual disability and microcephaly, which are considered to be typical signs of SSS. We suggest that KCS1, KCS2, and SSS may not represent mutually exclusive clinical entities, but possibly an overlapping spectrum.

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.

Further delineation of phenotype and genotype of Kenny-Caffey syndrome type 2 (phenotype and genotype of KCS type 2).

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.

Compound Heterozygous Variants in FAM111A Cause Autosomal Recessive Kenny-Caffey Syndrome Type 2

Kenny-Caffey syndrome (KCS) is a rare autosomal recessive (AR)/dominant disease characterized by hypoparathyroidism, skeletal dysplasia, dwarfism, and dysmorphism. FAM111A 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 FAM111A gene mutation. The FAM111A 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 FAM111A 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 FAM111A mutation in Turkey. The phenotype of the patient is compatible with OCS, and the detected variants may explain the disease genetically.

Gene-nutrient interactions that impact magnesium homeostasis increase risk for neural tube defects in mice exposed to dolutegravir.

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 Mg2+ ions in the active site of the viral integrase. Plasma Mg2+ homeostasis is maintained primarily through dietary intake and reabsorption in the kidneys. Inadequate dietary Mg2+ intake over several months results in slow depletion of plasma Mg2+ and chronic latent hypomagnesemia, a condition prevalent in women of reproductive age worldwide. Mg2+ is critical for normal embryonic development and neural tube closure. We hypothesized that DTG therapy might slowly deplete plasma Mg2+ and reduce the amount available to the embryo, and that mice with pre-existing hypomagnesemia due to genetic variation and/or dietary Mg2+ 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 Mg2+ levels and 2) placed mice on diets with different concentrations of Mg2+. Plasma and urine Mg2+ 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 Mg2+ 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 Mg2+ wasting. The LM/Bc strain exhibits this same phenotype and was the strain most susceptible to DTG-NTDs. Our results suggest that monitoring plasma Mg2+ levels in patients on ART regimens that include DTG, identifying other risk factors that impact Mg2+ homeostasis, and correcting deficiencies in this micronutrient might provide an effective strategy for mitigating NTD risk.

Clinical and genetic features of Kenny-Caffey syndrome type 2 with multiple electrolyte disturbances: A case report.

BACKGROUND: Hypoparathyroidism, which can be sporadic or a component of an inherited syndrome, is the most common cause of hypocalcemia. If hypocalcemia is accompanied by other electrolyte disturbances, such as hypokalemia and hypomagnesemia, then the cause, such as renal tubular disease, should be carefully identified. CASE SUMMARY: An 18-year-old female visited our clinic because of short stature and facial deformities, including typical phenotypes, such as low ear position, depression of the nasal bridge, small hands and feet, and loss of dentition. The lab results suggested normal parathyroid hormone but hypocalcemia. In addition, multiple electrolyte disturbances were found, including hypokalemia, hypocalcemia and hypomagnesemia. The physical signs showed a short fourth metatarsal bone of both feet. The X-ray images showed cortical thickening of long bones and narrowing of the medulla of the lumen. Cranial computed tomography indicated calcification in the bilateral basal ganglia. Finally, the genetic investigation showed a de novo heterogenous mutation of "FAM111A" (c. G1706A:p.R569H). Through a review of previously reported cases, the mutation was found to be the most common mutation site in Kenny-Caffey syndrome type 2 (KCS2) cases reported thus far (16/23, 69.6%). The mutation was slightly more prevalent in females than in males (11/16, 68.8%). Except for hypocalcemia, other clinical manifestations are heterogeneous. CONCLUSION: As a rare autosomal dominant genetic disease of hypoparathyroidism, the clinical manifestations of KCS2 are atypical and diverse. This girl presented with short stature, facial deformities and skeletal deformities. The laboratory results revealed hypocalcemia as the main electrolyte disturbance. Even though her family members showed normal phenotypes, gene detection was performed to find the mutation of the FAM111A gene and confirmed the diagnosis of KCS2.

FAM111A Is a Novel Molecular Marker for Oocyte Aging.

