Hajdu-Cheney syndrome: a review

Elucidating the Molecular Landscape of Cystic Kidney Disease: Old Friends, New Friends and Some Surprises

Cystic kidney diseases (CyKD) are a diverse group of disorders affecting more than 1 in 1000 individuals. Over 120 genes are implicated, primarily encoding components of the primary cilium, transcription factors, and morphogens. Prognosis varies greatly by molecular diagnosis. Causal variants are not identified in 10%-60% of individuals due to our limited understanding of CyKD. To elucidate the molecular landscape of CyKD, we queried the CAG Biobank using the ICD10 codes N28.1, Q61.1, Q61.11, Q61.19, Q61.2, Q61.3, and Q61.8 to identify individuals with CyKD. One hundred eight individuals met clinical criteria for CyKD and underwent proband-only exome sequencing. Causal variants were identified in 86/108 (80%) individuals. The most common molecular diagnoses were PKD1-related autosomal dominant polycystic kidney disease (32/108; 30%) and autosomal recessive polycystic kidney disease (21/108; 19%). Other common molecular diagnoses were ciliopathy syndromes (7/108; 6.5%) and Tuberous Sclerosis (6/108; 5.6%). Seven individuals had variants in genes not previously associated with CyKD (7/108; 6.5%). Candidate genes were identified in five individuals (5/108; 4.5%). Discordance between molecular and clinical diagnosis was present in two individuals. We demonstrate a high molecular diagnosis rate in individuals with CyKD that can result in diagnostic reclassification, supporting a role for genetic testing in CyKD.

Molecular Mechanism of Notch Signaling and Macrophages in Deep Vein Thrombosis: A Comprehensive Review

Deep vein thrombosis is an acute medical condition, and the molecular basis of this etiology will be crucial in the discovery of more advanced therapies. This review has focused at the Notch signaling pathway, which plays a significant role in different physiological activities such as homeostasis, development, and disease. Also, reveal macrophage function in inflammation and thrombosis in depth, with a focus on their polarization and interaction with the endothelium during thrombosis. In this context, some essential cellular and molecular mechanisms relevant to thrombus pathogenesis, DVT aetiology and risk factors, as well as elements and composition of the Notch pathway, are covered in the end, with a focus on elements that distinguish canonical from non-canonical signaling pathways and their biological relevance to macrophages. Notch signaling has been shown to influence macrophage activation and polarization, influencing their function in thrombosis breakdown and resolution. This interplay between Notch signaling and macrophages may reveal possible treatment targets for DVT. Discuss the physiological role of Notch signaling in vascular biology, as well as how it contributes to thrombosis. The difficulties in implementing these discoveries in clinical practice are discussed, along with the status of ongoing clinical trials and experimental investigations focussing on macrophage-directed treatments and Notch inhibitors. These molecular insights synthesis provides a basis for the creation of novel strategies for the efficient management of DVT.

Root resorptions induced by genetic disorders: A systematic review

OBJECTIVES

Root resorption in permanent teeth is a common pathological process that often follows dental trauma or orthodontic treatment. More rarely, root resorption is a feature of genetic disorders and can help with diagnosis. Thus, the present review aims to determine which genetic disorders could induce pathological root resorptions and thus which mutated genes could be associated with them.

METHODS

We conducted a systematic review following the PRISMA guidelines. Articles describing root resorptions in patients with genetic disorders were included from PubMed, Embase, Web of Science, and Google Scholar. We synthesized the genetic disorder, the type, severity, and extent of the resorptions, as well as the other systemic and oral symptoms and histological features.

RESULTS

The synthetic analysis included 25 studies among 937 identified records. We analyzed 21 case reports, three case series, and one cohort study. Overall, we highlighted 14 different pathologies with described root resorptions. Depending on the pathology, the sites of resorption, their extent, and their severity showed differences.

CONCLUSION

With 14 genetic pathologies suspected to induce root resorptions, our findings are significant and enrich a previous classification. Among them, three metabolic disorders, three calcium-phosphorus metabolism disorders, and osteolysis disorders were identified.

First case of Hajdu-Cheney syndrome in Lithuania caused by novel NOTCH2 gene likely pathogenic variant

Hajdu-Cheney syndrome (HCS) is an extremely rare autosomal dominant skeletal disorder. The prevalence rate of less than 1 case per 1,000,000 newborns and only 50 cases were reported in the medical literature. HCS is characterized by progressive bone resorption in the distal phalanges (acro-osteolysis), progressive osteoporosis, distinct craniofacial changes, dental anomalies, and occasional association with renal abnormalities. HCS is caused by pathogenic variants in the NOTCH2 gene, 34th exon. We report first familial case of HCS caused by likely pathogenic variant of NOTCH2 gene c.6449delC, p.(Pro2150LeufsTer5).

Clinical and Genetic Correlation in Neurocristopathies: Bridging a Precision Medicine Gap

Neurocristopathies (NCPs) encompass a spectrum of disorders arising from issues during the formation and migration of neural crest cells (NCCs). NCCs undergo epithelial-mesenchymal transition (EMT) and upon key developmental gene deregulation, fetuses and neonates are prone to exhibit diverse manifestations depending on the affected area. These conditions are generally rare and often have a genetic basis, with many following Mendelian inheritance patterns, thus making them perfect candidates for precision medicine. Examples include cranial NCPs, like Goldenhar syndrome and Axenfeld-Rieger syndrome; cardiac-vagal NCPs, such as DiGeorge syndrome; truncal NCPs, like congenital central hypoventilation syndrome and Waardenburg syndrome; and enteric NCPs, such as Hirschsprung disease. Additionally, NCCs' migratory and differentiating nature makes their derivatives prone to tumors, with various cancer types categorized based on their NCC origin. Representative examples include schwannomas and pheochromocytomas. This review summarizes current knowledge of diseases arising from defects in NCCs' specification and highlights the potential of precision medicine to remedy a clinical phenotype by targeting the genotype, particularly important given that those affected are primarily infants and young children.

