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.

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.

Variability of systemic and oro-dental phenotype in two families with non-lethal Raine syndrome with FAM20C mutations.

BACKGROUND: Raine syndrome (RS) is a rare autosomal recessive bone dysplasia typified by osteosclerosis and dysmorphic facies due to FAM20C mutations. Initially reported as lethal in infancy, survival is possible into adulthood. We describe the molecular analysis and clinical phenotypes of five individuals from two consanguineous Brazilian families with attenuated Raine Syndrome with previously unreported features. METHODS: The medical and dental clinical records were reviewed. Extracted deciduous and permanent teeth as well as oral soft tissues were analysed. Whole exome sequencing was undertaken and FAM20C cDNA sequenced in family 1. RESULTS: Family 1 included 3 siblings with hypoplastic Amelogenesis Imperfecta (AI) (inherited abnormal dental enamel formation). Mild facial dysmorphism was noted in the absence of other obvious skeletal or growth abnormalities. A mild hypophosphataemia and soft tissue ectopic mineralization were present. A homozygous FAM20C donor splice site mutation (c.784 + 5 g > c) was identified which led to abnormal cDNA sequence. Family 2 included 2 siblings with hypoplastic AI and tooth dentine abnormalities as part of a more obvious syndrome with facial dysmorphism. There was hypophosphataemia, soft tissue ectopic mineralization, but no osteosclerosis. A homozygous missense mutation in FAM20C (c.1487C > T; p.P496L) was identified. CONCLUSIONS: The clinical phenotype of non-lethal Raine Syndrome is more variable, including between affected siblings, than previously described and an adverse impact on bone growth and health may not be a prominent feature. By contrast, a profound failure of dental enamel formation leading to a distinctive hypoplastic AI in all teeth should alert clinicians to the possibility of FAM20C mutations.

Clinical relevance of "bulging eyes" for the differential diagnosis of spinocerebellar ataxias.

OBJECTIVE: To investigate the relevance of the clinical finding of bulging eyes (BE) in a large Brazilian cohort of spinocerebellar ataxias (SCA), to assess its importance in clinical differential diagnosis among SCA. METHODS: Three hundred sixty-nine patients from 168 Brazilian families with SCA were assessed with neurological examination and molecular genetic testing. BE was characterized by the presence of eyelid retraction. Genetically ascertained SCA3 was detected in 167 patients, SCA10 in 68 patients, SCA2 in 20, SCA1 in 9, SCA7 in 6, and SCA6 in 3 patients. RESULTS: BE was detected in 123 patients with SCA (33.3%), namely 109 of the 167 SCA3 patients (65.3%) and in 5 of the others SCA patients (1 SCA10 patient, 2 SCA1 patients and 2 SCA2 patients). CONCLUSION: BE was detected in the majority of patients with SCA3 (65.3%) and could be used with a clinical tool for the differential diagnosis of SCA.

Clinical relevance of "bulging eyes" for the differential diagnosis of spinocerebellar ataxias / Relevância clínica do "bulging eyes" para o diagnóstico diferencial das ataxias espinocerebelares

Objective To investigate the relevance of the clinical finding of bulging eyes (BE) in a large Brazilian cohort of spinocerebellar ataxias (SCA), to assess its importance in clinical differential diagnosis among SCA. Methods Three hundred sixty-nine patients from 168 Brazilian families with SCA were assessed with neurological examination and molecular genetic testing. BE was characterized by the presence of eyelid retraction. Genetically ascertained SCA3 was detected in 167 patients, SCA10 in 68 patients, SCA2 in 20, SCA1 in 9, SCA7 in 6, and SCA6 in 3 patients. Results BE was detected in 123 patients with SCA (33.3%), namely 109 of the 167 SCA3 patients (65.3%) and in 5 of the others SCA patients (1 SCA10 patient, 2 SCA1 patients and 2 SCA2 patients). Conclusion BE was detected in the majority of patients with SCA3 (65.3%) and could be used with a clinical tool for the differential diagnosis of SCA. .

Objetivo Investigar a relevância do achado clínico de bulging eyes (BE) em uma grande amostra brasileira de pacientes com ataxias espinocerebelares (AEC), para avaliar sua importância no diagnóstico diferencial entre as AEC. Métodos Foram avaliados 369 pacientes de 168 famílias brasileiras com AEC através de exame neurológico e testes de genética molecular. BE foi caracterizado pela presença de retração palpebral. AEC3 foi determinada geneticamente em 167 pacientes, AEC10 em 68 pacientes, AEC2 em 20, AEC1 em 9, AEC7 em 6 e AEC6 foi encontrada em 3 pacientes. Resultados BE foi detectado em 123 pacientes com AEC (33,3%), correspondendo a 109 dos 167 pacientes com AEC3 (65,3%) e 5 pacientes com outras AEC (1 paciente com AEC10, 2 AEC1 e 2 pacientes com AEC2). Conclusão BE foi detectado na maioria dos pacientes com AEC3 (65,3%) e poderia ser usado com uma ferramenta clínica para o diagnóstico diferencial das AEC. .

Raine dysplasia: a Brazilian case with a mild radiological involvement.

We report a preterm male infant, the first child of a young consanguineous couple, whose physical examination revealed craniofacial disproportion with microcephaly, wide fontanelles, exophthalmos, low nasal root and hypoplastic nose, long philtrum, small mouth, high arched and narrow palate, micrognathia, dysplastic, low-set and rounded ears, short neck and, arthrogryposis. Postmortem findings included hypoplastic lungs. Radiological examinations showed mild and localized increased of bone density in the cranial vault and skull base and facial bones and undermodelled in the long bones. The above findings are characteristics of Raine dysplasia but the case reported here presents a mild bone involvement with only a localized bone sclerosis and absence of prenatal fractures. We discuss the possibility that this case represents an allelic mutation of the Raine gene. The consanguinity of the parents reinforces the hypothesis of autosomal recessive inheritance for this entity.