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.

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.

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.

Angiofibroma nasofaríngeo juvenil con extensión orbitaria / Juvenile nasopharyngeal angiofibroma with orbital extension

CASO CLÍNICO: Varón de 21 años con historia de exoftalmos izquierdo y diplopía de 2 semanas de evolución. La resonancia magnética mostró una lesión muy vascularizada etmoido-orbitaria con invasión de base del cráneo anterior y extensión orbitaria. La biopsia etmoidal confirmó un tejido fibrovascular compatible con angiofibroma. DISCUSIÓN: El angiofibroma nasofaríngeo juvenil (ANJ) es un tumor benigno con características locales de malignidad debido a su capacidad de invadir áreas adyacentes. En nuestro caso, el comienzo se presenta con manifestaciones de extensión orbitaria. Consideramos necesario un conocimiento amplio y un abordaje multidisciplinario con el fin de mejorar el pronóstico

CLINICAL CASE: The case is presented of a 21 year-old male with a history of left proptosis and diplopia of two weeks of onset. The MRI showed an ethmoid-orbital vascular lesion with anterior skull base invasion and orbital extension. Biopsy of the ethmoid confirmed fibrovascular tissue, which supported the diagnosis of angiofibroma. DISCUSSION: It is a benign neoplasm with local characteristics of malignancy due to its ability to invade adjacent areas. In this case, the debut presented with manifestations of orbital extension. A broad and multidisciplinary approach is needed in order to improve prognosis

Secreted kinase phosphorylates extracellular proteins that regulate biomineralization.

Protein phosphorylation is a fundamental mechanism regulating nearly every aspect of cellular life. Several secreted proteins are phosphorylated, but the kinases responsible are unknown. We identified a family of atypical protein kinases that localize within the Golgi apparatus and are secreted. Fam20C appears to be the Golgi casein kinase that phosphorylates secretory pathway proteins within S-x-E motifs. Fam20C phosphorylates the caseins and several secreted proteins implicated in biomineralization, including the small integrin-binding ligand, N-linked glycoproteins (SIBLINGs). Consequently, mutations in Fam20C cause an osteosclerotic bone dysplasia in humans known as Raine syndrome. Fam20C is thus a protein kinase dedicated to the phosphorylation of extracellular proteins.

ABCA5 resides in lysosomes, and ABCA5 knockout mice develop lysosomal disease-like symptoms.

ABCA5 is a member of the ABC transporter A subfamily, and a mouse orthologue (mABCA5) in newborn mouse brain and neural cells was identified by reverse transcription-PCR. Full-length cDNA cloning revealed that mABCA5 consists of 1,642 amino acid residues and that its putative structure is that of a full-type ABC transporter having two sets of six transmembrane segments and a nucleotide binding domain. Immunohistochemical studies revealed that mABCA5 is expressed in brain, lung, heart, and thyroid gland. A subcellular localization analysis showed that mABCA5 is a resident of lysosomes and late endosomes. Abca5(-)(/)(-) mice exhibited symptoms similar to those of several lysosomal diseases in heart, although no prominent abnormalities were found in brain or lung. They developed a dilated cardiomyopathy-like heart after reaching adulthood and died due to depression of the cardiovascular system. In addition, Abca5(-)(/)(-) mice also exhibited exophthalmos and collapse of the thyroid gland. Therefore, ABCA5 is a protein related to a lysosomal disease and plays important roles, especially in cardiomyocytes and follicular cells.

Exophthalmos in Cushing's syndrome.