Severe Acro-osteolysis Mimicking Arthritis Mutilans in a Patient with Primary Hyperparathyroidism: A Case Report

BACKGROUND

Primary hyperparathyroidism (PHPT) should be considered in the differential diagnosis of a patient with suspected secondary osteoporosis, and severe osteoporosis with multiple fractures is frequently the first clinical manifestation of the disease.

CASE PRESENTATION

Mutilating arthritis (arthritis mutilans) can be part of the clinical presentation of a number of rheumatic diseases, most commonly seen in psoriatic arthritis, rheumatoid arthritis, and juvenile idiopathic arthritis, but also in systemic lupus, systemic sclerosis, and multicentric reticulohistiocytosis. Evidence exists that subperiosteal and subchondral bone resorption, seen in PHPT, could induce the so-called 'osteogenic synovitis', which could eventually lead to the development of a secondary osteoarthritis with bone deformities.

CONCLUSION

Here, we present a case report of a patient initially diagnosed with PHPT who presented with mutilating arthritis of the finger joints and discuss whether the severe acro-osteolysis is a manifestation of the endocrinopathy or whether there is a co-existing undiagnosed inflammatory joint disease.

Cranial vault suspension for basilar invagination in patients with open cranial sutures: technique and long-term follow-up. Illustrative case

BACKGROUND

Hajdu-Cheney syndrome (HCS) is an extremely rare genetic disorder characterized by severe osteoporosis, scoliosis, and persistent open cranial sutures (POCSs). Neurological complications include hydrocephalus, Chiari I malformations, and basilar invagination (BI). Surgical intervention in HCS is challenging due to severe osteoporosis, ligamentous laxity, POCSs, and extreme skeletal deformities. Herein, the authors present a case of BI repair in a patient with HCS and POCSs, requiring a novel technique of cranial vault suspension, with long-term follow-up.

OBSERVATIONS

A 20-year-old female with HCS and progressive symptomatic BI, initially managed with posterior fossa decompression and occipital to cervical fusion, subsequently required cranial vault expansion due to symptomatic shifting of her cranium secondary to POCS. This custom construct provided long-term stabilization and neurological improvement over a follow-up duration of 9.5 years. A literature review performed revealed three other cases of surgical intervention for BI in patients with HCS and clinicopathological characteristics of each case was compared to the present illustrative case.

LESSONS

POCSs in patients with BI complicate traditional surgical approaches, necessitating more invasive techniques to secure all mobile cranial parts for optimal outcomes. Using this cranial vault suspension and fusion technique results in lasting neurological improvement and construct stability.

Acroosteolysis and facial dysmorphia: a new case of Hajdu-Cheney syndrome

Hajdu-Cheney syndrome or acro-dento-osteo-dysplasia syndrome is a rare disease characterized by band osteolysis of distal phalanges and facial dysmorphia, among other manifestations. We present the case of a 45-year-old male who consulted for mechanical joint pain of both hands, facial dysmorphism, cranio-facial alterations, and digital telescoping with acroosteolysis.

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.

NOTCH2 related disorders: Description and review of the fetal presentation

Signs of skeletal dysplasias are relatively common in fetuses with abnormal ultrasound (US) findings. The diversity of congenital skeletal disorders, the possibility of late-onset severe phenotypes and overlapping syndromes can be a challenge in the way of diagnosis, even if prenatal high-throuput sequencing allows for a better diagnosis, prognosis and genetic counseling. Hajdu-Cheney spectrum pathologies are rarely described in prenatal, and the signs associated remain poorly known, and do not include specific postnatal signs as acro-osteolysis and premature osteoporosis. We hereby report a couple for whom a medical termination of pregnancy was performed because a severe polymalformative syndrome associating severely short limbs with bowed long bones, severe cardiopathy, hyperechogenic kidneys and dysmorphism. After fetopathological and radiological examinations, Exome Sequencing (ES) was performed and revealed a de novo truncating mutation in the last exon of NOTCH2, responsible for Hajdu-Cheney or Serpentine Fibula Polycystic Kidney syndromes.

Exploratory use of romosozumab for osteoporosis in a patient with Hajdu-Cheney syndrome: a case report

Hajdu-Cheney syndrome (HCS) is an inherited skeletal disorder caused by mutations in the Notch homolog protein 2 gene (NOTCH2). Treatment of this rare disease is challenging because there are no established guidelines worldwide. Previous case reports using bisphosphonates, denosumab, or teriparatide suggested that curative treatment for HCS did not exist yet in terms of preventing the disease progression. Therefore, the efficacy of romosozumab for osteoporosis in patients with HCS needs to be evaluated. Herein, we report the case of a 43-year-old woman who had progressive acro-osteolysis and repeated fractures since the age of 29 years. Next-generation sequencing confirmed HCS with a mutation at nucleotide 6758G>A, leading to Trp2253Ter replacement in NOTCH2. Romosozumab treatment was initiated because she had already received bisphosphonate for more than 10 years at other hospitals. After 1 year of romosozumab treatment, the bone mineral density (BMD) increased by 10.2%, 6.3%, and 1.3%, with Z scores of -2.9, -1.6, and -1.2 at the lumbar spine, femoral neck, and total hip, respectively. In addition, C-telopeptide was suppressed by 26.4% (0.121 to 0.089 ng/mL), and procollagen type I N-terminal propeptide increased by 18.7% (25.2 to 29.9 ng/mL). This was the first report of romosozumab treatment in patient with osteoporosis and HCS in Korea. One year of romosozumab treatment provided substantial gains in BMD with maintaining the last acro-osteolytic status without deteriorating, representing a possible treatment option for HCS.

