Keutel Syndrome Research Articles

Biochemical Significance of Matrix Gla Protein and Its Potential Use as a Marker in Clinical Biochemistry

The aim of this work was to present an overview on the biochemical significance of the matrix γ‑carboxyglutamate (Gla) protein (MGP). According to the literature, the MGP is associated with vascular, bone, and kidney metabolisms, as well asvitamin K levels. The relationship of MGP to Keutel's syndrome, Pseudoxanthoma elasticum, colitis, and dental calculus is described. The information published so far suggests that MGP protein levels could have potential as a biochemical marker in these serious diseases.

Specific heterozygous variants in MGP lead to endoplasmic reticulum stress and cause spondyloepiphyseal dysplasia

Matrix Gla protein (MGP) is a vitamin K-dependent post-translationally modified protein, highly expressed in vascular and cartilaginous tissues. It is a potent inhibitor of extracellular matrix mineralization. Biallelic loss-of-function variants in the MGP gene cause Keutel syndrome, an autosomal recessive disorder characterized by widespread calcification of various cartilaginous tissues and skeletal and vascular anomalies. In this study, we report four individuals from two unrelated families with two heterozygous variants in MGP, both altering the cysteine 19 residue to phenylalanine or tyrosine. These individuals present with a spondyloepiphyseal skeletal dysplasia characterized by short stature with a short trunk, diffuse platyspondyly, midface retrusion, progressive epiphyseal anomalies and brachytelephalangism. We investigated the cellular and molecular effects of one of the heterozygous deleterious variants (C19F) using both cell and genetically modified mouse models. Heterozygous ‘knock-in’ mice expressing C19F MGP recapitulate most of the skeletal anomalies observed in the affected individuals. Our results suggest that the main underlying mechanism leading to the observed skeletal dysplasia is endoplasmic reticulum stress-induced apoptosis of the growth plate chondrocytes. Overall, our findings support that heterozygous variants in MGP altering the Cys19 residue cause autosomal dominant spondyloepiphyseal dysplasia, a condition distinct from Keutel syndrome both clinically and molecularly.

Assessment of MGP gene expression in cancer and contribution to prognosis

Matrix Gla protein (MGP) was first identified as a calcification physiological inhibitor and the causal agent of the Keutel syndrome. MGP has been suggested to play a role in development, cell differentiation, and tumorigenesis. This study aimed to compare MGP expression and methylation status in different tumors and adjacent tissues, using The Cancer Genome Atlas (TCGA) data repository. We investigated if changes in MGP mRNA expression were correlated to cancer progression and whether the correlation coefficients could be used for prognosis. Strong correlations were observed between altered MGP levels and disease progression in breast, kidney, liver, and thyroid cancers, suggesting that it could be used to complement current clinical biomarker assays, for early cancer diagnosis.We have also analyzed MGP methylation and identified CpG sites in its promoter and first intron with clear differences in methylation status between healthy and tumoral tissue providing evidence for epigenetic regulation of MGP transcription. Furthermore, we demonstrate that these alterations correlate with the overall survival of the patients suggesting that its assessment can serve as an independent prognostic indicator of patients’ survival.

Very Rare Cause of Fixed Obstruction and Severe Asthma: A Case with Keutel Syndrome

Keutel syndrome is rare inherited disorder with mutations in the matrix G1a protein (MGP). Most of the patient is diagnosed in early childhood. They admitted to the hospital due to hearing loss, recurrent upper respiratory tract infections, chronic cough. In this case report Keutel syndrome is discussed in an adult patient.

Prevention of Arterial Elastocalcinosis: Differential Roles of the Conserved Glutamic Acid and Serine Residues of Matrix Gla Protein.

Inactivating mutations in matrix Gla protein (MGP) lead to Keutel syndrome, a rare disease hallmarked by ectopic calcification of cartilage and vascular tissues. Although MGP acts as a strong inhibitor of arterial elastic lamina calcification (elastocalcinosis), its mode of action is unknown. Two sets of conserved residues undergoing posttranslational modifications-4 glutamic acid residues, which are γ-carboxylated by gamma-glutamyl carboxylase; and 3 serine residues, which are phosphorylated by yet unknown kinase(s)-are thought to be essential for MGP's function. We pursued a genetic approach to study the roles of MGP's conserved residues. First, a transgenic line (SM22a-GlamutMgp) expressing a mutant form of MGP, in which the conserved glutamic acid residues were mutated to alanine, was generated. The transgene was introduced to Mgp-/- mice to generate a compound mutant, which produced the mutated MGP only in the vascular tissues. We generated a second mouse model (MgpS3mut/S3mut) to mutate MGP's conserved serine residues to alanine. The initiation and progression of vascular calcification in these models were analyzed by alizarin red staining, histology, and micro-computed tomography imaging. On a regular diet, the arterial walls in the Mgp-/-; SM22α-GlamutMgp mice were not calcified. However, on a high phosphorus diet, these mice showed wide-spread arterial calcification. In contrast, MgpS3mut/S3mut mice on a regular diet recapitulated arterial calcification traits of Mgp-/- mice, although with lesser severity. For the first time, we show here that MGP's conserved serine residues are indispensable for its antimineralization function in the arterial tissues. Although the conserved glutamic acid residues are not essential for this function on a regular diet, they are needed to prevent phosphate-induced arterial elastocalcinosis.

