Fracture healing in a mouse model of Hajdu-Cheney-Syndrome with high turnover osteopenia results in decreased biomechanical stability.

Notch signaling regulates cell fate in multiple tissues including the skeleton. Hajdu-Cheney-Syndrome (HCS), caused by gain-of-function mutations in the Notch2 gene, is a rare inherited disease featuring early-onset osteoporosis and increased risk for fractures and non-union. As the impact of Notch2 overactivation on fracture healing is unknown, we studied bone regeneration in mice harboring a human HCS mutation. HCS mice, displaying high turnover osteopenia in the non-fractured skeleton, exhibited only minor morphologic alterations in the progression of bone regeneration, evidenced by static radiological and histological outcome measurements. Histomorphometry showed increased osteoclast parameters in the callus of HCS mice, which was accompanied by an increased expression of osteoclast and osteoblast markers. These observations were accompanied by inferior biomechanical stability of healed femora in HCS mice. Together, our data demonstrate that structural indices of bone regeneration are normal in HCS mice, which, however, exhibit signs of increased callus turnover and display impaired biomechanical stability of healed fractures.

Hajdu-Cheney Syndrome: A Systematic Review of the Literature.

Hajdu-Cheney syndrome (HCS) is a rare genetic disease that causes acroosteolysis and generalized osteoporosis, accompanied by a series of developmental skeletal disorders and multiple clinical and radiological manifestations. It has an autosomal dominant inheritance, although there are several sporadic non-hereditary cases. The gene that has been associated with Hajdu-Cheney syndrome is NOTCH2. The described phenotype and clinical signs and symptoms are many, varied, and evolve over time. As few as 50 cases of this disease, for which there is currently no curative treatment, have been reported to date. The main objective of this systematic review was to evaluate the results obtained in research regarding Hajdu-Cheney Syndrome. The findings are reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and were registered on the web PROSPERO under the registration number CRD42020164377. A bibliographic search was carried out using the online databases Orphanet, PubMed, and Scielo; articles from other open access sources were also considered. Finally, 76 articles were included, and after their analysis, we have obtained a series of hypotheses as results that will support further studies on this matter.

Antisense oligonucleotides targeting Notch2 ameliorate the osteopenic phenotype in a mouse model of Hajdu-Cheney syndrome.

Notch receptors play critical roles in cell-fate decisions and in the regulation of skeletal development and bone remodeling. Gain-of-function NOTCH2 mutations can cause Hajdu-Cheney syndrome, an untreatable disease characterized by osteoporosis and fractures, craniofacial developmental abnormalities, and acro-osteolysis. We have previously created a mouse model harboring a point 6955C→T mutation in the Notch2 locus upstream of the PEST domain, and we termed this model Notch2tm1.1Ecan Heterozygous Notch2tm1.1Ecan mutant mice exhibit severe cancellous and cortical bone osteopenia due to increased bone resorption. In this work, we demonstrate that the subcutaneous administration of Notch2 antisense oligonucleotides (ASO) down-regulates Notch2 and the Notch target genes Hes-related family basic helix-loop-helix transcription factor with YRPW motif 1 (Hey1), Hey2, and HeyL in skeletal tissue from Notch2tm1.1Ecan mice. Results of microcomputed tomography experiments indicated that the administration of Notch2 ASOs ameliorates the cancellous osteopenia of Notch2tm1.1Ecan mice, and bone histomorphometry analysis revealed decreased osteoclast numbers in Notch2 ASO-treated Notch2tm1.1Ecan mice. Notch2 ASOs decreased the induction of mRNA levels of TNF superfamily member 11 (Tnfsf11, encoding the osteoclastogenic protein RANKL) in cultured osteoblasts and osteocytes from Notch2tm1.1Ecan mice. Bone marrow-derived macrophage cultures from the Notch2tm1.1Ecan mice displayed enhanced osteoclastogenesis, which was suppressed by Notch2 ASOs. In conclusion, Notch2tm1.1Ecan mice exhibit cancellous bone osteopenia that can be ameliorated by systemic administration of Notch2 ASOs.

A novel mutation in the matrix metallopeptidase 2 coding gene associated with intrafamilial variability of multicentric osteolysis, nodulosis, and arthropathy.