Progress and Current Status in Hajdu-Cheney Syndrome with Focus on Novel Genetic Research

Hajdu-Cheney syndrome (HCS) is a rare autosomal dominant manifestation of a congenital genetic disorder caused by a mutation in the NOTCH2 gene. NOTCH signaling has variations from NOTCH 1 to 4 and maintains homeostasis by determining and regulating the proliferation and differentiation of various cells. In HCS, the over-accumulated NOTCH2 causes abnormal bone resorption due to its continuous excessive signaling. HCS is characterized by progressive bone destruction, has complex wide-range clinical manifestations, and significantly impacts the patient’s quality of life. However, no effective treatment has been established for HCS to date. There are genetic variants of NOTCH2 that have been reported in the ClinVar database of the U.S. National Institutes of Health. In total, 26 mutant variants were detected based on the American College of Medical Genetics and Genomics (ACMC). To date, there has been no comprehensive compilation of HCS mutations. In this review, we provide the most comprehensive list possible of HCS variants, nucleotide changes, amino acid definitions, and molecular consequences reported to date, following the ACMC guidelines.

Defining pathogenicity of NOTCH2 variants for diagnosis of Alagille syndrome type 2 using a large cohort of patients

BACKGROUND AND AIMS

Alagille syndrome (ALGS) type 2 caused by mutations in NOTCH2 has genotypic and phenotypic heterogeneity. Diagnosis in some atypical patients with isolated hepatic presentation could be missed.

METHODS

Using 2087 patients with paediatric liver manifestations, NOTCH2 allele frequencies, in-silico prediction, protein domains and clinical features were analysed to define the pathogenicity of NOTCH2 variants for diagnosis of ALGS type 2.

RESULTS

Among 2087 patients with paediatric liver manifestations, significantly more NOTCH2 variants were absent in gnomAD in patients with elevated γ-glutamyltransferase (GGT) (p = .041). Significantly more NOTCH2 variants which were absent in gnomAD were located in protein functional domains (p = .038). When missense variants were absent in gnomAD and predicted to be pathogenic by at least three out of seven in-silico tools, they were found to be significantly associated with liver manifestations with elevated GGT (p = .003). Comparing this to patients with likely benign (LB) variants, the patients with likely-pathogenic (LP) variants have significantly more liver manifestations with elevated GGT (p = .0001). Significantly more patients with LP variants had extra-hepatic phenotypes of ALGS compared with those patients with LB variants (p = .0004).

CONCLUSION

When NOTCH2 variants are absent in gnomAD, null variants and missense variants which were predicted to be pathogenic by at least three in-silico tools could be considered pathogenic in patients with high GGT chronic liver diseases.

Novel phenotypic feature in a patient with a recurrent NOTCH2 nonsense mutation

Pathogenic variants in NOTCH2 which encodes a single-pass transmembrane protein have been identified as a cause of several autosomal dominant congenital disorders. In particular, truncating mutations in exon 34 have been found in patients with skeletal abnormalities and dysmorphic features. We describe a patient with a de novo variant in NOTCH2 who displayed features of both Hajdu-Cheney syndrome (HJCYS) and serpentine fibula-polycystic kidney syndrome (SFPKS). The recurrent nonsense variant in exon 34 has been reported in seven other patients with syndromic presentations, making it the most common pathogenic variant for NOTCH2 in congenital disorders. In addition to the core features of HJCYS and SFPKS, there was a gastrointestinal tract malformation of an imperforate anus which has not been reported in patients with pathogenic variants in NOTCH2.

Advancing human disease research with fish evolutionary mutant models

Model organism research is essential to understand disease mechanisms. However, laboratory-induced genetic models can lack genetic variation and often fail to mimic the spectrum of disease severity. Evolutionary mutant models (EMMs) are species with evolved phenotypes that mimic human disease. EMMs complement traditional laboratory models by providing unique avenues to study gene-by-environment interactions, modular mutations in noncoding regions, and their evolved compensations. EMMs have improved our understanding of complex diseases, including cancer, diabetes, and aging, and illuminated mechanisms in many organs. Rapid advancements of sequencing and genome-editing technologies have catapulted the utility of EMMs, particularly in fish. Fish are the most diverse group of vertebrates, exhibiting a kaleidoscope of specialized phenotypes, many that would be pathogenic in humans but are adaptive in the species' specialized habitat. Importantly, evolved compensations can suggest avenues for novel disease therapies. This review summarizes current research using fish EMMs to advance our understanding of human disease.

Craniospinal Surgery in Hajdu-Cheney Syndrome: A Review of Case Reports

Hajdu-Cheney syndrome (HCS) is a rare metabolic bone disorder that results in severe osteoporosis and various skeletal deformities. Craniospinal pathology is commonly associated with it, but surgical management is challenging due to the distorted anatomy, reduced bone strength, and fusion failure due to osteolysis. Hence, the surgical difficulty in these patients requires careful consideration. In this study, we systematically review all published operative cases and complications to provide a comprehensive review pertaining to the spine and/or cranium in patients with HCS. By highlighting these cases and their associated complications, we aim to prepare practitioners who treat this difficult pathology.

Hajdu Cheney syndrome; A novel NOTCH2 mutation in a Syrian child, and treatment with zolidronic acid: A case report and a literature review of treatments

INTRODUCTION

Hajdu Cheney Syndrome (HCS) is a rare genetic disorder characterized by skeletal deformities such as acroosteolysis, osteoporosis, unique craniofacial features, and other systemic abnormalities. This syndrome is caused by NOTCH2 gene mutations, which cause an increase of osteoclast and osteoblast activity that leads to the increased bone resorption. Because of how rare the syndrome is and the vague onset of the symptoms, it can be challenging to make an early diagnosis.

CASE PRESENTATION

We report a case of a female child with HCS who has a new NOTCH2 mutation sequence; (NM_024408.3:c.6463G > T) protein change (Glu2155*), and to our knowledge this is the first reported and diagnosed case in Syria. She presents with short stature, unique craniofacial features, scoliosis, kyphosis, and signs of osteoporosis, in addition to Patent Ductus Arteriosus. The patient was diagnosed with Hajdu Cheney Syndrome, and administered zolidronic acid, and she responded well to the treatment; showing signs of improved bone density and improvement in height, where her bone density improved from 0.23 to 0.31, and she gained 11 cm in height after the treatment.

