Geometric growth of the normal human craniocervical junction from 0 to 18 years old

The craniocervical junction (CCJ) forms the bridge between the skull and the spine, a highly mobile group of joints that allows the mobility of the head in every direction. The CCJ plays a major role in protecting the inferior brainstem (bulb) and spinal cord, therefore also requiring some stability. Children are subjected to multiple constitutive or acquired diseases involving the CCJ: primary bone diseases such as in FGFR-related craniosynostoses or acquired conditions such as congenital torticollis, cervical spine luxation, and neurological disorders. To design efficient treatment plans, it is crucial to understand the relationship between abnormalities of the craniofacial region and abnormalities of the CCJ. This can be approached by the study of control and abnormal growth patterns. Here we report a model of normal skull base growth by compiling a collection of geometric models in control children. Focused analyses highlighted specific developmental patterns for each CCJ bone, emphasizing rapid growth during infancy, followed by varying rates of growth and maturation during childhood and adolescence until reaching stability by 18 years of age. The focus was on the closure patterns of synchondroses and sutures in the occipital bone, revealing distinct closure trajectories for the anterior intra-occipital synchondroses and the occipitomastoid suture. The findings, although based on a limited dataset, showcased specific age-related changes in width and closure percentages, providing valuable insights into growth dynamics within the first 2 years of life. Integration analyses revealed intricate relationships between skull and neck structures, emphasizing coordinated growth at different stages. Specific bone covariation patterns, as found between the first and second cervical vertebrae (C1 and C2), indicated synchronized morphological changes. Our results provide initial data for designing inclusive CCJ geometric models to predict normal and abnormal growth dynamics.

An FGFR2 mutation as the potential cause of a new phenotype including early-onset osteoporosis and bone fractures: a case report

Osteoporosis is a systemic, multifactorial disorder of bone mineralization. Many factors contributing to the development of osteoporosis have been identified so far, including gender, age, nutrition, lifestyle, exercise, drug use, as well as a range of comorbidities. In addition to environmental and lifestyle factors, molecular genetic factors account for 50-85% of osteoporosis cases. For example, the vitamin D receptor (VDR), collagen type I (COL1), estrogen receptor (ER), apolypoprotein Е (ApoE), bone morphogenetic protein (BMP), and Low-density lipoprotein receptor-related protein 5 (LRP5) are all involved in the pathogenesis of osteoporosis. Among the candidate genes, the pathogenic variants in which are involved in the pathogenesis of osteoporosis is FGFR2. Additionally, FGFs/FGFRs-dependent signaling has been shown to regulate skeletal development and has been linked to a plethora of heritable disorders of the musculoskeletal system. In this study we present the clinical, biochemical and radiological findings, as well as results of molecular genetic testing of a 13-year-old male proband with heritable osteoporosis, arthralgia and multiple fractures and a family history of abnormal bone mineralization and fractures. Whole exome sequencing found a heterozygous previously undescribed variant in the FGFR2 gene (NM_000141.5) (GRCh37.p13 ENSG00000066468.16: g.123298133dup; ENST00000358487.5:c.722dup; ENSP00000351276.5:p.Asn241LysfsTer43). The same variant was found in two affected relatives. These data lead us to believe that the variant in FGFR2 found in our proband and his relatives could be related to their phenotype. Therefore, modern methods of molecular genetic testing can allow us to differentiate between osteogenesis imperfecta and other bone mineralization disorders.

Infigratinib, a selective FGFR1-3 tyrosine kinase inhibitor, alters dentoalveolar development at high doses

BACKGROUND

Fibroblast growth factor receptor-3 (FGFR3) gain-of-function mutations are linked to achondroplasia. Infigratinib, a FGFR1-3 tyrosine kinase inhibitor, improves skeletal growth in an achondroplasia mouse model. FGFs and their receptors have critical roles in developing teeth, yet effects of infigratinib on tooth development have not been assessed. Dentoalveolar and craniofacial phenotype of Wistar rats dosed with low (0.1 mg/kg) and high (1.0 mg/kg) dose infigratinib were evaluated using micro-computed tomography, histology, and immunohistochemistry.

RESULTS

Mandibular third molars were reduced in size and exhibited aberrant crown and root morphology in 100% of female rats and 80% of male rats at high doses. FGFR3 and FGF18 immunolocalization and extracellular matrix protein expression were unaffected, but cathepsin K (CTSK) was altered by infigratinib. Cranial vault bones exhibited alterations in dimension, volume, and density that were more pronounced in females. In both sexes, interfrontal sutures were significantly more patent with high dose vs vehicle.

