Report of a case of Raine syndrome and literature review

Potential Role of Protein Kinase FAM20C on the Brain in Raine Syndrome, an In Silico Analysis

FAM20C (family with sequence similarity 20, member C) is a serine/threonine-specific protein kinase that is ubiquitously expressed and mainly associated with biomineralization and phosphatemia regulation. It is mostly known due to pathogenic variants causing its deficiency, which results in Raine syndrome (RNS), a sclerosing bone dysplasia with hypophosphatemia. The phenotype is recognized by the skeletal features, which are related to hypophosphorylation of different FAM20C bone-target proteins. However, FAM20C has many targets, including brain proteins and the cerebrospinal fluid phosphoproteome. Individuals with RNS can have developmental delay, intellectual disability, seizures, and structural brain defects, but little is known about FAM20C brain-target-protein dysregulation or about a potential pathogenesis associated with neurologic features. In order to identify the potential FAM20C actions on the brain, an in silico analysis was conducted. Structural and functional defects reported in RNS were described; FAM20C targets and interactors were identified, including their brain expression. Gene ontology of molecular processes, function, and components was completed for these targets, as well as for potential involved signaling pathways and diseases. The BioGRID and Human Protein Atlas databases, the Gorilla tool, and the PANTHER and DisGeNET databases were used. Results show that genes with high expression in the brain are involved in cholesterol and lipoprotein processes, plus axo-dendritic transport and the neuron part. These results could highlight some proteins involved in the neurologic pathogenesis of RNS.

Hereditary Rickets: A Quick Guide for the Pediatrician

With the increased discovery of genes implicated in vitamin D metabolism and the regulation of calcium and phosphate homeostasis, a growing number of genetic forms of rickets are now recognized. These are categorized into calciopenic and phosphopenic rickets. Calciopenic forms of hereditary rickets are caused by genetic mutations that alter the enzymatic activity in the vitamin D activation pathway or impair the vitamin D receptor action. Hereditary forms of phosphopenic rickets, on the other hand, are caused by genetic mutations that lead to increased expression of FGF23 hormone or that impair the absorptive capacity of phosphate at the proximal renal tubule. Due to the clinical overlap between acquired and genetic forms of rickets, identifying children with hereditary rickets can be challenging. A clear understanding of the molecular basis of hereditary forms of rickets and their associated biochemical patterns allow the health care provider to assign the correct diagnosis, avoid non-effective interventions and shorten the duration of the diagnostic journey in these children. In this mini-review, known forms of hereditary rickets listed on the Online Mendelian Inheritance in Man database are discussed. Further, a clinical approach to identify and diagnose children with hereditary forms of rickets is suggested.

Quantification of FAM20A in human milk and identification of calcium metabolism proteins

BACKGROUND

FAM20A, a recently discovered protein, is thought to have a fundamental role in inhibiting ectopic calcification. Several studies have demonstrated that variants of FAM20A are causative for the rare autosomal recessive disorder, enamel-renal syndrome (ERS). ERS is characterized by defective mineralization of dental enamel and nephrocalcinosis suggesting that FAM20A is an extracellular matrix protein, dysfunction of which causes calcification of the secretory epithelial tissues. FAM20A is a low-abundant protein that is difficult to detect in biofluids such as blood, saliva, and urine. Thus, we speculated the abundance of FAM20A to be high in human milk, since the secretory epithelium of lactating mammary tissue is involved in the secretion of highly concentrated calcium. Therefore, the primary aim of this research is to describe the processes/methodology taken to quantify FAM20A in human milk and identify other proteins involved in calcium metabolism.

METHOD

This study used mass spectrometry-driven quantitative proteomics: (1) to quantify FAM20A in human milk of three women and (2) to identify proteins associated with calcium regulation by bioinformatic analyses on whole and milk fat globule membrane fractions.

RESULTS

Shotgun MS/MS driven proteomics identified FAM20A in whole milk, and subsequent analysis using targeted proteomics also successfully quantified FAM20A in all samples. Combination of sample preparation, fractionation, and LC-MS/MS proteomics analysis generated 136 proteins previously undiscovered in human milk; 21 of these appear to be associated with calcium metabolism.