CONCLUSION

Due to the rarity of the syndrome, there is no established guideline for treatment yet. Based on the pathophysiology of the syndrome that causes increased bone resorption, treatment with the Bisphosphonates group has yielded positive outcomes. Furthermore, we compare different treatments in the literature with their results.

Operative Management of Spinal Deformity Secondary to Hajdu-Cheney Syndrome

Hajdu-Cheney syndrome (HCS) is an exceedingly rare disease with fewer than 100 cases described in the medical literature. It is most strongly associated with a defect in the transmembrane protein NOTCH2. Though the exact mechanism in humans is not yet known, the defect results in various skeletal abnormalities including severe osteoporosis placing these patients at high risk for progressive spinal deformity. Due to various common syndromic features including ligamentous laxity, increased osteoclast activity, skeletal malformations, patency of cranial sutures, and the aforementioned severe osteoporosis, these patients require special consideration from treating surgeons. There are currently only nine reported cases of spinal surgery in HCS patients. Herein, we describe the cases of two patients with HCS requiring surgery for progressive spinal deformity. Six months following surgery, both patients reported excellent outcomes with significant improvement in symptoms.

Skeletal characterization in a patient with Hajdu-Cheney syndrome undergoing total knee arthroplasty

Hajdu-Cheney syndrome (HCS) is a rare genetic connective tissue disorder caused by gain-of-function mutations in the NOTCH2 gene. We report a 38-year-old male HCS patient with a history of multiple pathologic fractures, poor bone stock under intermittent antiresorptive therapy, and secondary osteoarthritis (OA) of the knee, in which we successfully performed total knee arthroplasty (TKA). Next to a detailed skeletal assessment including laboratory bone metabolism markers, dual energy X-ray absorptiometry (DXA), and high-resolution peripheral quantitative computed tomography (HR-pQCT), undecalcified histologic and histomorphometric analysis was performed on intraoperatively obtained tibial cut sections. This multiscale assessment revealed a severe, combined trabecular-cortical microarchitectural deterioration, increased bone turnover indices, and advanced cartilage degeneration, thus demonstrating the crucial role of Notch2 in skeletal and cartilage homeostasis, which is in line with the findings of previous mouse models.

Oral Surgery Procedures in a Patient with Hajdu-Cheney Syndrome Treated with Denosumab-A Rare Case Report

Background: Hajdu-Cheney syndrome (HCS) is a very rare autosomal-dominant congenital disease associated with mutations in the NOTCH2 gene. This disorder affects the connective tissue and is characterized by severe bone resorption. Hajdu-Cheney syndrome most frequently affects the head and feet bones (acroosteolysis). Case report: We present an extremely rare case of a 34-year-old male with Hajdu-Cheney syndrome. The patient was admitted to the Department of Oral Surgery, Medical University of Gdańsk, in order to perform the extraction of three teeth. These teeth were not eligible for conservative treatment and prosthetic reconstruction. The patient was treated with denosumab (angiogenesis and receptor activator of nuclear factor-κB RANK ligand inhibitor, RANKL). Discussion: Denosumab is a monoclonal antibody against RANKL. This drug works through a suppression of osteoclast activity. In cases of patients in which the pathway of the RANK/RANKL/osteoprotegerin is dysregulated, denosumab has been approved for the treatment off-label. In patients receiving denosumab, a delayed wound healing in the oral cavity and osteonecrosis may occur. Dental procedures involving the alveolar bone process (tooth extractions and bone alveoloplasty) may be a risk factor for medication-related osteonecrosis of the jaw (MRONJ). Spontaneous osteonecrosis is rarely observed. MRONJ consists of the destruction of exposed bone, with the exposure persisting for a minimum of 6–8 weeks. This is the first article about an HCS patient treated with denosumab who underwent invasive oral surgery procedures. This case report highlights the difficulties for professionals occurring during the oral surgery procedures in such patients.

Lost bones: differential diagnosis of acro-osteolysis seen by the pediatric rheumatologist

INTRODUCTION

Acro-osteolysis is a radiographic finding which refers to bone resorption of the distal phalanges. Acro-osteolysis is associated with various conditions and its presence should prompt the clinician to search for the underlying etiology. The aim of this review is to discuss disorders with which acro-osteolysis is associated and their distinguishing features, with a focus on the pediatric population.

METHODS

A targeted literature review was performed using the term "acro-osteolysis" in combination with other key terms. The primary search results were supplemented using reference citations. Articles published prior to the year 2000 were included if they described additional associations not encountered in the more recent literature.

RESULTS

Genetic disorders (particularly primary hypertrophic osteoarthropathy and skeletal dysplasias) and rheumatic diseases (particularly psoriatic arthritis and systemic sclerosis) are the most frequently encountered conditions associated with acro-osteolysis in children. Hyperparathyroidism, neuropathy, local trauma and thermal injury, and spinal dysraphism should also be included in the differential diagnosis.

CONCLUSION

Although acro-osteolysis is uncommon, its presence should prompt the clinician to consider a differential diagnosis based on clinical and radiographic features.

Clinical relevance of targeted exome sequencing in patients with rare syndromic short stature

BACKGROUND

Large-scale genomic analyses have provided insight into the genetic complexity of short stature (SS); however, only a portion of genetic causes have been identified. In this study, we identified disease-causing mutations in a cohort of Korean patients with suspected syndromic SS by targeted exome sequencing (TES).

METHODS

Thirty-four patients in South Korea with suspected syndromic disorders based on abnormal growth and dysmorphic facial features, developmental delay, or accompanying anomalies were enrolled in 2018-2020 and evaluated by TES.