CONCLUSIONS

High dose infigratinib administered to rats during early stages affects dental and craniofacial development. Changes in CTSK from infigratinib in female rats suggest FGFR roles in bone homeostasis. While dental and craniofacial disruptions are not expected at therapeutic doses, our findings confirm the importance of dental monitoring in clinical studies.

Unravelling the pathogenesis of foramen magnum stenosis in patients with severe achondroplasia: a CT-based comparison with age-matched controls and FGFR3 craniosynostosis syndromes

OBJECTIVE

Foramen magnum(FM) stenosis can be responsible for acute and chronic damage to the cervicomedullary junction in children with achondroplasia. The bony anatomy and patterns of suture fusion of the FM in this context are incompletely understood, yet becoming increasingly important in the light of novel medical therapies for achondroplasia. The objective of this study was to describe and quantify bony anatomy and fusion patterns of FM stenosis in patients with achondroplasia using CT scans, comparing them to age-matched controls and other FGFR3 craniosynostosis patients.

METHODS

Patients with achondroplasia and severe FM stenosis, classified as achondroplasia foramen magnum score(AFMS) grades 3 and 4, were identified from a departmental operative database. All had pre-operative CT scans of the craniocervical junction. Measurements obtained comprised sagittal diameter (SD), transverse diameter (TD), foramen magnum area, and opisthion thickness. Anterior and posterior interoccipital synchondroses (AIOS and PIOS) were graded by the extent of fusion. These measurements were then compared with CT scans from 3 age-matched groups: the normal control group, children with Muenke syndrome, and children with Crouzon syndrome with acanthosis nigricans (CSAN).

RESULTS

CT scans were reviewed in 23 cases of patients with achondroplasia, 23 normal controls, 20 Muenke, and 15 CSAN. Children with achondroplasia had significantly smaller sagittal diameter (mean 16.2 ± 2.4 mm) compared to other groups (control 31.7 ± 2.4 mm, p < 0.0001; Muenke 31.7 ± 3.5 mm, p < 0.0001; and CSAN 23.1 ± 3.4 mm, p < 0.0001) and transverse diameters (mean 14.3 ± 1.8 mm) compared with other groups (control 26.5 ± 3.2 mm, p < 0.0001; Muenke 24.1 ± 2.6 mm, p < 0.0001; CSAN 19.1 ± 2.6 mm, p < 0.0001). This translated into a surface area which was 3.4 times smaller in the achondroplasia group compared with the control group. The median grade of the AIOS fusion achondroplasia group was 3.0 (IQR 3.0-5.0), which was significantly higher compared with the control group (1.0, IQR 1.0-1.0, p < 0.0001), Muenke group (1.0, IQR 1.0-1.0, p < 0.0001), and CSAN (2.0, IQR 1.0-2.0, p < 0.0002). Median PIOS fusion grade was also highest in the achondroplasia group (5.0, IQR 4.0-5.0) compared with control (1.0, IQR 1.0-1.0, p < 0.0001), Muenke (2.5, IQR 1.3-3.0, p < 0.0001), and CSAN (4.0, IQR 4.0-4.0, p = 0.2). Distinct bony opisthion spurs projecting into the foramen magnum were seen in achondroplasia patients but not others, resulting in characteristic crescent and cloverleaf shapes.

CONCLUSION

Patients with AFMS stages 3 and 4 have significantly reduced FM diameters, with surface area 3.4 times smaller than age-matched controls. This is associated with premature fusion of the AIOS and PIOS in comparison with controls and other FGFR3-related conditions. The presence of thickened opisthion bony spurs contributes to stenosis in achondroplasia. Understanding and quantifying bony changes at the FM of patients with achondroplasia will be important in the future quantitative evaluation of emerging medical therapies.

Overexpression of fibroblast growth factor receptor 2 in bone marrow mesenchymal stem cells enhances osteogenesis and promotes critical cranial bone defect regeneration