Keutel Syndrome, a Review of 50 Years of Literature.

Keutel syndrome (KS) is a rare autosomal recessive genetic disorder that was first identified in the beginning of the 1970s and nearly 30 years later attributed to loss-of-function mutations in the gene coding for the matrix Gla protein (MGP). Patients with KS are usually diagnosed during childhood (early onset of the disease), and the major traits include abnormal calcification of cartilaginous tissues resulting in or associated with malformations of skeletal tissues (e.g., midface hypoplasia and brachytelephalangism) and cardiovascular defects (e.g., congenital heart defect, peripheral pulmonary artery stenosis, and, in some cases, arterial calcification), and also hearing loss and mild developmental delay. While studies on Mgp–/– mouse, a faithful model of KS, show that pathologic mineral deposition (ectopic calcification) in cartilaginous and vascular tissues is the primary cause underlying many of these abnormalities, the mechanisms explaining how MGP prevents abnormal calcification remain poorly understood. This has negative implication for the development of a cure for KS. Indeed, at present, only symptomatic treatments are available to treat hypertension and respiratory complications occurring in the KS patients. In this review, we summarize the results published in the last 50 years on Keutel syndrome and present the current status of the knowledge on this rare pathology.

Evaluation of MGP gene expression in colorectal cancer

PurposeMatrix Gla protein (MGP) is a vitamin K-dependent, γ-carboxylated protein that was initially found to be a physiological inhibitor of ectopic calcifications affecting mainly cartilage and the vascular system. Mutations in the MGP gene were found to be responsible for a human pathology, the Keutel syndrome, characterized by abnormal calcifications in cartilage, lungs, brain and vascular system. MGP was recently implicated in tumorigenic processes such as angiogenesis and shown to be abnormally regulated in several tumors, including cervical, ovarian, urogenital and breast. This fact has triggered our interest in analyzing the expression of MGP and of its regulator, the transcription factor runt related transcription factor 2 (RUNX2), in colorectal cancer (CRC). MethodsMGP and RUNX2 expression were analyzed in cancer and non-tumor biopsies samples from 33 CRC patients and 9 healthy controls by RT-qPCR. Consequently, statistical analyses were performed to evaluate the clinical-pathological significance of MGP and RUNX2 in CRC. MGP protein was also detected by immunohistochemical analysis. ResultsShowed an overall overexpression of MGP in the tumor mucosa of patients at mRNA level when compared to adjacent normal mucosa and healthy control tissues. In addition, analysis of the expression of RUNX2 mRNA demonstrated an overexpression in CRC tissue samples and a positive correlation with MGP expression (Pearson correlation coefficient 0.636; p ≤ 0.01) in tumor mucosa. However correlations between MGP gene expression and clinical-pathological characteristics, such as gender, age and pathology classification did not provide relevant information that may shed light towards the differences of MGP expression observed between normal and malignant tissue. ConclusionsWe were able to associate the high levels of MGP mRNA expression with a worse prognosis and survival rate lower than five years.These results contributed to improve our understanding of the molecular mechanism underlying MGP deregulation in cancer.

The Role of Vitamin K and Its Related Compounds in Mendelian and Acquired Ectopic Mineralization Disorders.

Ectopic mineralization disorders comprise a broad spectrum of inherited or acquired diseases characterized by aberrant deposition of calcium crystals in multiple organs, such as the skin, eyes, kidneys, and blood vessels. Although the precise mechanisms leading to ectopic calcification are still incompletely known to date, various molecular targets leading to a disturbed balance between pro- and anti-mineralizing pathways have been identified in recent years. Vitamin K and its related compounds, mainly those post-translationally activated by vitamin K-dependent carboxylation, may play an important role in the pathogenesis of ectopic mineralization as has been demonstrated in studies on rare Mendelian diseases, but also on highly prevalent disorders, like vascular calcification. This narrative review compiles and summarizes the current knowledge regarding the role of vitamin K, its metabolism, and associated compounds in the pathophysiology of both monogenic ectopic mineralization disorders, like pseudoxanthoma elasticum or Keutel syndrome, as well as acquired multifactorial diseases, like chronic kidney disease. Clinical and molecular aspects of the various disorders are discussed according to the state-of-the-art, followed by a comprehensive literature review regarding the role of vitamin K in molecular pathophysiology and as a therapeutic target in both human and animal models of ectopic mineralization disorders.