RESULTS

For 17 of 34 patients with suspected syndromic SS, a genetic diagnosis was obtained by TES. The mean SDS values for height, IGF-1, and IGFBP-3 for these 17 patients were - 3.27 ± 1.25, - 0.42 ± 1.15, and 0.36 ± 1.31, respectively. Most patients displayed distinct facial features (16/17) and developmental delay or intellectual disability (12/17). In 17 patients, 19 genetic variants were identified, including 13 novel heterozygous variants, associated with 15 different genetic diseases, including many inherited rare skeletal disorders and connective tissue diseases (e.g., cleidocranial dysplasia, Hajdu-Cheney syndrome, Sheldon-Hall, acromesomelic dysplasia Maroteaux type, and microcephalic osteodysplastic primordial dwarfism type II). After re-classification by clinical reassessment, including family member testing and segregation studies, 42.1% of variants were pathogenic, 42.1% were likely pathogenic variant, and 15.7% were variants of uncertain significance. Ultra-rare diseases accounted for 12 out of 15 genetic diseases (80%).

CONCLUSIONS

A high positive result from genetic testing suggests that TES may be an effective diagnostic approach for patients with syndromic SS, with implications for genetic counseling. These results expand the mutation spectrum for rare genetic diseases related to SS in Korea.

To Be, or Notch to Be: Mediating Cell Fate from Embryogenesis to Lymphopoiesis

Notch signaling forms an evolutionarily conserved juxtacrine pathway crucial for cellular development. Initially identified in Drosophila wing morphogenesis, Notch signaling has since been demonstrated to play pivotal roles in governing mammalian cellular development in a large variety of cell types. Indeed, abolishing Notch constituents in mouse models result in embryonic lethality, demonstrating that Notch signaling is critical for development and differentiation. In this review, we focus on the crucial role of Notch signaling in governing embryogenesis and differentiation of multiple progenitor cell types. Using hematopoiesis as a diverse cellular model, we highlight the role of Notch in regulating the cell fate of common lymphoid progenitors. Additionally, the influence of Notch through microenvironment interplay with lymphoid cells and how dysregulation influences disease processes is explored. Furthermore, bi-directional and lateral Notch signaling between ligand expressing source cells and target cells are investigated, indicating potentially novel therapeutic options for treatment of Notch-mediated diseases. Finally, we discuss the role of cis-inhibition in regulating Notch signaling in mammalian development.

Hajdu-Cheney Syndrome: A Report on Successful Halting of Acro-osteolysis

CASE

The phenomenon of acro-osteolysis often intrigues clinicians and patients alike, as it causes bone resorption. One such condition is Hajdu-Cheney syndrome. We report our experience in identifying and halting the active bone resorption in a patient and his father with 2-year follow-up results.

CONCLUSION

Management included identification of the NOTCH2 mutation and treatment with antiresorptive measures. In addition, genetic counseling and antenatal counseling are recommended to explain the risk of inheritance.

Hajdu Cheney Syndrome due to NOTCH2 defect - First case report from Pakistan and review of literature

INTRODUCTION AND IMPORTANCE

Hajdu Cheney Syndrome (HCS) is a rare skeletal disease characterized by severe, progressive focal bone loss with osteoporosis, variable craniofacial, vertebral anomalies and distinctive facial features. It is inherited as an autosomal dominant disease although sporadic cases have been described in literature. Identifying these cases in clinical practice is important for proper diagnosis and management.

CASE PRESENTATION

We report a case of a 36-year-old male patient presented at metabolic bone disease clinic at the Aga Khan University Hospital with history of multiple fragility fractures and juvenile osteoporosis since childhood. DNA sequence analysis of the NOTCH2 coding sequence revealed a pathogenic variant in NOTCH 2, Exon 34, c.6426_6427insTT (p.Glu2143Leufs*5), consistent with a NOTCH2 related conditions including HCS.

CLINICAL DISCUSSION

The multitude of presentations associated with HCS are linked to the NOTCH2 gene, as Notch signaling is one of the core signaling pathways that control embryonic development. Hence, mutations in the Notch signaling pathway cause developmental phenotypes that affect various organs including the liver, skeleton, heart, eye, face, kidney, and vasculature.

CONCLUSION

To the best of our knowledge, nucleotide mutations of c.6933delT, c.6854delA, c.6787C.T, and c.6424-6427delTCTG were all determined to be novel, with c.6428T > C being the most common mutation found in literature. The c.6426_6427insTT mutation our patient was found to have via gene sequencing too appears to be a novel mutation, which has not previously been reported in literature.

Relevance of Notch Signaling for Bone Metabolism and Regeneration

Notch1-4 receptors and their signaling pathways are expressed in almost all organ systems and play a pivotal role in cell fate decision by coordinating cell proliferation, differentiation and apoptosis. Differential expression and activation of Notch signaling pathways has been observed in a variety of organs and tissues under physiological and pathological conditions. Bone tissue represents a dynamic system, which is constantly remodeled throughout life. In bone, Notch receptors have been shown to control remodeling and regeneration. Numerous functions have been assigned to Notch receptors and ligands, including osteoblast differentiation and matrix mineralization, osteoclast recruitment and cell fusion and osteoblast/osteoclast progenitor cell proliferation. The expression and function of Notch1-4 in the skeleton are distinct and closely depend on the temporal expression at different differentiation stages. This review addresses the current knowledge on Notch signaling in adult bone with emphasis on metabolism, bone regeneration and degenerative skeletal disorders, as well as congenital disorders associated with mutant Notch genes. Moreover, the crosstalk between Notch signaling and other important pathways involved in bone turnover, including Wnt/β-catenin, BMP and RANKL/OPG, are outlined.

The Skeleton of Lateral Meningocele Syndrome

Notch (Notch1 through 4) are transmembrane receptors that determine cell differentiation and function, and are activated following interactions with ligands of the Jagged and Delta-like families. Notch has been established as a signaling pathway that plays a critical role in the differentiation and function of cells of the osteoblast and osteoclast lineages as well as in skeletal development and bone remodeling. Pathogenic variants of Notch receptors and their ligands are associated with a variety of genetic disorders presenting with significant craniofacial and skeletal manifestations. Lateral Meningocele Syndrome (LMS) is a rare genetic disorder characterized by neurological manifestations, meningoceles, skeletal developmental abnormalities and bone loss. LMS is associated with NOTCH3 gain-of-function pathogenic variants. Experimental mouse models of LMS revealed that the bone loss is secondary to increased osteoclastogenesis due to enhanced expression of receptor activator of nuclear factor kappa B ligand by cells of the osteoblast lineage. There are no effective therapies for LMS. Antisense oligonucleotides targeting Notch3 and antibodies that prevent the activation of NOTCH3 are being tested in preclinical models of the disease. In conclusion, LMS is a serious genetic disorder associated with NOTCH3 pathogenic variants. Novel experimental models have offered insight on mechanisms responsible and ways to correct the disease.