Background: Reconstruction of cranial bone defects is one of the most challenging problems in reconstructive surgery, and several biological tissue engineering methods have been used to promote bone repair, such as genetic engineering of bone marrow mesenchymal stem cells (BMSCs). Fibroblast growth factor receptor 2 (Fgfr2) is an important regulator of bone construction and can be used as a potential gene editing site. However, its role in the osteogenesis process of BMSCs remains unclear. This article clarifies the function of Fgfr2 in BMSCs and explores the role of Fgfr2-overexpressed BMSCs carried by light-induced porous hydrogel (GelMA) in the repair of cranial bone defects. Methods: Lenti-virus was used to overexpress Fgfr2 in BMSCs, and cell counting kit-8, transwell, and flow cytometry assays were conducted to investigate the proliferation, migration, and characteristics. After 0, 3, 7, and 10 days of osteogenic or chondrogenic induction, the changes in osteogenic and chondrogenic ability were detected by real-time PCR, western blot, alkaline phosphatase staining, alizarin Red staining, and alcian blue staining. To investigate the viability of BMSCs carried by GelMA, calcein and propyl iodide staining were carried out as well. Finally, a critical cranial bone defect model was established in 6-week-old male mice and micro-computerized tomography, masson staining, and immunohistochemistry of OCN were conducted to test the bone regeneration properties of implanting Fgfr2-overexpressed BMSCs with GelMA in cranial bone defects over 6 weeks. Results: Overexpression of Fgfr2 in BMSCs significantly promoted cell proliferation and migration and increased the percentage of CD200+CD105+ cells. After osteogenic and chondrogenic induction, Fgfr2 overexpression enhanced both osteogenic and chondrogenic ability. Furthermore, in cranial bone defect regeneration, BMSCs carried by light-induced GelMA showed favorable biocompatibility, and Fgfr2-overexpressed BMSCs induced superior cranial bone regeneration compared to a normal BMSCs group and an untreated blank group. Conclusion: In vitro, Fgfr2 enhanced the proliferation, migration, and stemness of BMSCs and promoted osteogenesis and chondrogenesis after parallel induction. In vivo, BMSCs with Fgfr2 overexpression carried by GelMA showed favorable performance in treating critical cranial bone defects. This study clarifies the multiple functions of Fgfr2 in BMSCs and provides a new method for future tissue engineering.

Skeletal Dysplasia Families: A Stepwise Approach to Diagnosis

Skeletal dysplasias are a heterogeneous collection of genetic disorders characterized by bone and cartilage abnormalities, and they encompass over 400 disorders. These disorders are rare individually, but collectively they are common (approximate incidence of one in 5000 births). Radiologists occasionally encounter skeletal dysplasias in daily practice. In the 1980s, Professor Juergen Spranger proposed a concept suitable for the diagnosis of skeletal dysplasias termed bone dysplasia families. He stated that (a) different bone dysplasias that share a similar skeletal pattern can be grouped into a "family," (b) the final diagnosis is feasible through the provisional recognition of a pattern followed by a more careful analysis, and (c) families of bone dysplasias may be the result of similar pathogenetic mechanisms. The prototypes of bone dysplasia families include dysostosis multiplex family, achondroplasia family, spondyloepiphyseal dysplasia congenita family, and Larsen syndrome-otopalatodigital syndrome family. Since Spranger's proposal, the concept of bone dysplasia families, along with advancing genetic techniques, has been validated and further expanded. Today, this molecularly proven concept enables a simple stepwise approach to be applied to the radiologic diagnosis of skeletal dysplasias. The first step is the categorization of a given case into a family based on pattern recognition, and the second step is more meticulous observation, such as identification of different severities of the same pattern or subtle but distinctive findings. Since major skeletal dysplasias are limited in number, radiologists can be familiar with the representative patterns of these disorders. The authors describe a stepwise radiologic approach to diagnosing major skeletal dysplasia families and review the clinical and genetic features of these disorders. Published under a CC BY 4.0 license. Quiz questions for this article are available through the Online Learning Center. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

Clinical Manifestations and Outcomes of 20 Korean Hypochondroplasia Patients with the FGFR3 N540K variant

BACKGROUND

Hypochondroplasia is a skeletal dysplasia caused by activating pathologic variants of FGFR3. The N540K variant accounts for 60-70% of reported cases and is associated with severe manifestations. Here, we analyze the clinical manifestations and outcomes of Korean patients with hypochondroplasia harboring the FGFR3 N540K variant.

METHODS

Medical records of 20 unrelated patients with genetically confirmed N540K-related hypochondroplasia were retrospectively reviewed. All individuals were diagnosed with hypochondroplasia by Sanger sequencing for FGFR3, or target-panel sequencing for skeletal dysplasia. The effectiveness of growth hormone therapy was analyzed in 16 patients treated with growth hormones.