Aging is the main cause of decline in oocyte quality, which can further trigger the failure of assisted reproductive technology (ART). Exploring age-related genes in oocytes is an important way to investigate the molecular mechanisms involved in oocyte aging. To provide novel insight into this field, we performed a pooled analysis of publicly available datasets, using the overlapping results of two statistical methods on two Gene Expression Omnibus (GEO) datasets. The methods utilized in the current study mainly include Spearman rank correlation, the Wilcoxon signed-rank test, t-tests, Venn diagrams, Gene Ontology (GO), Protein-Protein Interaction (PPI), Gene Set Enrichment Analysis (GSEA), Gene Set Variation Analysis (GSVA), and receiver operating characteristic (ROC) curve analysis. We identified hundreds of age-related genes across different gene expression datasets of in vitro maturation-metaphase II (IVM-MII) oocytes. Age-related genes in IVM-MII oocytes were involved in the biological processes of cellular metabolism, DNA replication, and histone modifications. Among these age-related genes, FAM111A expression presented a robust correlation with age, seen in the results of different statistical methods and different datasets. FAM111A is associated with the processes of chromosome segregation and cell cycle regulation. Thus, this enzyme is potentially an interesting novel marker for the aging of oocytes, and warrants further mechanistic study.

Case report: Late middle-aged features of FAM111A variant, Kenny-Caffey syndrome type 2-suggestive symptoms during a long follow-up.

Kenny-Caffey syndrome type 2 (KCS2) is an extremely rare skeletal disorder involving hypoparathyroidism and short stature. It has an autosomal dominant pattern of inheritance and is caused by variants in the FAM111 trypsin-like peptidase A (FAM111A) gene. This disease is often difficult to diagnose due to a wide range of more common diseases manifesting hypoparathyroidism and short stature. Herein, we present the case of a 56-year-old female patient with idiopathic hypoparathyroidism and a short stature. The patient was treated for these conditions during childhood. Upon re-evaluating the etiology of KCS2, we suspected that the patient had the disorder because of clinical manifestations, such as cortical thickening and medullary stenosis of the bones, and lack of intellectual abnormalities. Genetic testing identified a heterozygous missense variant in the FAM111A gene (p.R569H). Interestingly, the patient also had bilateral sensorineural hearing loss and vestibular dysfunction, which have been rarely described in previous reports of pediatric cases. In KCS2, inner ear dysfunction due to Eustachian tube dysfunction may progress in middle age or later. However, this disease is now being reported in younger patients. Nevertheless, our case may be instructive of how such cases emerge chronically after middle age. Herein, we also provide a literature review of KCS2.

Clinical and Molecular Diagnosis of Osteocraniostenosis in Fetuses and Newborns: Prenatal Ultrasound, Clinical, Radiological and Pathological Features.

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.

Functions and evolution of FAM111 serine proteases.

Proteolysis plays fundamental and regulatory roles in diverse cellular processes. The serine protease FAM111A (FAM111 trypsin-like peptidase A) emerged recently as a protease involved in two seemingly distinct processes: DNA replication and antiviral defense. FAM111A localizes to nascent DNA and plays a role at the DNA replication fork. At the fork, FAM111A is hypothesized to promote DNA replication at DNA-protein crosslinks (DPCs) and protein obstacles. On the other hand, FAM111A has also been identified as a host restriction factor for mutants of SV40 and orthopoxviruses. FAM111A also has a paralog, FAM111B, a serine protease with unknown cellular functions. Furthermore, heterozygous missense mutations in FAM111A and FAM111B cause distinct genetic disorders. In this review, we discuss possible models that could explain how FAM111A can function as a protease in both DNA replication and antiviral defense. We also review the consequences of FAM111A and FAM111B mutations and explore possible mechanisms underlying the diseases. Additionally, we propose a possible explanation for what drove the evolution of FAM111 proteins and discuss why some species have two FAM111 proteases. Altogether, studies of FAM111 proteases in DNA repair, antiviral defense, and genetic diseases will help us elucidate their functions and the regulatory mechanisms.

Genotype-phenotype spectrum in isolated and syndromic nanophthalmos.