Transcriptome Analysis Reveals High Similarities between Adult Human Cardiac Stem Cells and Neural Crest-Derived Stem Cells

For the identification of a stem cell population, the comparison of transcriptome data enables the simultaneous analysis of tens of thousands of molecular markers and thus enables the precise distinction of even closely related populations. Here, we utilized global gene expression profiling to compare two adult human stem cell populations, namely neural crest-derived inferior turbinate stem cells (ITSCs) of the nasal cavity and human cardiac stem cells (hCSCs) from the heart auricle. We detected high similarities between the transcriptomes of both stem cell populations, particularly including a range of neural crest-associated genes. However, global gene expression likewise reflected differences between the stem cell populations with regard to their niches of origin. In a broader analysis, we further identified clear similarities between ITSCs, hCSCs and other adherent stem cell populations compared to non-adherent hematopoietic progenitor cells. In summary, our observations reveal high similarities between adult human cardiac stem cells and neural crest-derived stem cells from the nasal cavity, which include a shared relation to the neural crest. The analyses provided here may help to understand underlying molecular regulators determining differences between adult human stem cell populations.

Obstructive hydrocephalus treated with endoscopic third ventriculostomy in a patient with Hajdu-Cheney syndrome: case report

Hajdu-Cheney syndrome (HCS) is a rare genetic disorder with autosomal dominant inheritance, although most cases result from de novo mutations. Progressive platybasia and basilar impression (BI) can potentiate obstructive hydrocephalus due to aqueductal stenosis. Limited literature exists on the surgical intervention for hydrocephalus in patients with this condition. The authors present (to their knowledge) the first case of obstructive hydrocephalus due to aqueductal stenosis from BI treated with an endoscopic third ventriculostomy in a patient with the complex anatomy of HCS.

Distinct severity of phenotype in Hajdu-Cheney syndrome: a case report and literature review

Background

Hajdu-Cheney syndrome (HCS) is a rare inherited skeletal disorder caused by pathogenic mutations in exon 34 of NOTCH2. Its highly variable phenotypes make early diagnosis challenging. In this paper, we report a case of early-onset HCS with severe phenotypic manifestations but delayed diagnosis.

Case presentation

The patient was born to non-consanguineous, healthy parents of Chinese origin. She presented facial anomalies, micrognathia and skull malformations at birth, and was found hearing impairment, congenital heart disease and developmental delay during her first year of life. Her first visit to our center was at 1 year of age due to cardiovascular repair surgery for patent ductus arteriosus (PDA) and ventricular septal defect (VSD). Skull X-ray showed wormian bones. She returned at 7 years old after she developed progressive skeletal anomalies with fractures. She presented with multiple wormian bones, acro-osteolysis, severe osteoporosis, bowed fibulae and a renal cyst. Positive genetic test of a de novo heterozygous frameshift mutation in exon 34 of NOTCH2 (c.6426dupT) supported the clinical diagnosis of HCS.

Conclusion

This is the second reported HCS case caused by the mutation c.6426dupT in NOTCH2, but presenting much earlier and severer clinical expression. Physicians should be aware of variable phenotypes so that early diagnosis and management may be achieved.

Diagnosis of monogenic chronic kidney diseases

PURPOSE OF REVIEW

The purpose of this review is to emphasize that single gene disorders are an important and sometimes unrecognized cause of progressive chronic kidney disease. We provide an overview of the benefits of making a genetic diagnosis, the currently available genetic testing methods and examples of diseases illustrating the impact of a genetic diagnosis.

RECENT FINDINGS

Although there are now a number of monogenic renal diseases, only a few, such as autosomal dominant polycystic kidney disease (ADPKD), are generally diagnosable without genetic testing. Complicating clinical diagnosis is that many diseases that classically have characteristic renal or extrarenal findings, often present with an incomplete or overlapping phenotype that requires additional testing to be uncovered. Advances in sequencing technology and bioinformatic processing now give us the ability to screen the entire human genome or exome or an organ-limited subset of genes quickly and inexpensively permitting the unbiased interrogation of hundreds of genes, thus removing the need for precision in clinical diagnosis prior to testing.

SUMMARY

We provide an overview of the principal phenotypes seen in chronic kidney disease with a focus on the cystic diseases and ciliopathies, the glomerular diseases, disorders of renal development and the tubulointerstitial diseases. In each of these phenotypes, we provide a listing of some of the important genes that have been identified to date, a brief discussion of the clinical diagnosis, the role of genetic testing and the differentiation of distinct genetic disorders from acquired and genetic phenocopies.

Neurosurgical Management of Lateral Meningocele Syndrome: A Clinical Update for the Pediatric Neurosurgeon

BACKGROUND

Lateral meningocele syndrome (LMS) is an exceedingly rare connective tissue disease with phenotypic anomalies similar to those seen in Marfan syndrome, Ehler-Danlos syndrome, and Loeys-Dietz syndrome. However, this syndrome is invariably associated with the presence of multiple lateral thoracolumbar spinal meningoceles: a distinct point of phenotypic divergence from other connective tissue disorders. The etiopathogenesis of this syndrome has recently been linked to truncating mutations within exon 33 of NOTCH3. Despite numerous reports, neurosurgical management of multiple spinal meningoceles remains poorly defined in the literature. We conducted a literature review to provide insight into the nosology, clinical significance, and neurosurgical management strategies of this distinct connective tissue disorder.