A rare diagnosis: Keutel Syndrome

Tracheobronchial cartilage calcification is a rare finding in the pediatric population. Keutel syndrome (OMIM 245150) is a very rare syndrome characterized with diffuse calcification of cartilage, brachytelephalangia, pulmonary stenosis, midline defects, stippled epiphysis in infancy, and hearing loss accompanied by recurrent respiratory infections and asthma-like attacks. Here, we present a 14-year-old patient who was followed up with the diagnosis of asthma, but did not respond to appropriate asthma treatment. She was subsequently diagnosed as having Keutel syndrome with cartilage calcification on the tracheobranchial tree and auricula, atypical facial features, recurrent otitis media, hearing loss, and recurrent asthma-like symptoms.

Matrix Gla protein deficiency impairs nasal septum growth, causing midface hypoplasia

Genetic and environmental factors may lead to abnormal growth of the orofacial skeleton, affecting the overall structure of the face. In this study, we investigated the craniofacial abnormalities in a mouse model for Keutel syndrome, a rare genetic disease caused by loss-of-function mutations in the matrix Gla protein (MGP) gene. Keutel syndrome patients show diffuse ectopic calcification of cartilaginous tissues and impaired midface development. Our comparative cephalometric analyses of micro-computed tomography images revealed a severe midface hypoplasia in Mgp-/- mice. In vivo reporter studies demonstrated that the Mgp promoter is highly active at the cranial sutures, cranial base synchondroses, and nasal septum. Interestingly, the cranial sutures of the mutant mice showed normal anatomical features. Although we observed a mild increase in mineralization of the spheno-occipital synchondrosis, it did not reduce the relative length of the cranial base in comparison with total skull length. Contrary to this, we found the nasal septum to be abnormally mineralized and shortened in Mgp-/- mice. Transgenic restoration of Mgp expression in chondrocytes fully corrected the craniofacial anomalies caused by MGP deficiency, suggesting a local role for MGP in the developing nasal septum. Although there was no up-regulation of markers for hypertrophic chondrocytes, a TUNEL assay showed a marked increase in apoptotic chondrocytes in the calcified nasal septum. Transmission electron microscopy confirmed unusual mineral deposits in the septal extracellular matrix of the mutant mice. Of note, the systemic reduction of the inorganic phosphate level was sufficient to prevent abnormal mineralization of the nasal septum in Mgp-/-;Hyp compound mutants. Our work provides evidence that modulation of local and systemic factors regulating extracellular matrix mineralization can be possible therapeutic strategies to prevent ectopic cartilage calcification and some forms of congenital craniofacial anomalies in humans.

Inherited Arterial Calcification Syndromes: Etiologies and Treatment Concepts.

We give an update on the etiology and potential treatment options of rare inherited monogenic disorders associated with arterial calcification and calcific cardiac valve disease. Genetic studies of rare inherited syndromes have identified key regulators of ectopic calcification. Based on the pathogenic principles causing the diseases, these can be classified into three groups: (1) disorders of an increased extracellular inorganic phosphate/inorganic pyrophosphate ratio (generalized arterial calcification of infancy, pseudoxanthoma elasticum, arterial calcification and distal joint calcification, progeria, idiopathic basal ganglia calcification, and hyperphosphatemic familial tumoral calcinosis; (2) interferonopathies (Singleton-Merten syndrome); and (3) others, including Keutel syndrome and Gaucher disease type IIIC. Although some of the identified causative mechanisms are not easy to target for treatment, it has become clear that a disturbed serum phosphate/pyrophosphate ratio is a major force triggering arterial and cardiac valve calcification. Further studies will focus on targeting the phosphate/pyrophosphate ratio to effectively prevent and treat these calcific disease phenotypes.

Case report of Keutel syndrome in infancy

Case report of Keutel syndrome in infancy

Deeper understanding of carboxylase

In this issue of Blood, Tie et al report the development of a cleverly engineered, cell-based system for studying mutations in γ-glutamyl carboxylase (GGCX), the enzyme responsible for converting glutamate residues in certain proteins to γ-carboxyglutamate (Gla). They use this cell-based assay system to help explain the clinical manifestations of some otherwise puzzling GGCX gene mutations in humans that cause phenotypes ranging from severe bleeding to Keutel syndrome.