BACKGROUND: MONA, which stands for a spectrum of Multicentric Osteolysis, subcutaneous Nodulosis, and Athropathia, is an ultra rare autosomal recessive disorder caused by mutations in the matrix metallopeptidase 2 (MMP2) gene. To date only 44 individuals, carrying 22 different mutations have been reported. Here we report on two brothers with identical homozygous MMP2 gene mutations, but with clearly different phenotypes. METHODS: Genomic DNA was isolated from the affected brothers and the parents. An iliac crest bone biopsy was taken from the younger patient (index case). The level of matrix metallopeptidase 2 enzyme (MMP2) in serum and synovial fluid of the younger patient was analyzed using gelatin zymography. RESULTS: The DNA analysis revealed a homozygous c.1188C>A transversion on exon 8 of the gene. The affected brothers had the same homozygous variant and the parents were heterozygous to this variant. This variant has been reported as a compound heterozygous mutation on one individual resulting in scleroderma like skin thickening. Bone histomorphometry indicated increased trabecular bone remodeling and turnover. The zymography revealed that the level of MMP2 was completely nonmeasurable in the serum and only a minor gelatinolytic protein band of about similar molecular weight as MMP2 was found in the synovial fluid. CONCLUSIONS: Both the age at the onset and the phenotypic severity of the syndrome in these two brothers were different despite identical genotypes. The younger patients had corneal opacities leading to deteriorating visual acuity. For the first time in this disease, opacities were successfully treated with corneal transplantations.

Phenotype variability in Hajdu-Cheney syndrome.

Hajdu Cheney syndrome is a rare autosomal dominant skeletal dysplasia, with multi-organ involvement, caused by pathogenic variants in NOTCH2. It is characterized by progressive focal bone destruction, including acro-osteolysis and generalized osteoporosis, craniofacial anomalies, hearing loss, cardiovascular involvement and polycystic kidneys. Distinct radiographic findings, such as a serpentine fibula, may aid in facilitating the diagnosis. Despite several dozens of cases described in the literature, diagnosis often remains elusive, resulting in many cases in a delay in diagnosis reaching adolescence or adulthood. We report herein two unrelated patients of Turkish/Lebanese Jewish and Ashkenazi Jewish descent, each presenting with distinct clinical challenges and subsequently distinct diagnostic odysseys leading to their molecular diagnosis. These illustrative clinical descriptions underscore the wide phenotypic variability of HCS, and further contribute to the current knowledge regarding this rare entity.

Notch signaling suppresses glucose metabolism in mesenchymal progenitors to restrict osteoblast differentiation.

Notch signaling critically controls cell fate decisions in mammals, both during embryogenesis and in adults. In the skeleton, Notch suppresses osteoblast differentiation and sustains bone marrow mesenchymal progenitors during postnatal life. Stabilizing mutations of Notch2 cause Hajdu-Cheney syndrome, which is characterized by early-onset osteoporosis in humans, but the mechanism whereby Notch inhibits bone accretion is not fully understood. Here, we report that activation of Notch signaling by either Jagged1 or the Notch2 intracellular domain suppresses glucose metabolism and osteoblast differentiation in primary cultures of bone marrow mesenchymal progenitors. Importantly, deletion of Notch2 in the limb mesenchyme increases both glycolysis and bone formation in the long bones of postnatal mice, whereas pharmacological reduction of glycolysis abrogates excessive bone formation. Mechanistically, Notch reduces the expression of glycolytic and mitochondrial complex I genes, resulting in a decrease in mitochondrial respiration, superoxide production, and AMPK activity. Forced activation of AMPK restores glycolysis in the face of Notch signaling. Thus, suppression of glucose metabolism contributes to the mechanism, whereby Notch restricts osteoblastogenesis from bone marrow mesenchymal progenitors.

Induction of the Hajdu-Cheney Syndrome Mutation in CD19 B Cells in Mice Alters B-Cell Allocation but Not Skeletal Homeostasis.