CONCLUSION

Using mass spectrometry-driven proteomics, we successfully quantified FAM20A from transitional to mature milk and obtained a list of proteins involved in calcium metabolism. Furthermore, we show the value of using a combination of both shotgun and targeted driven proteomics for the identification of this low abundant protein in human milk.

FAM20C Overview: Classic and Novel Targets, Pathogenic Variants and Raine Syndrome Phenotypes

FAM20C is a gene coding for a protein kinase that targets S-X-E/pS motifs on different phosphoproteins belonging to diverse tissues. Pathogenic variants of FAM20C are responsible for Raine syndrome (RS), initially described as a lethal and congenital osteosclerotic dysplasia characterized by generalized atherosclerosis with periosteal bone formation, characteristic facial dysmorphisms and intracerebral calcifications. The aim of this review is to give an overview of targets and variants of FAM20C as well as RS aspects. We performed a wide phenotypic review focusing on clinical aspects and differences between all lethal (LRS) and non-lethal (NLRS) reported cases, besides the FAM20C pathogenic variant description for each. As new targets of FAM20C kinase have been identified, we reviewed FAM20C targets and their functions in bone and other tissues, with emphasis on novel targets not previously considered. We found the classic lethal and milder non-lethal phenotypes. The milder phenotype is defined by a large spectrum ranging from osteonecrosis to osteosclerosis with additional congenital defects or intellectual disability in some cases. We discuss our current understanding of FAM20C deficiency, its mechanism in RS through classic FAM20C targets in bone tissue and its potential biological relevance through novel targets in non-bone tissues.

Non-lethal Raine Syndrome Report Lacking Characteristic Clinical Features

Raine syndrome is a rare, often lethal autosomal recessive condition marked by congenital malformations that range in severity. Considering that several case reports of this syndrome describe cases of stillbirth or perinatal death, information about the clinical presentation and development of this condition in mild, non-lethal cases is lacking. With that in mind, in this case report, we describe the clinical, oro-dental, and skeletal findings of a 14-year-old Brazilian patient diagnosed with a mild form of non-lethal Raine syndrome. This patient has very mild facial dysmorphia, not displaying hypoplastic nose, micrognathia, low set ears or depressed nasal bridge, which is uncommon even in other mild, non-lethal cases of RS. Furthermore, this patient has bilateral brain calcifications and a series of oro-dental abnormalities, such as amelogenesis imperfecta and recurrent periodontal abcesses. Sanger sequencing of genomic DNA identified a homozygous missense variant c.1487C > T at exon 9 of FAM20C (NM_020223.4) in the patient. The patient's mother carries the same variant but is heterozygous. This variant predicts a proline to leucine substitution in position 496 (p.P496L, NP_064608.2) previously reported, which allows for the phenotypic comparison between these cases. This way, this case report calls attention to how differently RS can appear, highlighting the importance of new non-lethal Raine syndrome case reports to help further determine the phenotypic spectrum of this condition.

The ABCs of the atypical Fam20 secretory pathway kinases

The study of extracellular phosphorylation was initiated in late 19th century when the secreted milk protein, casein, and egg-yolk protein, phosvitin, were shown to be phosphorylated. However, it took more than a century to identify Fam20C, which phosphorylates both casein and phosvitin under physiological conditions. This kinase, along with its family members Fam20A and Fam20B, defined a new family with altered amino acid sequences highly atypical from the canonical 540 kinases comprising the kinome. Fam20B is a glycan kinase that phosphorylates xylose residues and triggers peptidoglycan biosynthesis, a role conserved from sponges to human. The protein kinase, Fam20C, conserved from nematodes to humans, phosphorylates well over 100 substrates in the secretory pathway with overall functions postulated to encompass endoplasmic reticulum homeostasis, nutrition, cardiac function, coagulation, and biomineralization. The preferred phosphorylation motif of Fam20C is SxE/pS, and structural studies revealed that related member Fam20A allosterically activates Fam20C by forming a heterodimeric/tetrameric complex. Fam20A, a pseudokinase, is observed only in vertebrates. Loss-of-function genetic alterations in the Fam20 family lead to human diseases such as amelogenesis imperfecta, nephrocalcinosis, lethal and nonlethal forms of Raine syndrome with major skeletal defects, and altered phosphate homeostasis. Together, these three members of the Fam20 family modulate a diverse network of secretory pathway components playing crucial roles in health and disease. The overarching theme of this review is to highlight the progress that has been made in the emerging field of extracellular phosphorylation and the key roles secretory pathway kinases play in an ever-expanding number of cellular processes.