RESULTS

Among 20 patients (7 men, 13 women), the mean age at first visit was 3.5±1.0 years, and the mean follow-up duration was 6.8±0.6 years. The patients presented with a short stature and/or short limbs. Genu varum, macrocephaly, and developmental delay were observed in 11 (55.0%), 9 (45.0%), and 5 (25.0%) patients, respectively. Of the 12 patients who underwent neuroimaging, five (41.7%) showed abnormal findings (one required operation for obstructive hydrocephalus). Among 16 growth-hormone-treated patients (two were growth-hormone deficient), the increase in height standard deviation scores was significant after a mean 5.4±0.7 years of treatment (+0.6 and+1.8 using growth references for healthy controls and achondroplasia children, respectively). Four patients underwent surgical limb lengthening at a mean age of 8.8±3.3 years.

CONCLUSIONS

Neurodevelopmental abnormalities are frequently observed in patients with N540K-related hypochondroplasia. Close monitoring of skeletal manifestations and neurodevelopmental status is necessary for hypochondroplasia.

Identification of a novel mutation in FGFR1 gene in mother and daughter with Kallmann syndrome

OBJECTIVES

Congenital hypogonadotropic hypogonadism combined with anosmia or hyposmia is considered Kallmann syndrome (KS). It is often accompanied by bone defects.

CASE PRESENTATION

Here, we report a girl and her mother with KS caused by a novel mutation in the fibroblast growth factor receptor 1 gene (FGFR1). Interestingly, the daughter presented syndactyly and oligodactyly of the feet.

CONCLUSIONS

The presence of bone malformations in a KS patient should direct the geneticist towards a search for specific mutations in FGFR1. Our finding contributes to enrich the spectrum of FGFR1 mutations in patients with KS.

Clinical management and emerging therapies of FGFR3-related skeletal dysplasia in childhood

Skeletal dysplasia is a diverse group of disorders that affect bone development and morphology. Currently, approximately 461 different genetic skeletal disorders have been identified, with over 430 causative genes. Among these, fibroblast growth factor receptor 3 (FGFR3)-related skeletal dysplasia is a relatively common subgroup of skeletal dysplasia. Pediatric endocrinologists may encounter a suspected case of skeletal dysplasia in their practice, especially when evaluating children with short stature. Early and accurate diagnosis of FGFR3-related skeletal dysplasia is essential for timely management of complications and genetic counseling. This review summarizes 5 representative and distinct entities of skeletal dysplasia caused by pathogenic variants in FGFR3 and discusses emerging therapies for FGFR3-related skeletal dysplasias.

Severe presentation of non-ossifying fibroma of the femur in osteoglophonic dysplasia

Osteoglophonic dwarfism, also known as osteoglophonic dysplasia (OD), is an uncommon skeletal dysplasia with an autosomal dominant mode of inheritance, which equally affects boys and girls. OD is saliently featured by craniosynostosis, dysmorphic facial features, impacted mandibular teeth, rhizomelic limb shortening and non-ossifying fibromas habitually at the metaphyseal regions, which usually disappear after skeletal maturity. The long bones in OD are portrayed by this distinguishable 'hollowed-out' appearance with metaphyseal cystic defects that have a natural history of spontaneous resolution. We report a case of a rare and unusual presentation of OD in a 23-year-old woman whom has been diagnosed with OD during her early childhood. She presented with a progressively enlarging right thigh swelling associated with pain for the past 1 year. Her right femur plain radiograph revealed diffuse lysis of the whole femur with cortical thinning. MRI revealed multiple bilateral femur benign cystic lesion synonymous with a severe spectrum of OD. She was started on a trial of oral bisphosphonates, which led to a significant improvement in pain.

Pictorial review: imaging of the spinal manifestations of achondroplasia

Achondroplasia is the commonest hereditary skeletal dysplasia exhibiting dwarfism with characteristic rhizomelic (proximal) shortening of the limbs. It is predominantly linked with an autosomal dominant inheritance, but sporadic mutations can occur which are associated with advanced maternal age. Approximately 1 in every 25 000-30 000 live births are affected, and the overall life expectancy is marginally reduced by ~10 years. Mutations in the fibroblast growth factor receptor causes a decrease in endochondral ossification, which results in stunted growth of cartilaginous bones. A resultant narrowed foramen magnum and a short clivus are seen which predisposes to craniocervical spinal canal stenosis. Apnoeic events arising from the compression of the vertebral arteries at the level of the craniocervical junction lead to fatality in the young, with a death rate as high as 7.5%. Decrease in the caudal inter-pedicular distance is characteristic and a contributory factor for cervical, thoracic and lumbar spinal canal stenosis, most pronounced in the lumbar spine with patients often requiring surgical intervention to ease symptoms. Thoracolumbar kyphoscoliosis and sacral manifestations such as small sacro-sciatic notches and a horizontal pelvis are seen. The aim of this pictorial review is to demonstrate the imaging findings of the spinal and pelvic manifestations of achondroplasia.