OBJECTIVE: Exophthalmos was noted in 4 of the 12 patients reported by Harvey Cushing in 1932. Although exophthalmos has often been included in clinical descriptions, no previous study has reported actual measurements in patients with active and treated Cushing's syndrome, and in control patients. The aim of this study was to obtain these measurements. PATIENTS: Thirty-one patients with active Cushing's syndrome (19 iatrogenic), 15 with treated Cushing's syndrome, 18 with Graves' ophthalmopathy, 59 control patients, and 3 patients with active Cushing's syndrome plus a family or personal history of thyroid disease. DESIGN AND MEASUREMENTS: A consecutive series of patients with active and treated Cushing's syndrome were assessed. They were compared with patients with Graves' ophthalmopathy, and with control patients. Exophthalmos was assessed by the author using a Hertel meter. Urinary free cortisol was measured on patients with Cushing's syndrome, and serum thyroxine was estimated for them, and for the patients with Graves' ophthalmopathy. RESULTS: Exophthalmos exceeding 16 mm (> 2 SD above normal mean) was found in 45% of active Cushing's syndrome, 21% of iatrogenic Cushing's syndrome, 20% of treated Cushing's syndrome, 2% of normal controls, and 77% of patients with Graves' ophthalmopathy. No patient with Cushing's syndrome had significant symptoms due to exophthalmos. CONCLUSION: Patients with active Cushing's syndrome have statistically significant exophthalmos. This rarely causes symptoms, and diminishes when cortisol concentrations become normal. Cushing's syndrome and autoimmune thyroid disease may coexist in patients with exophthalmos.

Glycosaminoglycans in thyroid-associated ophthalmopathy.

Glycosaminoglycan (GAG) accumulation in the retrobulbar space of patients with thyroid-associated ophthalmopathy (TAO) has been documented in a number of immunohistochemical studies. In order to gain further insight into possible immunopathogenic mechanisms, the influence of humoral immunity on retrobulbar fibroblasts (RF) as GAG producing cells as well as on GAGs themselves was investigated. The effect of lymphocytes on hyaluronic acid (HA) synthesis of RF as well as in turn the influence of RF on lymphocytes were evaluated. In search of methods which would facilitate management of patients with TAO and allow assessment of disease activity, GAGs were determined in both urine and plasma. Immunoglobulin G (IgG) of patients with TAO were found to markedly stimulate the 3H-GAG secretion of RF. Patients with TAO exhibited significantly greater antibody values directed against HA than controls. Preliminary results concerning the influence of lymphocytes on RF indicate a tendency for patients' lymphocytes to increase the synthesis of HA. Furthermore, these lymphocytes in turn were stimulated more by irradiated autologous RF than by irradiated heterologous RF. Urine and plasma GAG determination proved to be suitable for the routine assessment of disease activity and outcome of therapy. In conclusion, GAGs seem to play an important role in the pathogenesis of the disease and their measurement may provide aid to the endocrinological evaluation of patients with TAO.

The permeability of the corneal epithelium of Graves' ophthalmopathy as determined by fluorophotometry.

The function of the corneal epithelium was evaluated in 30 patients with Graves' ophthalmopathy in whom no signs of corneal disease were observed. This function was evaluated by determining the permeability values of the corneal epithelium for fluorescein using fluorophotometry. The permeability values of the patients were compared with those of 46 healthy individuals. A significant increase in the permeability values was seen in 11 (37%) patients and in two (4%) controls (p less than 0.05). The difference in the mean permeability values between patients en controls was statistically significant (0.053 nm/sec. +/- 0.043 SD and 0.038 nm/sec. +/- 0.017 SD, respectively, p less than 0.05). No relation was found between the permeability values of the corneal epithelium and the NOSPECS classification or the duration of the disease. There was a tendency for increased permeability values in patients having an exophthalmos larger than 20 mm. (correl. coeff. = + 0.3, p less than 0.05).

Correlation between unilateral exophthalmos and thyroid diseases.

43 clinically euthyroid patients with unilateral exophthalmos were examined using clinical methods, echography, and computerized tomography. The functioning of the hypothalamic-hypophyseal-thyroid axis was investigated by measurements of TSH (before and after stimulation with TRH), thyroid hormones and antithyroglobulin antibodies. After a review of the literature, the results are discussed.

Cytoenzymology and 3H-thymidine uptake of retro-ocular connective tissue cultures in experimental endocrino-exophthalmos.

The in vitro retro-ocular connective tissue cultures from guinea pigs with endocrine exophthalmos were studied before and after retro-ocular treatment with cortisol and hyaluronidase. Both cortisol and hyaluronidase inhibited the cell proliferation, the cytoenzymic activities of oxydoreductases, the 3H-thymidine uptake, the number of mitoses and the protein content of cultivated cells.

Experimental exophthalmos. Binding of thyrotropin and an exophthalmogenic factor derived from thyrotropin to retro-orbital tissue plasma membranes.

