A Novel Missense Mutation of NOG Interferes With the Dimerization of NOG and Causes Proximal Symphalangism Syndrome in a Chinese Family

Identification of a novel nonsense NOG mutation in a patient with stapes ankylosis and symphalangism spectrum disorder

Multiple bone disorders due to mutations in the human noggin (NOG) causes a variety of phenotypes. Hearing impairment due to stapes ankylosis secondary to bony degeneration is also a feature of these syndromes. We describe the case of an individual in a Japanese family with conductive hearing loss due to stapes ankylosis and hyperopia and dactylosymphysis. We revealed a novel NOG mutation, NM_005450.6:c.222 C > A / p.Tyr74*, and confirmed genetic significance.

TMEM165 a new player in proteoglycan synthesis: loss of TMEM165 impairs elongation of chondroitin- and heparan-sulfate glycosaminoglycan chains of proteoglycans and triggers early chondrocyte differentiation and hypertrophy

TMEM165 deficiency leads to skeletal disorder characterized by major skeletal dysplasia and pronounced dwarfism. However, the molecular mechanisms involved have not been fully understood. Here, we uncover that TMEM165 deficiency impairs the synthesis of proteoglycans by producing a blockage in the elongation of chondroitin-and heparan-sulfate glycosaminoglycan chains leading to the synthesis of proteoglycans with shorter glycosaminoglycan chains. We demonstrated that the blockage in elongation of glycosaminoglycan chains is not due to defect in the Golgi elongating enzymes but rather to availability of the co-factor Mn²⁺. Supplementation of cell with Mn²⁺ rescue the elongation process, confirming a role of TMEM165 in Mn²⁺ Golgi homeostasis. Additionally, we showed that TMEM165 deficiency functionally impairs TGFβ and BMP signaling pathways in chondrocytes and in fibroblast cells of TMEM165 deficient patients. Finally, we found that loss of TMEM165 impairs chondrogenic differentiation by accelerating the timing of Ihh expression and promoting early chondrocyte maturation and hypertrophy. Collectively, our results indicate that TMEM165 plays an important role in proteoglycan synthesis and underline the critical role of glycosaminoglycan chains structure in the regulation of chondrogenesis. Our data also suggest that Mn²⁺ supplementation may be a promising therapeutic strategy in the treatment of TMEM165 deficient patients.

Genetic and clinical phenotypic analysis of familial stapes sclerosis caused by an NOG mutation

Background

The noggin protein encoded by the NOG gene can interfere with the binding of bone morphogenetic protein to its receptor, thus affecting bone and joint development. The symptoms include abnormal skeletal development and conductive deafness.

Methods

In a retrospective study, clinical data of the proband and her family members, including 8 people and 50 healthy normal controls, were collected. Second-generation sequencing was performed on peripheral blood samples from them.

Results

The sequencing analysis indicated that in the proband, the NOG gene had a c.532T > C, p.C178R (cytosine deletion, NM_005450.6:c.532T > C), leading to an amino acid change. The proband's father, grandmother, second sister, and third sister also had this mutation, whereas family members with normal phenotypes did not have the mutation.

Conclusion

Analysis of this family showed that the novel presentation of the c.532T > C, p.C178R mutation in the NOG gene resulted in syndrome-type autosomal dominant inheritance reflected in a mild clinical phenotype, which is of great importance for further studies of the clinical phenotype and pathogenesis of stapes sclerosis.

Novel NOG (p.P42S) mutation causes proximal symphalangism in a four-generation Chinese family

Background

Proximal symphalangism (SYM1; OMIM 185800), also called Cushing’s symphalangism, is an infrequent autosomal dominant disease. An SYM1 patient typically features variable fusion of proximal interphalangeal joints in the hands and feet.

Methods

We recruited a four-generation Chinese non-consanguineous family with SYM1. We examined their hands and feet using X-rays to confirm fusion of proximal interphalangeal joints. We evaluated their audiology using standard audiometric procedures and equipment. Then, we identified genetic variants using whole exome sequencing and validated mutations using Sanger sequencing. Mutation pathogenicity was analyzed with bioinformatics.

Results

Radiographs revealed proximal-joint fusion of fingers and toes in the patients. Two elderly individuals (II:1 and II:4) exhibited slight hearing loss. Additionally, we detected a novel heterozygous missense mutation in exon 1 of NOG (NM_005450) c.124C > T, p.(Pro42Ser) in all patients. This c.124C > T mutation is highly conserved across multiple species and the p.(Pro42Ser) variation is potentially highly pathogenic.