Craniosynostosis: Neonatal Perspectives

Craniosynostosis is the premature fusion of 1 or more sutures that normally separate the bony plates of an infant's skull and occurs in about 1 in 2,000 to 2,500 live births. Primary or congenital craniosynostoses represent the majority of cases and consist of single-suture and multisuture synostoses. Multisuture synostoses are typically associated with distinct craniofacial syndromes, including Muenke syndrome, Apert syndrome, Crouzon syndrome, and Pfeiffer syndrome, and are thus categorized under syndromic craniosynostoses. Secondary causes of craniosynostoses include metabolic or hematologic disorders that affect bone metabolism and typically present much later than primary synostoses. The severity of the deformity and the presence of increased intracranial pressure dictate the need for early surgical intervention, prompting the importance of early recognition and timely referral. Infants with craniosynostosis are also at increased risk for neurodevelopmental impairment and thus require close follow-up and monitoring. The early recognition and referral of craniosynostosis is imperative for the optimization of management and minimization of potential neurologic impairments that may develop.

Revisiting Skeletal Dysplasias in the Newborn

With over 400 reported disorders, the skeletal dysplasias represent a myriad of molecularly-based skeletal abnormalities. Arising from errors in skeletal development, the clinical spectrum of disease evolves through an affected individual's life. The naming and grouping of these disorders are ever-changing, but the fundamentals of diagnosis remain the same and are accomplished through a combination of prenatal ultrasonography and postnatal physical examination, radiography, and genetic analysis. Although some disorders are lethal in the perinatal and neonatal periods, other disorders allow survival into infancy, childhood, and even adulthood with relatively normal lives. The foundation of management for an affected individual is multidisciplinary care. Medical advances have offered new insights into reducing common morbidities through pharmacologic means. This review summarizes the normal skeletal development and discusses the 3 most common skeletal dysplasias that can affect the newborn.

Chiari 1 malformation and exome sequencing in 51 trios: the emerging role of rare missense variants in chromatin-remodeling genes

Type 1 Chiari malformation (C1M) is characterized by cerebellar tonsillar herniation of 3–5 mm or more, the frequency of which is presumably much higher than one in 1000 births, as previously believed. Its etiology remains undefined, although a genetic basis is strongly supported by C1M presence in numerous genetic syndromes associated with different genes. Whole-exome sequencing (WES) in 51 between isolated and syndromic pediatric cases and their relatives was performed after confirmation of the defect by brain magnetic resonance image (MRI). Moreover, in all the cases showing an inherited candidate variant, brain MRI was performed in both parents and not only in the carrier one to investigate whether the defect segregated with the variant. More than half of the variants were Missense and belonged to the same chromatin-remodeling genes whose protein truncation variants are associated with severe neurodevelopmental syndromes. In the remaining cases, variants have been detected in genes with a role in cranial bone sutures, microcephaly, neural tube defects, and RASopathy. This study shows that the frequency of C1M is widely underestimated, in fact many of the variants, in particular those in the chromatin-remodeling genes, were inherited from a parent with C1M, either asymptomatic or with mild symptoms. In addition, C1M is a Mendelian trait, in most cases inherited as dominant. Finally, we demonstrate that modifications of the genes that regulate chromatin architecture can cause localized anatomical alterations, with symptoms of varying degrees.

Evaluation of exposure dose in fetal computed tomography using organ-effective modulation

Organ-effective modulation (OEM) is a computed tomography scanning technique that reduces the exposure dose to organs at risk. Ultrasonography is commonly used for prenatal imaging, but its reliability is reported to be limited. Radiography and computed tomography (CT) are reliable but pose risk of radiation exposure to the pregnant woman and her fetus. Although there are many reports on the exposure dose associated with fetal CT scans, no reports exist on OEM use in fetal CT scans. We measured the basic characteristics of organ-effective modulation (X-ray output modulation angle, maximum X-ray output modulation rate, total X-ray output modulation rate, and noise modulation) and used them in a Monte Carlo simulation to evaluate the effect of this technique on fetal CT scans in terms of image quality and exposure dose to the pregnant woman and fetus. Using ImPACT MC software, Monte Carlo simulations of OEMON and OEMOFF were run on 8 cases involving fetal CT scans. We confirmed that the organ-effective modulation X-ray output modulation angle was 160°; the X-ray output modulation rate increased with increasing tube current; and no modulation occurred at tube currents of 80 mA or below. Our findings suggest that OEM has only a minimal effect in reducing organ exposure in pregnant women; therefore, it should be used on the anterior side (OEMON,front) to reduce the exposure dose to the fetus.

