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 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.

Hereditary deletion of the entire FAM20C gene in a patient with Raine syndrome.

Raine syndrome is an autosomal recessive disorder caused by mutations in the FAM20C gene that is characterized by generalized osteosclerosis with periosteal new bone formation and distinctive craniofacial dysmorphism. We report on a child who is homozygous for a 487-kb deletion in 7p22.3 that contains FAM20C. Both parents were heterozygous for the deletion. Our patient had the common craniofacial features as well as, uncommon features such as protruding tongue, short stature, and hypoplastic distal phalanges. In addition, he had wormian bones and pyriform aperture stenosis, features that are usually under diagnosed. It is clear that Raine syndrome has a wide range of expression and may not be lethal in the neonatal period. Furthermore, Raine cases due to whole gene deletion do not seem to have a major difference in the phenotype over those caused by various mutations.

[Neuro-surgical exophthalmias (retrospective study of 27 cases at the C.H.U. of Dakar)]. / Exophtalmies neuro-chirurgicales (etude rétrospective de 27 cas au C.H.U. de Dakar).

The report covers 27 cases of neuro-surgical exophthalmia treated at Dakar U.H.C. between 1970 and 1987. Unilateral forms are the most common (25 cases), usually discovered at the bulging stage. Exploration was undertaken by the usual means of X-ray without contrast, echography, arteriography, and fractioned, gaseous encephalography employed together in varying degrees. The main etiologies are tumours (70%), largely benign, and specific and non-specific inflammation (18.5%). Surgery was prescribed in 18 cases, including 11 orbitotomies--8 frontal and 3 fronto-temporal. Malformation syndromes, and above all very advanced pathologies challenged surgical skill in 9 of the cases. Generally speaking, post operational results are favourable, but 3 deaths are reported and one relapse. Tomodensitometry, modern anaesthetic and revival techniques, and the important collaboration between the ophthalmologist and the neuro-surgeon are all factors in successfully mastering neuro-surgical protrusions.