Conclusion

Our results suggest that heterozygous c.124C > T, p.(Pro42Ser) in NOG is a novel mutation that causes human SYM1 phenotype.

Electronic supplementary material

The online version of this article (10.1186/s12881-019-0864-1) contains supplementary material, which is available to authorized users.

Identification of a Novel NOG Missense Mutation in a Chinese Family With Symphalangism and Tarsal Coalitions

Background

Proximal symphalangism (SYM1) is a rare genetic bone disorder characterized by the fusion of proximal interphalangeal joints in the hands and feet. Genetic studies have identified two genes underlying SYM1 as the noggin (NOG) and the growth differentiation factor 5 (GDF5).

Case Report

In the present report, a 43-year-old gravida at 11 weeks of gestation was referred for evaluation of abnormal fusions of the joints. In the initial diagnosis, physical examination was undertaken. However, traditional radiological examination was not applied due to the need to protect the fetus, making diagnosis results inefficient to determine the exact disease affecting the proband. To acquire alternative clinical evidences, we conducted radiological examinations on two other affected family members. The radiological examination revealed that they carried the symphalangism accompanied with tarsal coalition, a very rare manifestation of SYM1. A combination of whole exome sequencing (WES) and Sanger sequencing revealed a novel heterozygous missense mutation (c.163G > T; p.Asp55Tyr) in the NOG gene, which could be associated with the observed pathogenic SYM1 in the studied family. The p.Asp55Tyr mutation co-segregated with SYM1 through the affected and unaffected family members. In silico structural modeling of the p.Asp55Tyr mutation showed that it abolishes the interaction with the Arg167 residue and causes a change in the electrostatic potential profile of the type II binding site of the noggin protein.

Conclusion

Our findings indicate that the genetic test based on WES can be useful in diagnosing SYM1 patients, with particular advantages in preventing the fetus from contacting harmful X-ray through the traditional radiography. The novel pathogenic mutation identified would further expand our understanding of the mutation spectrum of NOG in association with SYM1 disease and provide a guidance on how to determine whether the fetus is affected by SYM1 through the prenatal diagnosis.

A novel nonsense mutation in the NOG gene causes familial NOG-related symphalangism spectrum disorder

The human noggin (NOG) gene is responsible for a broad spectrum of clinical manifestations of NOG-related symphalangism spectrum disorder (NOG-SSD), which include proximal symphalangism, multiple synostoses, stapes ankylosis with broad thumbs (SABTT), tarsal–carpal coalition syndrome, and brachydactyly type B2. Some of these disorders exhibit phenotypes associated with congenital stapes ankylosis. In the present study, we describe a Japanese pedigree with dactylosymphysis and conductive hearing loss due to congenital stapes ankylosis. The range of motion in her elbow joint was also restricted. The family showed multiple clinical features and was diagnosed with SABTT. Sanger sequencing analysis of the NOG gene in the family members revealed a novel heterozygous nonsense mutation (c.397A>T; p.K133*). In the family, the prevalence of dactylosymphysis and hyperopia was 100% while that of stapes ankylosis was less than 100%. Stapes surgery using a CO₂ laser led to a significant improvement of the conductive hearing loss. This novel mutation expands our understanding of NOG-SSD from clinical and genetic perspectives.

BMP signalling in skeletal development, disease and repair

Since the identification in 1988 of bone morphogenetic protein 2 (BMP2) as a potent inducer of bone and cartilage formation, BMP superfamily signalling has become one of the most heavily investigated topics in vertebrate skeletal biology. Whereas a large part of this research has focused on the roles of BMP2, BMP4 and BMP7 in the formation and repair of endochondral bone, a large number of BMP superfamily molecules have now been implicated in almost all aspects of bone, cartilage and joint biology. As modulating BMP signalling is currently a major therapeutic target, our rapidly expanding knowledge of how BMP superfamily signalling affects most tissue types of the skeletal system creates enormous potential to translate basic research findings into successful clinical therapies that improve bone mass or quality, ameliorate diseases of skeletal overgrowth, and repair damage to bone and joints. This Review examines the genetic evidence implicating BMP superfamily signalling in vertebrate bone and joint development, discusses a selection of human skeletal disorders associated with altered BMP signalling and summarizes the status of modulating the BMP pathway as a therapeutic target for skeletal trauma and disease.