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.

Novel homozygous OSGEP gene pathogenic variants in two unrelated patients with Galloway-Mowat syndrome: case report and review of the literature.

BACKGROUND: Galloway-Mowat syndrome (GAMOS) is a rare autosomal recessive disorder characterized by early-onset nephrotic syndrome and microcephaly with brain anomalies. WDR73 pathogenic variants were described as the first genetic cause of GAMOS and, very recently, four novel causative genes, OSGEP, LAGE3, TP53RK, and TPRKB, have been identified. CASE PRESENTATION: We present the clinical and genetic characteristics of two unrelated infants with clinical suspicion of GAMOS who were born from consanguineous parents. Both patients showed a similar clinical presentation, with early-onset nephrotic syndrome, microcephaly, brain atrophy, developmental delay, axial hypotonia, and early fatality. We identified two novel likely disease-causing variants in the OSGEP gene. These two cases, in conjunction with the findings of a literature review, indicate that OSGEP pathogenic variants are associated with an earlier onset of nephrotic syndrome and shorter life expectancy than WDR73 pathogenic variants. CONCLUSIONS: Our findings expand the spectrum of pathogenic variants in the OSGEP gene and, taken in conjunction with the results of the literature review, suggest that the OSGEP gene should be considered the main known monogenic cause of GAMOS. Early genetic diagnosis of GAMOS is of paramount importance for genetic counseling and family planning.

Congenital Zika Syndrome: The Main Cause of Death and Correspondence Between Brain CT and Postmortem Histological Section Findings From the Same Individuals.

In the present case series, the cause of death of infants diagnosed with congenital Zika syndrome (CZS) was lung disease (pneumonia and sepsis with massive pulmonary aspiration), probably secondary to dysphagia and reflux. The main findings in infants with a confirmed diagnosis of CZS who died were as follows: (1) calcification and hypoplasia of the lentiform nuclei, hypoplasia of the caudate nuclei, and calcification at the cortical-subcortical junction was noted in all cases (100%) and calcification of the caudate nuclei was noted in 66.7% of cases; (2) calcification in the brainstem and along the lateral wall of the lateral ventricles was noted in only the case with arthrogryposis (33.3%); and (3) lesions in the posterior fossa (hypoplasia of the brainstem and cerebellum) were noted in two cases (66.7%), including the case with arthrogryposis. The findings concerning calcifications and brain malformations obtained from non-contrast computed tomography (CT) demonstrated good agreement with findings obtained from the postmortem pathological analysis; however, CT failed to detect discontinuity of the pia mater with heterotopia, invasion of the cerebral tissue into the subarachnoid space, and discontinuity of the ependyma in the lateral ventricles with gliosis; this last feature was only imaged in the most severe case of extreme microcephaly with a simplified gyral pattern. Only histopathology showed grouped calcifications associated with scattered calcifications suggestive of the neuron morphology.

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.

Centrosome amplification causes microcephaly.

Centrosome amplification is a hallmark of human tumours. In flies, extra centrosomes cause spindle position defects that result in the expansion of the neural stem cell (NSC) pool and consequently in tumour formation. Here we investigated the consequences of centrosome amplification during mouse brain development and homeostasis. We show that centrosome amplification causes microcephaly due to inefficient clustering mechanisms, where NSCs divide in a multipolar fashion producing aneuploid cells that enter apoptosis. Importantly, we show that apoptosis inhibition causes the accumulation of highly aneuploid cells that lose their proliferative capacity and differentiate, thus depleting the pool of progenitors. Even if these conditions are not sufficient to halt brain development, they cause premature death due to tissue degeneration. Our results support an alternative concept to explain the etiology of microcephaly and show that centrosome amplification and aneuploidy can result in tissue degeneration rather than overproliferation and cancer.