HSPB7 regulates osteogenic differentiation of human adipose derived stem cells via ERK signaling pathway

Background

Heat shock protein B7 (HSPB7), which belongs to small heat shock protein family, has been reported to be involved in diverse biological processes and diseases. However, whether HSPB7 regulates osteogenic differentiation of human adipose derived stem cells (hASCs) remains unexplored.

Methods

The expression level of HSPB7 during the osteogenesis of hASCs was examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and Western blot analysis. Lentivirus transfection was used to knock down or overexpress HSPB7, which enabled us to investigate the effect of HSPB7 on osteogenic differentiation of hASCs. U0126 and extracellular signal-regulated protein kinase 1/2 (ERK1/2) siRNA were used to identify the mechanism of the HSPB7/ERK1/2 axis in regulating osteogenic differentiation of hASCs. Moreover, ectopic bone formation in nude mice and osteoporosis mice model was used to investigate the effect of HSPB7 on osteogenesis in vivo.

Results

In this study, we found the expression of HSPB7 was significantly downregulated during the osteogenic differentiation of hASCs. HSPB7 knockdown remarkably promoted osteogenic differentiation of hASCs, while HSPB7 overexpression suppressed osteogenic differentiation of hASCs both in vitro and in vivo. Moreover, we discovered that the enhancing effect of HSPB7 knockdown on osteogenic differentiation was related to the activation of extracellular signal-regulated protein kinase (ERK) signaling pathway. Inhibition of ERK signaling pathway with U0126 or silencing ERK1/2 effectively blocked the stimulation of osteogenic differentiation induced by HSPB7 knockdown. Additionally, we found that HSPB7 expression was markedly increased in mouse bone marrow mesenchymal stem cells (mBMSCs) from the osteoporotic mice which suggested that HSPB7 might be utilized as a potential target in the development of effective therapeutic strategies to treat osteoporosis and other bone diseases.

Conclusion

Taken together, these findings uncover a previously unrecognized function of HSPB7 in regulating osteogenic differentiation of hASCs, partly via the ERK signaling pathway.

Earlier detection of hypochondroplasia: A large single-center UK case series and systematic review

Hypochondroplasia (HCH) is a rare autosomal dominant skeletal dysplasia condition caused by FGFR3 mutations leading to disproportionate short stature. Classically HCH presents in toddlers or school-age children, as limb-to-trunk disproportion and is often mild and easily overlooked during infancy. We report experiences from a single-center UK HCH-cohort of 31 patients, the rate of antenatal HCH detection in our cohort (13/31, 41.9%) and describe relevant case-data for this subset of 13 patients. Inclusion criteria were patients with confirmed molecular HCH diagnosis (by age 3 years) and presenting with short long-bones or large head size on antenatal ultrasound scan. We then conducted a systematic literature review using PUBMED and MEDLINE, analyzing patients with HCH and related antenatal findings. Antenatally suspected (with subsequent molecular confirmation) HCH has been reported 15 times in the literature (2004-2019). Key markers (consistent in both groups) included reduced; femur length, humeral length and increased; biparietal diameter and head circumference. HCH is increasingly detected both antenatally and in infancy, contrary to previous descriptions. This is likely due to greater HCH awareness, improved imaging, and easier molecular testing. Thus, one should consider HCH outside the classical presenting period. Studying the natural history of younger patients with HCH is important with the advent of several targeted FGFR3 therapies currently in trials for Achondroplasia, that may soon be trialed in HCH.

Severe Cloverleaf Skull Deformity in c.1061C>G (p.Ser354Cys) Mutated Fibroblast Growth Factor Receptor 2 Gene in Crouzon Syndrome

ABSTRACT

Cloverleaf skull deformity (CSD), or Kleeblattschädel, is a condition with severe and unpatterned multisuture craniosynostosis, resulting in a trilobar-shaped skull. This deformity mainly comprises a cranio-orbito-facial malformation that leads to a spectrum of multidisciplinary issues. Several syndromes are associated with CSD, such as Crouzon syndrome (CS). Here, we report the case of an infant with CS and the pathogenic c.1061C>G (p.Ser354Cys) variant of the fibroblast growth factor receptor 2 (FGFR2) gene. The child presented with the severe form of CSD despite having a normal, mid-trimester, sonographic scan.