Prognostic and immunological role of Fam20C in pan-cancer

Background: The family with sequence similarity 20-member C (Fam20C) kinase plays important roles in physiopathological process and is responsible for majority of the secreted phosphoproteome, including substrates associated with tumor cell migration. However, it remains unclear whether Fam20C plays a role in cancers. Here, we aimed to analyze the expression and prognostic value of Fam20C in pan-cancer and to gain insights into the association between Fam20C and immune infiltration.

Methods: We analyzed Fam20C expression patterns and the associations between Fam20C expression levels and prognosis in pan-cancer via the ONCOMINE, TIMER (Tumor Immune Estimation Resource), PrognoScan, GEPIA (Gene Expression Profiling Interactive Analysis), and Kaplan–Meier Plotter databases. After that, GEPIA and TIMER databases were applied to investigate the relations between Fam20C expression and immune infiltration across different cancer types, especially BLCA (bladder urothelial carcinoma), LGG (brain lower grade glioma), and STAD (stomach adenocarcinoma).

Results: Compared with adjacent normal tissues, Fam20C was widely expressed across many cancers. In general, Fam20C showed a detrimental role in pan-cancer, it was positively associated with poor survival of BLCA, LGG, and STAD patients. Specifically, based on TCGA (The Cancer Genome Atlas) database, a high expression level of Fam20C was associated with worse prognostic value in stages T2–T4 and stages N0–N2 in the cohort of STAD patients. Moreover, Fam20C expression had positive associations with immune infiltration, including CD4⁺ T cells, macrophages, neutrophils, and dendritic cells, and other diverse immune cells in BLCA, LGG, and STAD.

Conclusion: Fam20C may serve as a promising prognostic biomarker in pan-cancer and has positive associations with immune infiltrates.

Transcription Factors of the Alx Family: Evolutionarily Conserved Regulators of Deuterostome Skeletogenesis

Members of the alx gene family encode transcription factors that contain a highly conserved Paired-class, DNA-binding homeodomain, and a C-terminal OAR/Aristaless domain. Phylogenetic and comparative genomic studies have revealed complex patterns of alx gene duplications during deuterostome evolution. Remarkably, alx genes have been implicated in skeletogenesis in both echinoderms and vertebrates. In this review, we provide an overview of current knowledge concerning alx genes in deuterostomes. We highlight their evolutionarily conserved role in skeletogenesis and draw parallels and distinctions between the skeletogenic gene regulatory circuitries of diverse groups within the superphylum.

Raine syndrome: Prenatal diagnosis based on recognizable fetal facial features and characteristic intracranial calcification

OBJECTIVE

The purpose of this study was to elucidate the facial morphology and the pattern of internal malformations in three fetuses with RS born to first cousins of Egyptian decent.

METHODS

The fetal ultrasonography findings were highly suggestive of RS leading to targeted Sanger sequencing of FAM20C and postnatal assessment.

RESULTS

The prenatal ultrasound findings of osteosclerotic skull, exorbitism, hypoplastic nose, midface hypoplasia, small mouth with down-curved corners, and a distinct and recognizable pattern of intracranial calcification were identified in three fetuses with RS. The calcifications were evident specifically around the corpus callosum and/or ventricular walls. Ectopic renal and hepatic calcifications, pulmonary hypoplasia, mild rhizomelic shortening of the upper limbs, intrauterine fractures, and cerebellar hypoplasia were also noted. Molecular analysis identified three novel homozygous variants, two frameshift: [c.456delC (p.Gly153Alafs*34)] in exon 1 and [c.905delT (Phe302Serfs*35)] in exon 4 and one nonsense mutation in exon 10, [c.1557C>G(p.Tyrs519*)]. The three variants were segregated with the phenotype. This is the first description of a phenotype associated with homozygous truncating variants of FAM20C.

