Growth reference charts for children with hypochondroplasia.

Hypochondroplasia (HCH) is a rare skeletal dysplasia causing mild short stature. There is a paucity of growth reference charts for this population. Anthropometric data were collected to generate height, weight, and head circumference (HC) growth reference charts for children with a diagnosis of HCH. Mixed longitudinal anthropometric data and genetic analysis results were collected from 14 European specialized skeletal dysplasia centers. Growth charts were generated using Generalized Additive Models for Location, Scale, and Shape. Measurements for height (983), weight (896), and HC (389) were collected from 188 (79 female) children with a diagnosis of HCH aged 0-18 years. Of the 84 children who underwent genetic testing, a pathogenic variant in FGFR3 was identified in 92% (77). The data were used to generate growth references for height, weight, and HC, plotted as charts with seven centiles from 2nd to 98th, for ages 0-4 and 0-16 years. HCH-specific growth charts are important in the clinical care of these children. They help to identify if other comorbidities are present that affect growth and development and serve as an important benchmark for any prospective interventional research studies and trials.

Assessment of body fat mass, anthropometric measurement and cardiometabolic risk in children and adolescents with achondroplasia and hypochondroplasia.

Achondroplasia is a rare skeletal dysplasia characterized by rhizomelic short stature, whose prevalence is about 1 per 25,000 births. For some patients with achondroplasia, excess body weight is one of the major concerns due to an impaired linear growth. Epidemiological studies revealed a premature onset of cardiovascular or cerebrovascular events in achondroplasia. An association between obesity and cardiometabolic risk factors related to cardiovascular events remains unknown in patients with achondroplasia/hypochondroplasia. This cross-sectional study investigated anthropometric measurements, body compositions and cardiometabolic risk factors in pediatric patients with achondroplasia/hypochondroplasia. Thirty-two patients with achondroplasia and ten with hypochondroplasia aged between 1.9 and 18.7 years were enrolled in this study. Half of the participants presented at least one cardiometabolic abnormality. Elevated systolic blood pressure was the most common abnormality. None of the participants developed metabolic syndrome or type 2 diabetes mellitus. Body mass index-standard deviation score and hip/height ratio were strongly correlated with percent body fat assessed by dual energy X-ray absorptiometry although no significant association was found between anthropometric measurements or body fat mass and any cardiometabolic risk factors. No significant difference in body fat mass, as well as body mass index-standard deviation score and hip/height, was found between cardiometabolically normal group and cardiometabolically abnormal groups. These results suggest that not only weight gain and hip/height changes should be monitored but also individual cardiometabolic risk factors should be evaluated to avoid cardiometabolic events in the healthcare management of pediatric patients with achondroplasia/hypochondroplasia.

Failure to diagnose hypochondroplasia by prenatal diagnosis: a case report.

BACKGROUND: Hypochondroplasia (HCH) is a common nonlethal skeletal dysplasia caused by pathogenic variations in the fibroblast growth factor receptor 3 (FGFR3) gene, and HCH has similar clinical manifestations with achondroplasia (ACH), which can be screened during the fetal period by prenatal ultrasound testing and diagnosed by genetic testing. CASE PRESENTATION: we report the special case of a patient with obvious growth retardation and rhizomelic disproportionate short stature, accompanied by other manifestations, including an enlarged head and short hands at 1 year old. However, several multiple color ultrasound exams identified shortened limbs (< 3rd percentile), an increased biparietal diameter (> 95th percentile) and a low nasal bridge in the fetal period. Due to the high incidence rate of ACH, genetic testing for the hotspot FGFR3 gene c.1138 g > A pathogenic variations was performed immediately in the third trimester. Unfortunately, the definitive diagnosis could not be made before birth due to the negative result of hotspot gene exam. Whole exome sequencing (WES) was performed at 1 year identified FGFR3 gene c.1620C > A variations positivity, and the patient was finally diagnosed as HCH. CONCLUSION: Our report extends the understanding of the limitations of prenatal genetic diagnostic testing, especially the hot spot pathogenic variations test should be not the only clinical diagnostic basis. Moreover, this case also emphasizes that further gene analysis for patients with significant conflict between the clinical manifestation and the prenatal genetic panel examination findings should be reconducted timely to spare the family from a delayed diagnosis or a misdiagnosis.

Dental characteristics of patients with four different types of skeletal dysplasias.