SUMMARY

Our literature search revealed 11 articles (16 cases) of LMS, which included 9 males and 7 females, belonging to 14 different families. Half of these cases underwent genetic screening: all of which were discovered to exhibit a truncating mutation within exon 33 of NOTCH3. All patients exhibited multiple lateral thoracolumbar spinal meningoceles with craniofacial dysmorphisms. Other clinical characteristics included pathologic changes in spine morphology, Chiari I malformation, syringomyelia, hydrocephalus, and tethered cord. Operative management of multiple spinal meningoceles in LMS is complicated by the presence of such coexisting structural neurologic pathologies, which may alter cerebrospinal fluid flow dynamics and, ultimately, impact operative intervention. Key Messages: LMS is an exceedingly rare connective tissue disorder with severe spinal dural involvement. Neurosurgical management of multiple spinal meningoceles is complex, which is further complicated by the presence of coexisting neuropathology, such as pathologic transformation of spine morphology and Chiari I malformation. Patients with a connective tissue disorder phenotype found to have multiple spinal meningoceles on imaging studies may benefit from evaluation by a medical geneticist and a pediatric neurosurgeon.

Notch Pathway and Inherited Diseases: Challenge and Promise

The evolutionary highly conserved Notch pathway governs many cellular core processes including cell fate decisions. Although it is characterized by a simple molecular design, Notch signaling, which first developed in metazoans, represents one of the most important pathways that govern embryonic development. Consequently, a broad variety of independent inherited diseases linked to defective Notch signaling has now been identified, including Alagille, Adams-Oliver, and Hajdu-Cheney syndromes, CADASIL (cerebral autosomal-dominant arteriopathy with subcortical infarcts and leukoencephalopathy), early-onset arteriopathy with cavitating leukodystrophy, lateral meningocele syndrome, and infantile myofibromatosis. In this review, we give a brief overview on molecular pathology and clinical findings in congenital diseases linked to the Notch pathway. Moreover, we discuss future developments in basic science and clinical practice that may emerge from recent progress in our understanding of the role of Notch in health and disease.

Notch Signaling in Kidney Development, Maintenance, and Disease

Kidney development involves formation of nephrons intricately aligned with the vasculature and connected to a branched network of collecting ducts. Notch signaling plays multiple roles during kidney development involving the formation of nephrons composed of diverse epithelial cell types arranged into tubular segments, all the while maintaining a nephron progenitor niche. Here, we review the roles of Notch signaling identified from rodent kidney development and injury studies, while discussing human kidney diseases associated with aberrant Notch signaling. We also review Notch signaling requirement in maintenance of mature kidney epithelial cell states and speculate that Notch activity regulation mediates certain renal physiologic adaptations.

The Hajdu Cheney mutation sensitizes mice to the osteolytic actions of tumor necrosis factor α

Hajdu Cheney syndrome (HCS) is characterized by craniofacial developmental abnormalities, acro-osteolysis, and osteoporosis and is associated with gain-of-NOTCH2 function mutations. A mouse model of HCS termed Notch2^tm1.1Ecan harboring a mutation in exon 34 of Notch2 replicating the one found in HCS was used to determine whether the HCS mutation sensitizes the skeleton to the osteolytic effects of tumor necrosis factor α (TNFα). TNFα injected over the calvarial vault caused a greater increase in osteoclast number, osteoclast surface, and eroded surface in Notch2^tm1.1Ecan mice compared with littermate WT controls. Accordingly, the effect of TNFα on osteoclastogenesis was greatly enhanced in cultures of bone marrow-derived macrophages (BMMs) from Notch2^tm1.1Ecan mice when compared with the activity of TNFα in control cultures. TNFα induced the expression of Notch2 and Notch2 mutant mRNA by ∼2-fold, possibly amplifying the NOTCH2-dependent induction of osteoclastogenesis. The effect of TNFα on osteoclastogenesis in Notch2^tm1.1Ecan mutants depended on NOTCH2 activation because it was reversed by anti-NOTCH2 negative regulatory region and anti-jagged 1 antibodies. The inactivation of Hes1 prevented the TNFα effect on osteoclastogenesis in the context of the Notch2^tm1.1Ecan mutation. In addition, the induction of Il1b, but not of Tnfa and Il6, mRNA by TNFα was greater in Notch2^tm1.1Ecan BMMs than in control cells, possibly contributing to the actions of TNFα and NOTCH2 on osteoclastogenesis. In conclusion, the HCS mutation enhances TNFα-induced osteoclastogenesis and the inflammatory bone-resorptive response possibly explaining the acro-osteolysis observed in affected individuals.

New PCNT candidate missense variant in a patient with oral and maxillofacial osteodysplasia: a case report

Background

Osteodysplasia of the oral and maxillofacial bone is generally accompanied by systemic bone abnormalities (such as short stature, joint contracture) or other systemic abnormalities (such as renal, dermatological, cardiovascular, optic, or hearing disorders). However, it does not always present this way. Recent reports have suggested that genome-wide sequencing is an effective method for identifying rare or new disorders. Here, we performed whole-exome sequencing (WES) in a patient with a unique form of acquired, local osteodysplasia of the oral and maxillofacial region.

Case presentation

A 46-year-old woman presented to our hospital with the complaint of gradually moving mandibular teeth (for 6 months), changing facial appearance, and acquired osteolysis of the oral and maxillofacial bones, showing mandibular hypoplasia without family history. Upon skeletal examination, there were no abnormal findings outside of the oral and maxillofacial area; the patient had a height of 157 cm and bone mineral density (according to dual energy x-ray absorptiometry) of 90%. Results of blood and urine tests, including evaluation of bone metabolism markers and neurological and cardiovascular examinations, were normal. We performed WES of genomic DNA extracted from the blood of this patient and her mother, who did not have the disease, as a negative control. We identified 83 new missense variants in the patient, not detected in her mother, including a candidate single nucleotide variant in exon 14 of PCNT (pericentrin). Critical homozygous or compound heterozygous variants in PCNT are a known cause of microcephalic osteodysplastic primordial dwarfism type II accompanied by mandibular hypoplasia, which is similar to the maxillofacial phenotype in this patient.