CONCLUSION

RS has characteristic prenatal ultrasound findings which can improve the prenatal identification of this condition and help in guiding the molecular diagnosis and counseling.

A Rare Cause of Hypophosphatemia: Raine Syndrome Changing Clinical Features with Age

Raine Syndrome (RS) is caused by biallelic loss-of-function mutations in FAM20C gene and characterized by hypophosphatemia, typical facial and skeletal features. Subperiosteal bone formation and generalized osteosclerosis are the most common radiological findings. Here we present a new case with RS. A 9-month-old male patient on a home-type ventilator was referred for hypophosphatemia. He was born with a weight of 3800 g to non-consanguineous parents. Prenatal ultrasound had demonstrated nasal bone agenesis. A large anterior fontanel, frontal bossing, exophthalmos, hypoplastic nose, high arched palate, low set ears, triangular mouth, and corneal opacification were detected on physical examination. Serial skeletal X-rays revealed diffuse osteosclerosis at birth which was gradually decreased by the age of 5 months with subperiosteal undermineralized bone formation and medullary space of long bone could be distinguishable with bone-within-a-bone appearance. At 9 months of age, hand X-ray revealed cupping of the ulna with loose radial bone margin with minimal fraying and osteopenia. Cranial computed tomography scan showed bilateral periventricular calcification and hydrocephalus in progress. The clinical, laboratory, and radiological examinations were consistent with RS. Molecular analyses revealed a compound heterozygous mutation in FAM20C gene (a known pathogenic mutation, c.1645C > T, p.Arg549Trp; and a novel c.863 + 5 G > C variant). The patient died due to respiratory failure at 17 months of age. This case allowed us to demonstrate natural progression of skeletal features in RS. Furthermore, we have described a novel FAM20C variant causing RS. Previous literature on RS is also reviewed.

Two Novel FAM20C Variants in A Family with Raine Syndrome

Two siblings from a Mexican family who carried lethal Raine syndrome are presented. A newborn term male (case 1) and his 21 gestational week brother (case 2), with a similar osteosclerotic pattern: generalized osteosclerosis, which is more evident in facial bones and cranial base. Prenatal findings at 21 weeks and histopathological features for case 2 are described. A novel combination of biallelic FAM20C pathogenic variants were detected, a maternal cytosine duplication at position 456 and a paternal deletion of a cytosine in position 474 in exon 1, which change the reading frame with a premature termination at codon 207 and 185 respectively. These changes are in concordance with a negative detection of the protein in liver and kidney as shown in case 2. Necropsy showed absence of pancreatic Langerhans Islets, which are reported here for the first time. Corpus callosum absence is added to the few reported cases of brain defects in Raine syndrome. This report shows two new FAM20C variants not described previously, and negative protein detection in the liver and the kidney. We highlight that lethal Raine syndrome is well defined as early as 21 weeks, including mineralization defects and craniofacial features. Pancreas and brain defects found here in FAM20C deficiency extend the functional spectrum of this protein to previously unknown organs.