OBJECTIVE: Skeletal dysplasia (SD) comprises more than 450 separate disorders. We hypothesized that their dental features would be distinctive and investigated the tooth characteristics of four patients with different SDs. MATERIAL AND METHODS: Four SD patients with molecularly confirmed diagnoses, Pt-1 acromicric dysplasia, Pt-2 hypophosphatasia and hypochondroplasia, Pt-3 cleidocranial dysplasia, and Pt-4 achondroplasia, were recruited. A tooth from each patient was evaluated for mineral density (micro-computerized tomography), surface roughness (surface profilometer), microhardness, mineral contents (energy-dispersive X-ray), and ultrastructure (scanning electron microscopy and histology), and compared with three tooth-type matched controls. RESULTS: Pt-1 and Pt-3 had several unerupted teeth. Pt-2 had an intact-root-exfoliated tooth at 2 years old. The lingual surfaces of the patients' teeth were significantly smoother, while their buccal surfaces were rougher, than controls, except for Pt-1's buccal surface. The patients' teeth exhibited deep grooves around the enamel prisms and rough intertubular dentin. Pt-3 demonstrated a flat dentinoenamel junction and Pt-2 had an enlarged pulp, barely detectable cementum layer, and ill-defined cemento-dentinal junction. Reduced microhardnesses in enamel, dentin, and both layers were observed in Pt-3, Pt-4, and Pt-1, respectively. Pt-1 showed reduced Ca/P ratio in dentin, while both enamel and dentin of Pt-2 and Pt-3 showed reduced Ca/P ratio. CONCLUSION: Each SD has distinctive dental characteristics with changes in surface roughness, ultrastructure, and mineral composition of dental hard tissues. CLINICAL RELEVANCE: In this era of precision dentistry, identifying the specific potential dental problems for each patient with SD would help personalize dental management guidelines.

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.

Sitting Height to Standing Height Ratio Reference Charts for Children in the United States.

OBJECTIVE: To create reference charts for sitting height to standing height ratio (SitHt/Ht) for children in the US, and to describe the trajectory of SitHt/Ht during puberty. STUDY DESIGN: This was a cross-sectional study using data from the 1988-1994 National Health and Nutrition Examination Survey III, a strategic random sample of the US population. Comparison between non-Hispanic White (NHW), non-Hispanic Black (NHB) and Mexican American groups was performed by ANOVA to determine if a single population reference chart could be used. ANOVA was used to compare SitHt/Ht in pre-, early, and late puberty. RESULTS: NHANES III recorded sitting height and standing height measurements in 9569 children aged 2-18 years of NHW (n = 2715), NHB (n = 3336), and Mexican American (n = 3518) ancestry. NHB children had lower SitHt/Ht than NHW and Mexican American children throughout childhood (P < .001). In both sexes, the SitHt/Ht decreased from prepuberty to early puberty and increased in late puberty. Sex-specific percentile charts of SitHt/Ht vs age were generated for NHB and for NHW and Mexican American youth combined. CONCLUSIONS: SitHt/Ht assessment can detect disproportionate short stature in children with skeletal dysplasia, but age-, sex-, and population-specific reference charts are required to interpret this measurement. NHB children in the US have significantly lower SitHt/Ht than other children, which adds complexity to interpretation. We recommend the use of standardized ancestry-specific reference charts in screening for skeletal dysplasias and have developed such charts in this study.

Use of Growth Hormone Treatment in Skeletal Dysplasia - A Review.

Skeletal dysplasias are the disorders of the skeletal and cartilaginous tissues. Short stature is the hallmark presentation. Achondroplasia is the commonest skeletal dysplasia. Growth hormone (GH) has been widely used in children with achondroplasia. Various studies have shown 1st year increase in height velocity is about 2-3cm. Apart from achondroplasia, studies have also shown positive effect of GH in hypochondroplasia children. However, in hypochondroplasia GH treatment seems to give better results when administered at puberty. Other forms of skeletal dysplasias are rare, so no conclusion on GH use in such patients can be drawn.

Novel phenotype of achondroplasia due to biallelic FGFR3 pathogenic variants.

Pathogenic variants in the fibroblast growth factor receptor 3 (FGFR3) gene are responsible for a broad spectrum of skeletal dysplasias, including achondroplasia (ACH). The classic phenotype of ACH is caused by two highly prevalent mutations, c.1138G > A and c.1138G > C (p.Gly380Arg). In the homozygous state, these variant results in a severe skeletal dysplasia, neurologic deficits, and early demise from respiratory insufficiency. Although homozygous biallelic mutations have been reported in patients with ACH in combination with hypochondroplasia or other dominant skeletal dysplasias, thus far, no cases of heterozygous biallelic pathogenic ACH-related variants in FGFR3 have been reported. We describe a novel phenotype of an infant with two ACH-related mutations in FGFR3, p.Gly380Arg and p.Ser344Cys. Discordant features from classic ACH include atypical radiographic findings, severe obstructive sleep apnea, and focal, migrating seizures. We also report the long-term clinical course of her father, who harbors the p.Ser344Cys mutation that has only been reported once previously in a Japanese patient. The phenotype of heterozygous biallelic mutations in FGFR3 associated with ACH is variable, underscoring the importance of recognition and accurate diagnosis to ensure appropriate management.