Mice harboring Notch2 mutations replicating Hajdu-Cheney syndrome (Notch2tm1.1ECan) have osteopenia and exhibit an increase in splenic marginal zone B cells with a decrease in follicular B cells. Whether the altered B-cell allocation is responsible for the osteopenia of Notch2tm1.1ECan mutants is unknown. To determine the effect of NOTCH2 activation in B cells on splenic B-cell allocation and skeletal phenotype, a conditional-by-inversion (COIN) Hajdu-Cheney syndrome allele of Notch2 (Notch2[ΔPEST]COIN) was used. Cre recombination generates a permanent Notch2ΔPEST allele expressing a transcript for which sequences coding for the proline, glutamic acid, serine, and threonine-rich (PEST) domain are replaced by a stop codon. CD19-Cre drivers were backcrossed into Notch2[ΔPEST]COIN/[ΔPEST]COIN to generate CD19-specific Notch2ΔPEST/ΔPEST mutants and control Notch2[ΔPEST]COIN/[ΔPEST]COIN littermates. There was an increase in marginal zone B cells and a decrease in follicular B cells in the spleen of CD19Cre/WT;Notch2ΔPEST/ΔPEST mice, recapitulating the splenic phenotype of Notch2tm1.1ECan mice. The effect was reproduced when the NOTCH1 intracellular domain was induced in CD19-expressing cells (CD19Cre/WT;RosaNotch1/WT mice). However, neither CD19Cre/WT;Notch2ΔPEST/ΔPEST nor CD19Cre/WT;RosaNotch1/WT mice had a skeletal phenotype. Moreover, splenectomies in Notch2tm1.1ECan mice did not reverse their osteopenic phenotype. In conclusion, Notch2 activation in CD19-expressing cells determines B-cell allocation in the spleen but has no skeletal consequences.

The Age Dependent Progression of Hajdu-Cheney Syndrome in Two Families.

Hajdu-Cheney syndrome (HCS) is a rare multi-system disease with autosomal dominant inheritance and skeletal involvement, resulting mostly in craniofacial dysmorphy with mid-face hypoplasia, dental anomalies, short stature, scoliosis, shortening of the digits and nail beds, acro-osteolysis and osteoporosis. We report the progression of clinical and radiographic findings in five patients with Hajdu-Cheney syndrome from two families. A custom capture array designed to capture exons and adjacent intron sequences of 230 selected genes were used for molecular analyses, and the pathogenic variants identified were confirmed by PCR and Sanger sequencing. In both families we observed age-dependent changes in the disease, with a progression of pain in older patients, a shortening of digits and nail beds on both the hands and feet, kyphoscoliosis and the persistence of Wormian bones in lambdoid sutures. Molecular analyses performed in two patients revealed that they are heterozygotes for a c.6255T>A (p.Cys2085*) variant in the NOTCH2 gene, resulting in a premature stop-codon. Bone mineral density (Z-score < -2) did not improved in a girl treated with calcium and vitamin D supplementation during childhood and bisphosphonate during adolescence. Hajdu-Cheney syndrome is a slowly progressive disease with a frequently unfavourable prognosis in elderly patients, especially for the development of dental anomalies, osteoporosis and the progression of skeletal complications requiring orthopedic surgeries.

Sustained Notch2 signaling in osteoblasts, but not in osteoclasts, is linked to osteopenia in a mouse model of Hajdu-Cheney syndrome.

Individuals with Hajdu-Cheney syndrome (HCS) present with osteoporosis, and HCS is associated with NOTCH2 mutations causing deletions of the proline-, glutamic acid-, serine-, and threonine-rich (PEST) domain that are predicted to enhance NOTCH2 stability and cause gain-of-function. Previously, we demonstrated that mice harboring Notch2 mutations analogous to those in HCS (Notch2HCS) are severely osteopenic because of enhanced bone resorption. We attributed this phenotype to osteoclastic sensitization to the receptor activator of nuclear factor-κB ligand and increased osteoblastic tumor necrosis factor superfamily member 11 (Tnfsf11) expression. Here, to determine the individual contributions of osteoclasts and osteoblasts to HCS osteopenia, we created a conditional-by-inversion (Notch2COIN ) model in which Cre recombination generates a Notch2ΔPEST allele expressing a Notch2 mutant lacking the PEST domain. Germ line Notch2COIN inversion phenocopied the Notch2HCS mutant, validating the model. To activate Notch2 in osteoclasts or osteoblasts, Notch2COIN mice were bred with mice expressing Cre from the Lyz2 or the BGLAP promoter, respectively. These crosses created experimental mice harboring a Notch2ΔPEST allele in Cre-expressing cells and control littermates expressing a wild-type Notch2 transcript. Notch2COIN inversion in Lyz2-expressing cells had no skeletal consequences and did not affect the capacity of bone marrow macrophages to form osteoclasts in vitro In contrast, Notch2COIN inversion in osteoblasts led to generalized osteopenia associated with enhanced bone resorption in the cancellous bone compartment and with suppressed endocortical mineral apposition rate. Accordingly, Notch2 activation in osteoblast-enriched cultures from Notch2COIN mice induced Tnfsf11 expression. In conclusion, introduction of the HCS mutation in osteoblasts, but not in osteoclasts, causes osteopenia.