Characterization of vitamin K–dependent carboxylase mutations that cause bleeding and nonbleeding disorders

AbstractVitamin K–dependent coagulation factors deficiency is a bleeding disorder mainly associated with mutations in γ-glutamyl carboxylase (GGCX) that often has fatal outcomes. Some patients with nonbleeding syndromes linked to GGCX mutations, however, show no coagulation abnormalities. The correlation between GGCX genotypes and their clinical phenotypes has been previously unknown. Here we report the identification and characterization of novel GGCX mutations in a patient with both severe cerebral bleeding disorder and comorbid Keutel syndrome, a nonbleeding malady caused by functional defects of matrix γ-carboxyglutamate protein (MGP). To characterize GGCX mutants in a cellular milieu, we established a cell-based assay by stably expressing 2 reporter proteins (a chimeric coagulation factor and MGP) in HEK293 cells. The endogenous GGCX gene in these cells was knocked out by CRISPR-Cas9–mediated genome editing. Our results show that, compared with wild-type GGCX, the patient's GGCX D153G mutant significantly decreased coagulation factor carboxylation and abolished MGP carboxylation at the physiological concentration of vitamin K. Higher vitamin K concentrations can restore up to 60% of coagulation factor carboxylation but do not ameliorate MGP carboxylation. These results are consistent with the clinical results obtained from the patient treated with vitamin K, suggesting that the D153G alteration in GGCX is the causative mutation for both the bleeding and nonbleeding disorders in our patient. These findings provide the first evidence of a GGCX mutation resulting in 2 distinct clinical phenotypes; the established cell-based assay provides a powerful tool for studying the clinical consequences of naturally occurring GGCX mutations in vivo.

Petrified Ears or Calcified Pinnae

Clinical Image Calcification or ossification of the auricular cartilage is also known as ‘petrified ears.’ This condition was first described by Bochdalek in 1866. It is characterized by partial or total calcification or ossification of the external ear cartilage. The condition may be asymptomatic and picked up on clinical or radiological examination of the patient or it may be symptomatic resulting in discomfort due to stiffness or rigidity of ears. Rarely the overlying skin may show ulceration. A wide variety of causes for ear cartilage calcification have been reported. The process may involve one or both external ears with sparing of the ear lobes. The common causes include boxing, frostbite, trauma and gout. Many other uncommon conditions are associated with calcified pinnae and these include acromegaly, Addison disease, alkaptonuria, connective tissue diseases, calcium pyrophosphate deposition disease, Cushing’s syndrome, aging, hypercalcemic states, hyperparathyroidism, hypoparathyroidism, hypopituitarism, following infection or inflammation of external ear, Keutel syndrome, relapsing polychondritis, sarcoidosis and rarely syphilitic polychondritis. In a few cases no underlying cause can be established and in that situation the calcification of pinnae is considered as idiopathic. In the case presented here extensive calcification of bilateral external ear cartilage was noted incidentally during the CT study of cervical spine performed for symptoms of neck pain and stiffness. CT showed features of diffuse idiopathic skeletal hyperostosis with extensive ossification of anterior and posterior longitudinal ligaments of cervical spine in addition to heavily calcified ears.

Novel susceptability loci for osteoarthritis of the hand: Variants in coding EN GENE regulatory regions

Purpose: Osteoarthritis (OA) of the hand, is to a large extend, genetically determined. However, despite the large GWAS efforts into OA over the last years only one locus has been found to be associated to hand OA. We here aim to identify novel genes and pathways involved in the etiology of hand OA. Methods: We conducted a genome-wide association study of hand OA in a discovery set of 10,155 participants from the three Rotterdam Study cohorts (RS1, RS2 and RS3) using standardized age and gender adjustments. We have used a quantitative bilateral hand OA phenotype, summing all KL-scores of the hand joints for both hands (min score: 0, max score: 128). EasyQC was used to conduct quality control across cohorts. Results were combined in a jointed meta-analysis using inverse variance weighting. Genome-wide significant signals were analyzes for enrichment in genomic regulatory regions, using data from the ENCODE and Roadmap epigenetics project. Results: The discovery analysis yielded 16 loci with suggestive evidence for association (P<5*10-6 ) and another 3 loci with genome-wide significant association (p<5*10-8). These novel genome-wide significant loci include SNPs in or near the MGP, PTHLH and APBB2 genes. The risk alleles of MGP, PTHLH and APBB2 genes had a higher KL-sum score compared to the reference allele (delta KL-score was 7, 6, and 23 respectively) MGP codes for Matrix Gla Protein and is important for limiting calcification in tissues. Mutations in the MGP gene have been associated to Keutel Syndrome, which is characterized by abnormal mineralization of cartilage tissue. We here identified a SNP resulting in a protein-change to be associated with hand OA. The identified SNPs in the PTHLH-locus and the APBB2-locus co-localize with enhancer histone markers in osteoblast and chondrogenic cells from the Roadmap and ENCODE database, suggesting a potential gene regulatory function for these SNPs. Conclusions: We identified 3 loci to be associated to hand OA, a coding variant in the MPG gene and two intronic variants in APBB2 and CCDC91 located near gene regulatory marks specific for bone and/or cartilage. In addition, we have also found 16 loci suggestively associated to hand OA. Future analysis will consist of validation of our findings in other cohorts and further functional assessment and pathway analyses of the identified variants