Unique association of hypochondroplasia with craniosynostosis and cleft palate in a Mexican family.

Hypochondroplasia (HCH) is a skeletal dysplasia caused by an abnormal function of the fibroblast growth factor receptor 3. Although believed to be relatively common, its prevalence and phenotype are not well established owing to its clinical, radiological, and genetic heterogeneity. Here we report on a molecularly proven HCH family with an affected father and two children. The siblings (male and female) with HCH also had craniosynostosis and cleft palate, respectively. The present report supports the conclusion that the full clinical spectrum of HCH is not completely delineated. It also suggests that secondary, as yet unknown, modifying factors can influence the final phenotype.

Further delineation of achondroplasia-hypochondroplasia complex with long-term survival.

Achondroplasia-hypochondroplasia (ACH-HCH) complex is caused by the presence of two different pathogenic variants in each allele of FGFR3 gene. Only four patients with confirmed molecular diagnoses have been reported to date, and the phenotype has not been fully defined. Here, we describe a Mexican patient with a confirmed molecular diagnosis of ACH-HCH complex. This patient exhibits intellectual disability, has a history of seizures, experienced multiple cardiorespiratory complications during early childhood, and required foramen magnum decompression. However, he now shows a stable health condition with long-term survival (current age, 18 years). This case is particularly relevant to our understanding of ACH-HCH complex and for the genetic counseling of couples who are affected with ACH or HCH.

Achondroplasia: Development, pathogenesis, and therapy.

Autosomal dominant mutations in fibroblast growth factor receptor 3 (FGFR3) cause achondroplasia (Ach), the most common form of dwarfism in humans, and related chondrodysplasia syndromes that include hypochondroplasia (Hch), severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN), and thanatophoric dysplasia (TD). FGFR3 is expressed in chondrocytes and mature osteoblasts where it functions to regulate bone growth. Analysis of the mutations in FGFR3 revealed increased signaling through a combination of mechanisms that include stabilization of the receptor, enhanced dimerization, and enhanced tyrosine kinase activity. Paradoxically, increased FGFR3 signaling profoundly suppresses proliferation and maturation of growth plate chondrocytes resulting in decreased growth plate size, reduced trabecular bone volume, and resulting decreased bone elongation. In this review, we discuss the molecular mechanisms that regulate growth plate chondrocytes, the pathogenesis of Ach, and therapeutic approaches that are being evaluated to improve endochondral bone growth in people with Ach and related conditions. Developmental Dynamics 246:291-309, 2017. © 2016 Wiley Periodicals, Inc.

Foramen magnum compression in Coffin-Lowry syndrome: A case report.

Coffin-Lowry syndrome (CLS) is a rare genetic disorder inherited in an X-linked dominant pattern. Common manifestations include intellectual disability, growth retardation, dysmorphic facial features, and variable skeletal anomalies. Here we report a patient who first presented with episodes of apparent life-threatening events (ALTE) found to be caused by hydrocephalus and brainstem compression at the foramen magnum. Together with his small size, short limbs and fingers, and facial appearance, the narrowing of the foramen magnum lead to the initial clinical misdiagnosis of hypochondroplasia. Subsequent evaluation and testing lead to the correct diagnosis of CLS. This case demonstrates the variability in presentation of CLS, and that skeletal findings may be misleading in infancy. © 2017 Wiley Periodicals, Inc.

Mild achondroplasia/hypochondroplasia with acanthosis nigricans, normal development, and a p.Ser348Cys FGFR3 mutation.

Pathogenic allelic variants in the fibroblast growth factor receptor 3 (FGFR3) gene have been associated with a number of phenotypes including achondroplasia, hypochondroplasia, thanatophoric dysplasia, Crouzon syndrome with acanthosis nigricans (Crouzonodermoskeletal syndrome), and SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans). Crouzon syndrome with acanthosis nigricans is caused by the pathogenic variant c.1172C>A (p.Ala391Glu) in the FGFR3 gene. The p.Lys650Thr pathogenic variant in FGFR3 has been linked to acanthosis nigricans without significant craniofacial or skeletal abnormalities. Recently, an infant with achondroplasia and a novel p.Ser348Cys FGFR3 mutation was reported. We describe the clinical history of an 8-year-old child with a skeletal dysplasia in the achondroplasia-hypochondroplasia spectrum, acanthosis nigricans, typical development, and the recently described p.Ser348Cys FGFR3 mutation.