Biologically active preparations of 125I-thyrotropin, [3H]thyrotropin, and the [3H]exophthalmogenic factor derived from thyrotropin by partial pepsin digestion have been used to study the binding properties of the thyrotropin receptor on guinea pig retro-orbital tissue plasma membranes. In regard to the optimal conditions of binding, pH, buffer, salt concentrations, and temperature, these properties are the same as those described in any accompanying report concerning thyrotropin binding to bovine thyroid plasma membranes (Tate, R.L., Schwartz, H.I., Holmes, J.M., Kohn, L.D., and Winand, R.J. (1975) J. Biol. Chem. 250, 6509-6515). In addition, thyrotropin receptors on the retro-orbital tissue plasma membranes are similar to thyrotropin receptors on bovine thyroid plasma membranes in their apparent negative cooperativity and in their relative affinities for luteinizing hormone, the beta subunit of thyrotropin, and the alpha subunit of thyrotropin. In contrast, gamma-globulin from patients with malignant exophthalmos enhances binding when added to incubation mixtures containing the retro-orbital tissue plasma membranes but not when added to those containing thyroid plasma membranes. Normal gamma-globulin and gamma-globulin from Graves' disease patients without exophthalmos do not have this property. The gamma-globulin itself does not bind to the membrane except in the presence of thyrotropin or its exophthalmogenic factor derivative. Tryptic digestion of the retro-orbital tissue membranes releases specific thyrotropin and exophthalmogenic factor binding activity into the supernatant phase. Chromatography on Sephadex G-100 indicates that this trypsin-released receptor activity has a molecular weight of 75,000 or greater, rather than 15,000 to 30,000 for the trypsin-released receptor activity from bovine thyroid membranes (Tate, R.L., Schwartz, H.I., Holmes, J.M., Kohn, L.D., and Winand, R.J. (1975) J. Biol. Chem. 250, 6509-6515).

Possible stimulation of thermogenesis in brown adipose tissue by thyroid-stimulating hormone.

It is suggested that in addition to stimulating the thyroid gland (i.e., the main regulator of metabolic-rate in adults) thyroid-stimulating hormone (T.S.H.) stimulates the second thermoregulatory organ (i.e., the brown adipose tissue). Brown fat functions as a thermogenic organ in hibernating animals, in newborn infants, and during cold acclimatisation. However, B.F. may persist in childhood and in some adults. Its hypertrophy in response to T.S.H. could account for certain unexplained features of myxoedema in which serum-T.S.H. is raised, such as swelling of the supraclavicular fat pad and the less commonly encountered symptoms of ascites or pericardial and pleural serous effusions which can persist for years in undiagnosed cases and respond rapidly to thyroxine when serum-T.S.H. returns to normal. Lack of thyroxine is not the cause of these features since they are not found in pituitary myxoedema, where thyroid hormone levels are as low but T.S.H. is absent.

Production and measurement of exophthalmos-producing factor in guinea pigs.

Although the extent of proptosis in exophthalmic Graves' disease has been measured directly and shown to correlate with serum content of a bioassayable exophthalmus-producing factor (EPS;1), a comparable relationship in an experimental model has not been reported. Progressive exophthalmos, measured from photographs and expressed as a ratio of intercorneal distance to intersupraorbital ridge distance, was produced in male guinea pigs when thyroid status was altered either by surgical thyroidectomy supplemented with 131-I treatment or by the administration of 6-propyl-2 thiouracil (0.1% in chow). In both groups, at time of sacrifice, serum content of EPF estimated by a modified goldfish bioassay using a known exophthalmogeric TSH preparation (Ambinon, Organon-Oss) as standard was positively correlated (r equals 0.804) with the terminal degree of exophthalmos. Daily replacement therapy with T4 (15mug/kg body wt) failed to alter significantly the exophthalmos which developed, even when replacement was initiated prior to the alterations of thyroid gland function; this observation tends to eliminate thyroid hormone deficiency per se as the causal event in exophthalmos. T4 treatment did, however, reverse or prevent the rises in serum TSH levels (McKenzie bioassay) thus dissociating TSH activity from EPF activity in the guinea pig. Treatment of guinea pigs with synthetic TRH (0.5, 1.0 OR 10 mug/kg body wt) for 21 days failed to produce demonstrable exophthalmos or assayable EPF levels although plasma TSH was significantly elevated.