Keutel syndrome: Augmentation of the nose with serial fat grafting.

Keutel syndrome: Augmentation of the nose with serial fat grafting.

From variome to phenome: Pathogenesis, diagnosis and management of ectopic mineralization disorders.

Ectopic mineralization - inappropriate biomineralization in soft tissues - is a frequent finding in physiological aging processes and several common disorders, which can be associated with significant morbidity and mortality. Further, pathologic mineralization is seen in several rare genetic disorders, which often present life-threatening phenotypes. These disorders are classified based on the mechanisms through which the mineralization occurs: metastatic or dystrophic calcification or ectopic ossification. Underlying mechanisms have been extensively studied, which resulted in several hypotheses regarding the etiology of mineralization in the extracellular matrix of soft tissue. These hypotheses include intracellular and extracellular mechanisms, such as the formation of matrix vesicles, aberrant osteogenic and chondrogenic signaling, apoptosis and oxidative stress. Though coherence between the different findings is not always clear, current insights have led to improvement of the diagnosis and management of ectopic mineralization patients, thus translating pathogenetic knowledge (variome) to the phenotype (phenome). In this review, we will focus on the clinical presentation, pathogenesis and management of primary genetic soft tissue mineralization disorders. As examples of dystrophic calcification disorders Pseudoxanthoma elasticum, Generalized arterial calcification of infancy, Keutel syndrome, Idiopathic basal ganglia calcification and Arterial calcification due to CD73 (NT5E) deficiency will be discussed. Hyperphosphatemic familial tumoral calcinosis will be reviewed as an example of mineralization disorders caused by metastatic calcification.

Keutel syndrome: Report of two novel MGP mutations and discussion of clinical overlap with arylsulfatase E deficiency and relapsing polychondritis

Keutel syndrome is a rare, autosomal recessive disorder characterized by diffuse cartilage calcification, peripheral pulmonary artery stenosis, midface retrusion, and short distal phalanges. To date, 28 patients from 18 families have been reported, and five mutations in the matrix Gla protein gene (MGP) have been identified. The matrix Gla protein (MGP) is a vitamin K-dependent extracellular protein that functions as a calcification inhibitor through incompletely understood mechanisms. We present the clinical manifestations of three affected siblings from a consanguineous Turkish family, in whom we detected the sixth MGP mutation (c.79G>T, which predicts p.E27X) and a fourth unrelated patient in whom we detected the seventh MGP mutation, a partial deletion of exon 4. Both mutations predict complete loss of MGP function. One of the patients presented initially with a working diagnosis of relapsing polychondritis. Clinical features suggestive of Keutel syndrome were also observed in one additional unrelated patient who was later found to have a deletion of arylsulfatase E, consistent with a diagnosis of X-linked recessive chondrodysplasia punctata. Through a discussion of these cases, we highlight the clinical overlap of Keutel syndrome, X-linked chondrodysplasia punctata, and the inflammatory disease relapsing polychondritis.

Neuroimaging findings in children with Keutel syndrome

Keutel syndrome is a rare autosomal-recessive condition characterized by abnormal cartilage calcification. Neuroimaging findings associated with this condition have been randomly described in the literature. To systematically evaluate the neuroimaging findings in a series of children with Keutel syndrome to broaden our base of knowledge. Four children with confirmed Keutel syndrome were reviewed for the brain, head and neck imaging findings. Three of the four children, all siblings, showed evidence of moyamoya syndrome. All four siblings had pinna cartilage calcification. We propose that Keutel syndrome be considered and included among the secondary causes of moyamoya syndrome. In children with petrified auricle and neurological symptoms, Keutel syndrome should be considered and brain MRI with MRA is required.