Criteria for radiologic diagnosis of hypochondroplasia in neonates.

BACKGROUND: A radiologic diagnosis of hypochondroplasia is hampered by the absence of age-dependent radiologic criteria, particularly in the neonatal period. OBJECTIVE: To establish radiologic criteria and scoring system for identifying neonates with fibroblast growth factor receptor 3 (FGFR3)-associated hypochondroplasia. MATERIALS AND METHODS: This retrospective study included 7 hypochondroplastic neonates and 30 controls. All subjects underwent radiologic examination within 28 days after birth. We evaluated parameters reflecting the presence of (1) short ilia, (2) squared ilia, (3) short greater sciatic notch, (4) horizontal acetabula, (5) short femora, (6) broad femora, (7) metaphyseal flaring, (8) lumbosacral interpedicular distance narrowing and (9) ovoid radiolucency of the proximal femora. RESULTS: Only parameters 1, 3, 4, 5 and 6 were statistically different between the two groups. Parameters 3, 5 and 6 did not overlap between the groups, while parameters 1 and 4 did. Based on these results, we propose a scoring system for hypochondroplasia. Two major criteria (parameters 3 and 6) were assigned scores of 2, whereas 4 minor criteria (parameters 1, 4, 5 and 9) were assigned scores of 1. All neonates with hypochondroplasia in our material scored ≥6. CONCLUSION: Our set of diagnostic radiologic criteria might be useful for early identification of hypochondroplastic neonates.

Low bone mineral density in achondroplasia and hypochondroplasia.

BACKGROUND: Achondroplasia (ACH) and hypochondroplasia (HCH) are the most common form of short-limb skeletal dysplasias caused by activated fibroblast growth factor receptor 3 (FGFR3) signaling. Although decreased bone mass was reported in gain-of-function mutation in Fgfr3 mice, both disorders have never been described as osteoporotic. In the present study, we evaluated bone mineral density (BMD) in ACH and HCH patients. METHODS: We measured spinal BMD (L1-L4) in 18 ACH and four HCH patients with an average age of 19.8 ± 7.5 years (range, 10-33 years). BMD Z-score in each individual was calculated for normalizing age and gender. Correlation between body mass index (BMI) and BMD was analyzed. Moreover, BMD and Z-score were compared between ACH patients and HCH patients. RESULTS: The average BMD of ACH/HCH patients was 0.805 ± 0.141 g/cm(2) (range, 0.554-1.056 g/cm(2) ), resulting in an average Z-score of -1.1 ± 0.8 (range, -2.4 to 0.6) of the standard value. A slightly positive correlation was observed between BMI and BMD (r = 0.45; P = 0.13). There was no significant difference in BMD and Z-score between ACH and HCH patients. CONCLUSION: Spinal BMD was reduced in ACH/HCH patients, and was mildly correlated with individual BMI. We should carefully monitor BMD and examine osteoporosis-related symptoms in adolescent and adult ACH/HCH patients. © 2016 Japan Pediatric Society.

Improvement of molecular-genetic diagnostics of the most common skeletal dysplasias.

UNLABELLED: achondroplasia (ACH) and hypochondroplasia (HCH) into the routine practice. BACKGROUND: Both disorders are usually caused by de novo gain-of-function type mutations in FGFR3 gene encoding the fibroblast growth factor receptor 3, which plays an important role in the metabolism of connective tissues. More than 99% of ACH cases are caused by the glycine-to-arginine substitution at codon 380 and about 70% of HCH cases result from the asparagine-to-lysine/-serine/-threonine substitutions at codon 540 in the consequence of the four different possible nucleotide changes occurred at the same codon. METHODS: Exons 10 and 13 of the FGFR3 gene were analysed by PCR-RFLP and sequencing analysis. The exon 13 sequencing was necessary for mutation type specification. RESULTS: We confirmed the diagnosis of ACH due to 1138G→A transition in 7 patients and we identified 1620C→A transversion responsible for HCH in 2 patients. CONCLUSION: Due to serious limitations in recently used methods, we had to modify the molecular-genetic diagnostics approach. We developed the reliable diagnostics and made it available for achondroplasia and hypochondroplasia suspected patients (Tab. 1, Ref. 5, Ref. 17).