A novel NOTCH2 mutation identified in a Korean family with Hajdu-Cheney syndrome showing phenotypic diversity.

Hajdu-Cheney syndrome (HCS) and serpentine fibula-polycystic kidney syndrome (SFPKS) share many similarities, including craniofacial abnormalities, bony deformities, and renal involvement. Because mutations in exon 34 of NOTCH2 have been identified recently in both HCS and SFPKS patients, it has been suggested that these two syndromes be classed as the same disorder. A 3-year-old boy presented with polycystic kidneys and club feet detected during the fetal period; however, acroosteolysis and curved fibulae were not observed. His mother showed osteoporosis and had a history of compression fractures in the spine without renal anomalies. Although the same novel mutation in NOTCH2 was found in both the mother and her son, these patients displayed different clinical manifestations. In this report, we present a familial case of HCS in a boy and his mother that was suspected on physical examination and radiological findings. We speculate that HCS and SFPKS are a single disease entity with a wide spectrum of clinical manifestations associated with truncating mutations in exon 34 of NOTCH2.

A new acro-osteolysis syndrome caused by duplications including PTHLH.

Parathyroid hormone-like hormone (PTHLH, MIM 168470) is a humoral factor, structurally and functionally related to parathyroid hormone, which mediates multiple effects on chondrocyte, osteoblast and osteoclast function. Mutations and copy number imbalances of the PTHLH locus and in the gene encoding its receptor, PTHR1, result in a variety of skeletal dysplasias including brachydactyly type E, Eiken syndrome, Jansen metaphyseal chondrodysplasia and Blomstrand type chondrodysplasia. Here we describe three individuals with duplications of the PTHLH locus, including two who are mosaic for these imbalances, leading to a hitherto unrecognized syndrome characterized by acro-osteolysis, cortical irregularity of long bones and metadiaphyseal enchondromata.

Prenatal and postnatal findings in serpentine fibula polycystic kidney syndrome and a review of the NOTCH2 spectrum disorders.

Serpentine fibula polycystic kidney syndrome (SFPKS; OMIM600330) is a rare skeletal dysplasia with a characteristic phenotype that includes polycystic kidneys, S-shaped fibulas, and abnormal craniofacial features. SFPKS shares features with Alagille (AGS; OMIM) and Hajdu-Cheney (HCS; OMIM10250) syndromes. All three syndromes result from mutations in the gene that encodes NOTCH2, one of the receptors involved in Notch signaling. Notch signaling is a major developmental signaling pathway, as well as a key regulator of numerous cellular processes. In this report, we present the prenatal ultrasound and postnatal findings in a 23-week fetus with severe manifestations of SPKS and heterozygosity for a de novo mutation in exon 34 of NOTCH2. These findings expand the phenotypic spectrum of NOTCH2 mutations and demonstrate the findings in the prenatal period.

Mutations in NOTCH2 in patients with Hajdu-Cheney syndrome.