Mutational landscape and genetic signatures of cell-free DNA in tumour-induced osteomalacia

Tumour‐induced osteomalacia (TIO) is a very rare paraneoplastic syndrome with bone pain, fractures and muscle weakness, which is mostly caused by phosphaturic mesenchymal tumours (PMTs). Cell‐free DNA (cfDNA) has been regarded as a non‐invasive liquid biopsy for many malignant tumours. However, it has not been studied in benign tumours, which prompted us to adopt the targeted next‐generation sequencing approach to compare cfDNAs of 4 TIO patients, four patients with bone metastasis (BM) and 10 healthy controls. The mutational landscapes of cfDNA in TIO and BM groups were similar in the spectrum of allele frequencies and mutation types. Markedly, deleterious missense mutations in FGFR1 and loss‐of‐function mutations in MED12 were found in 3/4 TIO patients but none of BM patients. The gene ontology analysis strongly supported that these mutated genes found in TIOs would play a potential role in PMTs' process. The genetic signatures and corresponding change in expression of FGFR1 and FGF23 were further validated in PMT tissues from a test cohort of another three TIO patients. In summary, we reported the first study of the mutational landscape and genetic signatures of cfDNA in TIO/PMTs.

The primary role of radiological imaging in the diagnosis of rare musculoskeletal diseases. Emphasis on ultrasound

Objective: In July 2017 a multidisciplinary clinical Center specialized in rare diseases was activated. A rare disease can involve the musculoskeletal system. A multimodality musculoskeletal imaging approach allows for a rapid diagnosis. The purpose of this study was to assess when musculoskeletal radiology, ultrasound in particular, plays a primary role in the diagnostic path of a rare disease. Methods and materials: The Center included a list of 621 main rare diseases. Pathologies in which radiology has a primary diagnostic role were extracted from the list. From September 2017 to January 2018 all conditions involving the musculoskeletal system, including the peripheral nervous system, were systematically evaluated by one radiologist. The second radiologist, an official consultant of the Center, verified the list for consistency. Descriptive analysis was performed. Results: A total of 101/621 (16%) rare diseases can be diagnosed for the first time in the diagnostic path of the patient with medical imaging. A total of 36/101 (36%) rare diseases involve the musculoskeletal system. A total of 14/36 (39%) are pediatric diseases, 10/36 (28%) are adult age diseases, while 12/36 (33%) diseases affect all ages. A total of 23/36 (64%) of the selected rare diseases could be diagnosed with MRI, 19/36 (53%) with CT, 23/36 (64%) with X-ray, 9/36 (25%) with an US, and 1/36 (3%) with PET. Conclusions: Musculoskeletal imaging could be important for a non-invasive diagnosis in up to 36/101 (36%) rare diseases, as well as for outcome prediction, especially in pediatrics. Musculoskeletal imaging plays a crucial role in the diagnosis of rare diseases and could strongly influence the clinical pathway. Ultrasound is crucial in up to 25% of patients with rare diseases affecting the musculoskeletal system.

A framework for the radiologic diagnosis of skeletal dysplasias and syndromes as revealed by molecular genetics

This article simplifies the radiologic diagnosis of skeletal dysplasia by first presenting an ordered approach for analysis of standard radiographs done for skeletal dysplasias. With that foundation, a more detailed discussion of three separate families of skeletal disorders follows. Similarities among dysplasia group members are discussed to provide a certain connectedness among dysplasias. The paper also elucidates the scientific basis behind the radiographic findings so that previously purely descriptive terms have the weight of understanding behind them.

High Prevalence of Growth Plate Gene Variants in Children With Familial Short Stature Treated With GH

CONTEXT

Familial short stature (FSS) is a term describing a growth disorder that is vertically transmitted. Milder forms may result from the combined effect of multiple genes; more severe short stature is suggestive of a monogenic condition. The etiology of most FSS cases has not been thoroughly elucidated to date.

OBJECTIVES

To identify the genetic etiology of severe FSS in children treated with GH because of the diagnosis of small for gestational age or GH deficiency (SGA/GHD).

DESIGN, SETTINGS, AND PATIENTS

Of 736 children treated with GH because of GHD/SGA, 33 with severe FSS (life-minimum height -2.5 SD or less in both the patient and shorter parent) were included in the study. The genetic etiology was known in 5 of 33 children prior to the study [ACAN (in 2], NF1, PTPN11, and SOS1). In the remaining 28 of 33, whole-exome sequencing was performed. The results were evaluated using American College of Medical Genetics and Genomics standards and guidelines.