Homozygous N540K hypochondroplasia--first report: radiological and clinical features.

We describe a 16-month-old male with N540K homozygous mutation in the FGFR3 gene who showed a more severe phenotype than hypochondroplasia (HCH). To our knowledge, a homozygous state for this mutation causing HCH has not been reported before. The clinical and radiological characteristics of our patient represent an intermediate condition between achondroplasia and achondroplasia/hypochondroplasia compound heterozygosity. This case represents a new expression of FGFR3 spectrum and it is of considerable importance for the genetic counseling in cases where both parents are affected with HCH.

Prenatal ultrasound and MRI findings of temporal and occipital lobe dysplasia in a twin with achondroplasia.

Thanatophoric dysplasia, hypochondroplasia and achondroplasia are all caused by FGFR3 (fibroblast growth factor receptor 3) mutations. Neuropathological findings of temporal lobe dysplasia are found in thanatophoric dysplasia, and temporal and occipital lobe abnormalities have been described recently in brain imaging studies of children with hypochondroplasia. We describe twins discordant for achondroplasia, in one of whom the prenatal diagnosis was based on ultrasound and fetal MRI documentation of temporal and occipital lobe abnormalities characteristic of hypochondroplasia, in addition to the finding of short long bones. Despite the intracranial findings suggestive of hypochondroplasia, achondroplasia was confirmed following postnatal clinical and genetic testing. These intracranial abnormalities have not been previously described in a fetus with achondroplasia.

Children with short-limbed short stature in pediatric endocrinological services in Japan.

Short-limbed short stature is a heterogeneous condition that can result from many diseases such as bone disorder, metabolic disease, and multiple malformation syndrome. We conducted a questionnaire survey of council members of the Japanese Society of Pediatric Endocrinology and doctors of affiliated hospitals in 2010 to investigate short-limbed short stature. Among 91 hospitals, responses were obtained from 61 hospitals (67% response rate). This study also examined data of 193 short-limbed short stature patients, among whom FGFR3-related chondrodysplasia such as achondroplasia (n = 109; 56.5%) was found the most frequently. Second to achondroplasia, hypochondroplasia (n = 47; 24.4%) was the most frequently observed. Along with achondroplasia and hypochondroplasia, 31 patients with disorders of 13 other kinds and six undiagnosed patients were identified. Genetic testing for hypochondroplasia was conducted for only 27.7% of all hypochondroplasia patients, although hypochondroplasia is a heterogeneous condition with many causes, only one of which is FGFR3 mutation. We conducted a genetic analysis of 25 patients who had been clinically diagnosed as having "hypochondroplasia". In these patients, other diseases such as acromicric dysplasia, geleophysic dysplasia, and Aarskog-Scott syndrome were included in addition to FGFR3-related hypochondroplasia (n = 10). Clinical diagnosis of each disorder causing short-limbed short stature is difficult. Therefore, not only clinical diagnosis but also genetic diagnosis play an important role in the diagnosis of short-limb short stature. Diagnostic strategies must be created for each disorder.

Frequency of the allelic variant c.1150T > C in exon 10 of the fibroblast growth factor receptor 3 (FGFR3) gene is not increased in patients with pathogenic mutations and related chondrodysplasia phenotypes.

Mutations in the FGFR3 gene cause the phenotypic spectrum of FGFR3 chondrodysplasias ranging from lethal forms to the milder phenotype seen in hypochondroplasia (Hch). The p.N540K mutation in the FGFR3 gene occurs in ∼70% of individuals with Hch, and nearly 30% of individuals with the Hch phenotype have no mutations in the FGFR3, which suggests genetic heterogeneity. The identification of a severe case of Hch associated with the typical mutation c.1620C > A and the occurrence of a c.1150T > C change that resulted in a p.F384L in exon 10, together with the suspicion that this second change could be a modulator of the phenotype, prompted us to investigate this hypothesis in a cohort of patients. An analysis of 48 patients with FGFR3 chondrodysplasia phenotypes and 330 healthy (control) individuals revealed no significant difference in the frequency of the C allele at the c.1150 position (p = 0.34). One patient carrying the combination `pathogenic mutation plus the allelic variant c.1150T > C' had a typical achondroplasia (Ach) phenotype. In addition, three other patients with atypical phenotypes showed no association with the allelic variant. Together, these results do not support the hypothesis of a modulatory role for the c.1150T > C change in the FGFR3 gene.