UNLABELLED: The Hajdu-Cheney syndrome is a very rare disease that affects several organ system, leading to severe osteoporosis and other abnormalities. We describe clinical and genetic findings of nine patients with this disease. INTRODUCTION: The Hajdu-Cheney syndrome (HCS) is a rare autosomal dominant disorder characterized by severe osteoporosis, acroosteolysis of the distal phalanges, renal cysts, and other abnormalities. Recently, heterozygous mutations in NOTCH2 were identified as the cause of HCS. METHODS: Nine patients with typical presentations of HCS took part in this study: five affected patients from two small families and four sporadic cases. Peripheral blood DNA was obtained and exome sequencing performed in one affected individual per family and in all four sporadic cases. Sanger sequencing confirmed mutations in all patients. RESULTS: One of the identified mutations was introduced in a plasmid encoding NOTCH2. Wild-type and mutant NOTCH2 were transiently expressed in HEK293 cells to assess intracellular localization after ligand activation. Deleterious heterozygous mutations in the last NOTCH2 exon were identified in all patients; five of the six mutations were novel. CONCLUSION: Consistent with previous reports, all mutations are predicted to result in a loss of the proline/glutamic acid/serine/threonine sequence, which harbors signals for degradation, therefore suggesting activating mutations. One of the six mutations furthermore predicted disruption of the second nuclear localization signal of NOTCH2, but the mutant revealed normal nuclear localization after transfection, which is consistent with the proposed gain-of-function mechanism as the cause of this autosomal dominant disease. Our findings confirm that heterozygous NOTCH2 mutations are the cause of HCS and expand the mutational spectrum of this disorder.

Two-year cyclic infusion of pamidronate improves bone mass density and eliminates risk of fractures in a girl with osteoporosis due to Hajdu-Cheney syndrome.

Hajdu-Cheney syndrome (HCS) is a rare disorder principally characterized by acro-osteolysis, distinctive craniofacial and skull changes, dental anomalies and short stature. A common finding in HCS patients is secondary osteoporosis that progresses over time and contributes to various skeletal problems, especially fractures. Although autosomal dominant inheritance has been documented in several families, sporadic (non-familial) cases have also been reported. Here, a case of a 9-year-old girl with familial HCS and multiple spinal fractures, who has been effectively treated with pamidronate, is presented. This is the first report of a beneficial effect of intravenous bisphosphonate administration on a child with HCS-related osteoporosis.

Serpentine fibula-polycystic kidney syndrome caused by truncating mutations in NOTCH2.

Serpentine fibula-polycystic kidney syndrome (SFPKS) is a rare disorder characterized by the association of craniofacial anomalies, radiological findings (wormian bones, elongated and bowed fibulae), polycystic kidneys, and normal intelligence. SFPKS shares many similarities with Hajdu-Cheney syndrome (HCS). We and others recently showed that truncating mutations in the last exon of NOTCH2 cause HCS. Here, we identify by Sanger sequencing two different heterozygous truncating mutations in the last exon of NOTCH2 in two unrelated patients with SFPKS. In one family, we show that the mutation occurred de novo. These findings demonstrate that SFPKS and HCS are both conditions caused by NOTCH2 mutations.

Mutations in NOTCH2 cause Hajdu-Cheney syndrome, a disorder of severe and progressive bone loss.

We used an exome-sequencing strategy and identified an allelic series of NOTCH2 mutations in Hajdu-Cheney syndrome, an autosomal dominant multisystem disorder characterized by severe and progressive bone loss. The Hajdu-Cheney syndrome mutations are predicted to lead to the premature truncation of NOTCH2 with either disruption or loss of the C-terminal proline-glutamate-serine-threonine-rich proteolytic recognition sequence, the absence of which has previously been shown to increase Notch signaling.

Truncating mutations in the last exon of NOTCH2 cause a rare skeletal disorder with osteoporosis.

Hajdu-Cheney syndrome is a rare autosomal dominant skeletal disorder with facial anomalies, osteoporosis and acro-osteolysis. We sequenced the exomes of six unrelated individuals with this syndrome and identified heterozygous nonsense and frameshift mutations in NOTCH2 in five of them. All mutations cluster to the last coding exon of the gene, suggesting that the mutant mRNA products escape nonsense-mediated decay and that the resulting truncated NOTCH2 proteins act in a gain-of-function manner.

Syndrome of Hajdu-Cheney: three case reports of orofacial interest.

Hajdu-Cheney syndrome is a rare, probably autosomal dominant connective tissue disorder with a variable expressivity. It is characterized by an osteoporotic skeleton, acro-osteolysis, a proportionate short stature, and distinctive orofacial anomalies. The aim of this article is to focus on the orofacial manifestations in two sporadic cases and one familial case with Hajdu-Cheney syndrome. Several common dental and craniofacial features are described. In contrast to earlier proposed diagnostic features, these patients show persisting deciduous teeth, problematic tooth eruption, and tendency toward a Class III malocclusion.