PURPOSE: To (i) describe a series of patients with isolated or syndromic nanophthalmos with the underlying genetic causes, including novel pathogenic variants and their functional characterization and (ii) to study the association of retinal dystrophy in patients with MFRP variants, based on a detailed literature review of genotype-phenotype correlations. METHODS: Patients with nanophthalmos and available family members received a comprehensive ophthalmological examination. Genetic analysis was based on whole-exome sequencing and variant calling in core genes including MFRP, BEST1, TMEM98, PRSS56, CRB1, GJA1, C1QTNF5, MYRF and FAM111A. A minigene assay was performed for functional characterization of a splice site variant. RESULTS: Seven patients, aged between three and 65 years, from five unrelated families were included. Novel pathogenic variants in MFRP (c.497C>T, c.899-3C>A, c.1180G>A), and PRSS56 (c.1202C>A), and a recurrent de novo variant in FAM111A (c.1706G>A) in a patient with Kenny-Caffey syndrome type 2, were identified. In addition, we report co-inheritance of MFRP-related nanophthalmos and ADAR-related Aicardi-Goutières syndrome. CONCLUSION: Nanophthalmos is a genetically heterogeneous condition, and the severity of ocular manifestations appears not to correlate with variants in a specific gene. However, retinal dystrophy is only observed in patients harbouring pathogenic MFRP variants. Furthermore, heterozygous carriers of MFRP and PRSS56 should be screened for the presence of high hyperopia. Identifying nanophthalmos as an isolated condition or as part of a syndrome has implications for counselling and can accelerate the interdisciplinary care of patients.

The role of calcium-sensing receptor signaling in regulating transepithelial calcium transport.

The calcium-sensing receptor (CaSR) plays a critical role in sensing extracellular calcium (Ca2+) and signaling to maintain Ca2+ homeostasis. In the parathyroid, the CaSR regulates secretion of parathyroid hormone, which functions to increase extracellular Ca2+ levels. The CaSR is also located in other organs imperative to Ca2+ homeostasis including the kidney and intestine, where it modulates Ca2+ reabsorption and absorption, respectively. In this review, we describe CaSR expression and its function in transepithelial Ca2+ transport in the kidney and intestine. Activation of the CaSR leads to G protein dependent and independent signaling cascades. The known CaSR signal transduction pathways involved in modulating paracellular and transcellular epithelial Ca2+ transport are discussed. Mutations in the CaSR cause a range of diseases that manifest in altered serum Ca2+ levels. Gain-of-function mutations in the CaSR result in autosomal dominant hypocalcemia type 1, while loss-of-function mutations cause familial hypocalciuric hypercalcemia. Additionally, the putative serine protease, FAM111A, is discussed as a potential regulator of the CaSR because mutations in FAM111A cause Kenny Caffey syndrome type 2, gracile bone dysplasia, and osteocraniostenosis, diseases that are characterized by hypocalcemia, hypoparathyroidism, and bony abnormalities, i.e. share phenotypic features of autosomal dominant hypocalcemia. Recent work has helped to elucidate the effect of CaSR signaling cascades on downstream proteins involved in Ca2+ transport across renal and intestinal epithelia; however, much remains to be discovered.

Short stature and hypoparathyroidism in a child with Kenny-Caffey syndrome type 2 due to a novel mutation in FAM111A gene.

BACKGROUND: Hypoparathyroidism in children is a heterogeneous group with diverse genetic etiologies. To aid clinicians in the investigation and management of children with hypoparathyroidism, we describe the phenotype of a 6-year-old child with hypoparathyroidism and short stature diagnosed with Kenny-Caffey syndrome (KCS) Type 2 and the subsequent response to growth hormone (GH) treatment. CASE PRESENTATION: The proband presented in the neonatal period with hypocalcemic seizures secondary to hypoparathyroidism. Her phenotype included small hands and feet, hypoplastic and dystrophic nails, hypoplastic mid-face and macrocrania. Postnatal growth was delayed but neurodevelopment was normal. A skeletal survey at 2 years of age was suggestive of KCS Type 2 and genetic testing revealed a novel de novo heterozygous mutation c.1622C > A (p.Ser541Tyr) in FAM111A. At 3 years and 2 months, her height was 80cms (SDS -3.86). She had normal overnight GH levels. GH therapy was commenced at a dose of 4.9 mg/m2/week for her short stature and low height velocity of 5cms/year. At the end of the first and second years of GH treatment, height velocity was 6.5cms/year and 7.2cms/year, respectively with maximal dose of 7.24 mg/m2/week. CONCLUSION: This case highlights the phenotype and the limited response to GH in a child with genetically proven KCS type 2. Long-term registries monitoring growth outcomes following GH therapy in patients with rare genetic conditions may help guide clinical decisions regarding the use and doses of GH in these conditions.