A novel FAM20C mutation causes a rare form of neonatal lethal Raine syndrome

Raine syndrome is a rare, autosomal recessive, osteosclerotic bone dysplasia due to pathogenic variants in FAM20C. The clinical phenotype is characterized by generalized osteosclerosis affecting all bones, cerebral calcifications, and craniofacial dysmorphism. Most cases present during the neonatal period with early lethality due to pulmonary hypoplasia and respiratory compromise while only few affected individuals have been reported to survive into adulthood. FAM20C is a ubiquitously expressed protein kinase that contains five functional domains including a catalytic domain, a binding pocket for FAM20A and three distinct N-glycosylation sites. We report a newborn infant with a history of prenatal onset fractures, generalized osteosclerosis, and craniofacial dysmorphism and early lethality. The clinical presentation was highly suggestive of Raine syndrome. A homozygous, novel missense variant in exon 5 of FAM20C (c.1007T>G; p.Met336Arg) was identified by targeted Sanger sequencing. Following in silico analysis and mapping of the variant on a three-dimensional (3D) model of FAM20C it is predicted to be deleterious and to affect N-glycosylation, protein folding, and subsequent secretion of FAM20C. In addition, we reviewed all published FAM20C mutations and observed that most pathogenic variants affect functional regions within the protein establishing evidence for an emerging genotype-phenotype correlation.

Loss of Fam20c causes defects in the acinar and duct structure of salivary glands in mice

Family with sequence similarity 20-member C (FAM20C), a recently characterized Golgi kinase, performs numerous biological functions by phosphorylating more than 100 secreted proteins. However, the role of FAM20C in the salivary glands remains undefined. The present study demonstrated that FAM20C is mainly located in the cytoplasm of duct epithelial cells in the salivary glands. Fam20c^f/f; Mmtv-Cre mice were created in which Fam20c was inactivated in the salivary gland cells and observed that the number of ducts and the ductal cross-sectional area increased significantly, while the number of acinar cells was reduced. The granular convoluted tubules (GCTs) exhibited an accumulation of aberrant secretory granules, along with a reduced expression and altered distribution patterns of β nerve growth factor, α-amylase and bone morphogenetic protein (BMP) 4. This abnormality suggested that the GCT cells were immature and exhibited defects in developmental and secretory functions. In accordance with the morphological alterations and the reduced number of acinar cells, FAM20C deficiency in the salivary glands significantly decreased the salivary flow rate. The Na⁺, Cl⁻ and K⁺ concentrations in the saliva were all significantly increased due to dysfunction of the ducts. Furthermore, Fam20c deficiency significantly increased BMP2 and BMP7 expression, decreased BMP4 expression, and attenuated the canonical and noncanonical BMP signaling pathways in the salivary glands. Collectively, the results of the present study demonstrate that FAM20C is a key regulator of acinar and duct structure and duct maturation and provide a novel avenue for investigating novel therapeutic targets for oral diseases including xerostomia.

Specific ablation of mouse Fam20C in cells expressing type I collagen leads to skeletal defects and hypophosphatemia

FAM20C mutations in humans cause Raine syndrome and our previous studies showed that global inactivation of mouse Fam20C led to bone and dental defects. By crossbreeding 2.3  kb Col 1a1-Cre mice with Fam20C^flox/flox mice, we created 2.3  kb Col 1a1-Cre;Fam20C^foxl/flox (cKO) mice, in which Fam20C was inactivated in cells expressing Type I collagen. This study showed that the long bones of cKO mice were shorter and had a lower level of mineralization compared to the normal mice. The collagen fibrils in Fam20C-deficient bone were disorganized and thicker while the growth plate cartilage in cKO mice was disorganized and wider compared to the normal mice. The Fam20C-deficient bone had a lower level of dentin matrix protein 1, and higher levels of osteopontin and bone sialoprotein than the normal. The blood of cKO mice had an elevated level of fibroblast growth factor 23 and reduced level of phosphorus. These findings indicate that inactivation of Fam20C in cells expressing type I collagen led to skeletal defects and hypophosphatemia. The altered levels of dentin matrix protein 1 and osteopontin in Fam20C-deficient bone may be significant contributors to the mineralized tissue defects in human patients and animals suffering from the functional loss of FAM20C.