RESULTS

In 30 of 33 children (90%), we found at least one variant with potential clinical significance in genes known to affect growth. A genetic cause was elucidated in 17 of 33 (52%). Of these children, variants in growth plate-related genes were found in 9 of 17 [COL2A1, COL11A1, and ACAN (all in 2), FLNB, FGFR3, and IGF1R], and IGF-associated proteins were affected in 2 of 17 (IGFALS and HMGA2). In the remaining 6 of 17, the discovered genetic mechanisms were miscellaneous (TRHR, MBTPS2, GHSR, NF1, PTPN11, and SOS1).

CONCLUSIONS

Single-gene variants are frequent among families with severe FSS, with variants affecting the growth plate being the most prevalent.

The association of genetic variants in FGFR2 with osteoporosis susceptibility in Chinese Han population

Objective: The present study was conducted for exploring the influence of fibroblast growth factor 2 receptor (FGFR2) gene polymorphisms on osteoporosis occurrence risk in the Chinese population.

Methods: Polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) was conducted for the genotyping of polymorphism in 145 osteoporosis patients and 123 controls. The status of Hardy–Weinberg equilibrium was detected in the control group. Genotype and allele frequency comparison of polymorphism between the two groups was performed by χ² test, odds ratio (OR) with 95% confidence interval (95% CI) was used for the result expression about the association of FGFR2 polymorphisms with osteoporosis. Furthermore, the results were adjusted by clinical features via logistic regression analysis.

Results: AA genotype and A allele of rs2420946 were significantly associated with the increased risk of osteoporosis development adjusted by clinical features (OR = 2.238, 95% CI = 1.055–4.746; OR = 1.482, 95% CI = 1.042–2.019). Similarly, CC genotype and C allele frequencies of rs1219648 were detected the significant difference between the case and control groups (P<0.01); moreover, it was still significant by the adjustion of clinical features, which indicated that rs1219648 was significantly associated with the risk of osteoporosis occurrence (OR = 2.900, 95% CI = 1.341–6.271; OR = 1.602, 95% CI = 1.126–2.279). Haplotype T-A-C-T also obviously increased the occurrence risk of osteoporosis (OR = 1.844, 95% CI = 1.180–2.884). Besides, the significant interaction of FGFR2 polymorphisms with drinking status in osteoporosis was also found (P<0.05), especially rs2981579.

Conclusion:FGFR2 rs2420946 and rs1219648 polymorphisms may be the risk factor of osteoporosis in Chinese population. Furthermore, the interaction of FGFR2 polymorphisms with drinking may play an important role in osteoporosis etiology.

Identification of a novel mutation of FGFR3 gene in a large Chinese pedigree with hypochondroplasia by next-generation sequencing: A case report and brief literature review

RATIONALE

Hypochondroplasia (HCH) is the mildest form of chondrodysplasia characterized by disproportionate short stature, short extremities, and variable lumbar lordosis. It is caused by mutations in fibroblast growth factor receptor 3 (FGFR3) gene. Up to date, at least thirty mutations of FGFR3 gene have been found to be related to HCH. However, mutational screening of the FGFR3 gene is still far from completeness. Identification of more mutations is particularly important in diagnosis of HCH and will gain more insights into the molecular basis for the pathogenesis of HCH.

PATIENT CONCERNS

A large Chinese family consisting of 53 affected individuals with HCH phenotypes was examined.

DIAGNOSES

A novel missense mutation, c.1052C>T, in FGFR3 gene was identified in a large Chinese family with HCH. On the basis of this finding and clinical manifestations, the final diagnosis of HCH was made.

INTERVENTIONS

Next-generation sequencing (NGS) of DNA samples was performed to detect the mutation in the chondrodysplasia-related genes on the proband and her parents, which was confirmed by Sanger sequencing in the proband and most of other living affected family members.

OUTCOMES

A novel missense mutation, c.1052C>T, in the extracellular, ligand-binding domain of FGFR3 was identified in a large Chinese family with HCH. This heterozygous mutation results in substitution of serine for phenylalanine at amino acid 351 (p.S351F) and co-segregates with the phenotype in this family. Molecular docking analysis reveals that this unique FGFR3 mutation results in an enhancement of ligand-binding affinity between FGFR3 and its main ligand, fibroblast growth factor 9.

LESSONS

This novel mutation is the first mutation displaying an increase in ligand-binding affinity, therefore it may serve as a model to investigate ligand-dependent activity of FGF-FGFR complex. Our data also expanded the mutation spectrum of FGFR3 gene and facilitated clinic diagnosis and genetic counseling for this family with HCH.