Conclusions

Protein simulations performed using Polymorphism Phenotyping v2 and Combined Annotation Dependent Depletion software indicated that this missense variant is likely to disrupt the PCNT protein structure. These results suggest that this is a new form of osteolysis related to this PCNT variant.

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.

Phenotypic presentations of Hajdu-Cheney syndrome according to age - 5 distinct clinical presentations

We present five Danish individuals with Hajdu-Cheney syndrome (HJCYS) (OMIM #102500), a rare multisystem skeletal disorder with distinctive facies, generalised osteoporosis and progressive focal bone destruction. In four cases positive genetic screening of exon 34 of NOTCH2 supported the clinical diagnosis; in one of these cases, mosaicism was demonstrated, which, to our knowledge, has not previously been reported. In one case no genetic testing was performed since the phenotype was definite, and the diagnosis in the mother was genetically confirmed. The age of the patients differs widely from ten to 57 years, allowing a natural history description of the phenotype associated with this ultra-rare condition. The evolution of the condition is most apparent in the incremental bone loss leading to osteoporosis and the acro-osteolysis, both of which contribute significantly to disease burden.

Profilin 1 Negatively Regulates Osteoclast Migration in Postnatal Skeletal Growth, Remodeling, and Homeostasis in Mice

Profilin 1 (Pfn1), a regulator of actin polymerization, controls cell movement in a context-dependent manner. Pfn1 supports the locomotion of most adherent cells by assisting actin-filament elongation, as has been shown in skeletal progenitor cells in our previous study. However, because Pfn1 has also been known to inhibit migration of certain cells, including T cells, by suppressing branched-end elongation of actin filaments, we hypothesized that its roles in osteoclasts may be different from that of osteoblasts. By investigating the osteoclasts in culture, we first verified that Pfn1-knockdown (KD) enhances bone resorption in preosteoclastic RAW264.7 cells, despite having a comparable number and size of osteoclasts. Pfn1-KD in bone marrow cells showed similar results. Mechanistically, Pfn1-KD osteoclasts appeared more mobile than in controls. In vivo, the osteoclast-specific conditional Pfn1-deficient mice (Pfn1-cKO) by CathepsinK-Cre driver demonstrated postnatal skeletal phenotype, including dwarfism, craniofacial deformities, and long-bone metaphyseal osteolytic expansion, by 8 weeks of age. Metaphyseal and diaphyseal femurs were drastically expanded with suppressed trabecular bone mass as indicated by μCT analysis. Histologically, TRAP-positive osteoclasts were increased at endosteal metaphysis to diaphysis of Pfn1-cKO mice. The enhanced movement of Pfn1-cKO osteoclasts in culture was associated with a slight increase in cell size and podosome belt length, as well as an increase in bone-resorbing activity. Our study, for the first time, demonstrated that Pfn1 has critical roles in inhibiting osteoclast motility and bone resorption, thereby contributing to essential roles in postnatal skeletal homeostasis. Our study also provides novel insight into understanding skeletal deformities in human disorders.

Congenital Glaucoma: a Novel Ocular Manifestation of Hajdu-Cheney Syndrome

Hajdu-Cheney Syndrome (HSC) is a rare multisystem disease in which the phenotype involves acro-osteolysis, severe osteoporosis, short stature, wormian bones, facial dysmorphism, central neurological abnormalities, cardiovascular defects, and polycystic kidneys. We describe an infant with severe manifestations of HCS in whom congenital glaucoma was a significant early feature, which has not been reported to date. HCS cases reported to date have involved truncating mutations in exon 34 of NOTCH2 upstream the PEST domain that lead to the development of a truncated and stable NOTCH2 protein which upregluates notch signaling. We describe a hitherto undescribed missense mutation that is predicted to be pathogenic, with functional characterization remaining to be performed. Serpentine fibula-polycystic kidney syndrome (SFPKS) is allelic to HCS and commonly associated with missense NOTCH2 mutations. Our patient provides new ophthalmological manifestations of HCS and provides insight into the potential role of notch signaling in the anterior chamber development.

Dental implications in Hajdu-Cheney syndrome: A novel case report and review of the literature

OBJECTIVE

To identify the molecular genetic etiology of an individual with a dysmorphic face, unusual teeth mobility, and root resorption.

SUBJECTS AND METHODS

DNA samples were collected from a trio of family members, and whole-exome sequencing was performed.

RESULTS

Mutational analysis revealed a de novo mutation (c.6787C>T) in the last exon of the NOTCH2 gene. This mutation would introduce a premature stop codon [p.(Gln2263*)] and generate a truncated protein without C-terminus, escaping from the nonsense-mediated decay system. Sanger sequencing confirmed that this mutation was generated spontaneously.

CONCLUSIONS

In this study, we identified a novel nonsense mutation in the last exon of the NOTCH2 gene causing Hajdu-Cheney syndrome. We described the genotype and phenotype correlation and the related dental complications. These results will advance the understanding of the NOTCH2 signaling in periodontitis and root resorption.

Neurocristopathies: New insights 150 years after the neural crest discovery

The neural crest (NC) is a transient, multipotent and migratory cell population that generates an astonishingly diverse array of cell types during vertebrate development. These cells, which originate from the ectoderm in a region lateral to the neural plate in the neural fold, give rise to neurons, glia, melanocytes, chondrocytes, smooth muscle cells, odontoblasts and neuroendocrine cells, among others. Neurocristopathies (NCP) are a class of pathologies occurring in vertebrates, especially in humans that result from the abnormal specification, migration, differentiation or death of neural crest cells during embryonic development. Various pigment, skin, thyroid and hearing disorders, craniofacial and heart abnormalities, malfunctions of the digestive tract and tumors can also be considered as neurocristopathies. In this review we revisit the current classification and propose a new way to classify NCP based on the embryonic origin of the affected tissues, on recent findings regarding the molecular mechanisms that drive NC formation, and on the increased complexity of current molecular embryology techniques.

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.