Raine Syndrome (OMIM #259775), Caused By FAM20C Mutation, Is Congenital Sclerosing Osteomalacia With Cerebral Calcification (OMIM 259660)

In 1985, we briefly reported infant sisters with a unique, lethal, autosomal recessive disorder designated congenital sclerosing osteomalacia with cerebral calcification. In 1986, this condition was entered into Mendelian Inheritance In Man (MIM) as osteomalacia, sclerosing, with cerebral calcification (MIM 259660). However, no attestations followed. Instead, in 1989 Raine and colleagues published an affected neonate considering unprecedented the striking clinical and radiographic features. In 1992, "Raine syndrome" entered MIM formally as osteosclerotic bone dysplasia, lethal (MIM #259775). In 2007, the etiology emerged as loss-of-function mutation of FAM20C that encodes family with sequence similarity 20, member C. FAM20C is highly expressed in embryonic calcified tissues and encodes a kinase (dentin matrix protein 4) for most of the secreted phosphoproteome including FGF23, osteopontin, and other regulators of skeletal mineralization. Herein, we detail the clinical, radiological, biochemical, histopathological, and FAM20C findings of our patients. Following premortem tetracycline labeling, the proposita's non-decalcified skeletal histopathology after autopsy indicated no rickets but documented severe osteomalacia. Archival DNA revealed the sisters were compound heterozygotes for a unique missense mutation and a novel deletion in FAM20C. Individuals heterozygous for the missense mutation seemed to prematurely fuse their metopic suture and develop a metopic ridge sometimes including trigonocephaly. Our findings clarify FAM20C's role in hard tissue formation and mineralization, and show that Raine syndrome is congenital sclerosing osteomalacia with cerebral calcification. © 2016 American Society for Bone and Mineral Research.

Non lethal Raine syndrome and differential diagnosis

Raine syndrome is a rare autosomal recessive bone dysplasia characterized by characteristic facial features with exophthalmos and generalized osteosclerosis. Amelogenesis imperfecta, hearing loss, seizures, and intracerebral calcification are apparent in some affected individuals. Originally, Raine syndrome was originally reported as a lethal syndrome. However, recently a milder phenotype, compatible with life, has been described. Biallelic variants inFAM20C, encoding aGolgi casein kinase involved in biomineralisation, have been identified in affected individuals. We report here a consanguineous Moroccan family with two affected siblingsa girl aged 18 and a boy of 15years. Clinical features, including learning disability, seizures and amelogenesis imperfecta, initially suggested a diagnosis of Kohlschutter-Tonz syndrome. However,a novel homozygous FAM20Cvariantc.676T > A, p.(Trp226Arg) was identified in the affected siblings. Our report reinforces that Raine syndrome is compatible with life, and that mild hypophosphatemia and amelogenesis imperfecta are key features of the attenuated form.

Loss of epithelial FAM20A in mice causes amelogenesis imperfecta, tooth eruption delay and gingival overgrowth

FAM20A has been studied to a very limited extent. Mutations in human FAM20A cause amelogenesis imperfecta, gingival fibromatosis and kidney problems. It would be desirable to systemically analyse the expression of FAM20A in dental tissues and to assess the pathological changes when this molecule is specifically nullified in individual tissues. Recently, we generated mice with a Fam20A-floxed allele containing the beta-galactosidase reporter gene. We analysed FAM20A expression in dental tissues using X-Gal staining, immunohistochemistry and in situ hybridization, which showed that the ameloblasts in the mouse mandibular first molar began to express FAM20A at 1 day after birth, and the reduced enamel epithelium in erupting molars expressed a significant level of FAM20A. By breeding K14-Cre mice with Fam20A^flox/flox mice, we created K14-Cre;Fam20A^flox/flox (conditional knock out, cKO) mice, in which Fam20A was inactivated in the epithelium. We analysed the dental tissues of cKO mice using X-ray radiography, histology and immunohistochemistry. The molar enamel matrix in cKO mice was much thinner than normal and was often separated from the dentinoenamel junction. The Fam20A-deficient ameloblasts were non-polarized and disorganized and were detached from the enamel matrix. The enamel abnormality in cKO mice was consistent with the diagnosis of amelogenesis imperfecta. The levels of enamelin and matrix metalloproteinase 20 were lower in the ameloblasts and enamel of cKO mice than the normal mice. The cKO mice had remarkable delays in the eruption of molars and hyperplasia of the gingival epithelium. The findings emphasize the essential roles of FAM20A in the development of dental and oral tissues.