Relevance of Extending FGFR3 Gene Analysis in Osteochondrodysplasia to Non-Coding Sequences: A Case Report

Skeletal dysplasia, also called osteochondrodysplasia, is a category of disorders affecting bone development and children's growth. Up to 552 genes, including fibroblast growth factor receptor 3 (FGFR3), have been implicated by pathogenic variations in its genesis. Frequently identified causal mutations in osteochondrodysplasia arise in the coding sequences of the FGFR3 gene: c.1138G>A and c.1138G>C in achondroplasia and c.1620C>A and c.1620C>G in hypochondroplasia. However, in some cases, the diagnostic investigations undertaken thus far have failed to identify the causal anomaly, which strengthens the relevance of the diagnostic strategies being further refined. We observed a Caucasian adult with clinical and radiographic features of achondroplasia, with no common pathogenic variant. Exome sequencing detected an FGFR3(NM_000142.4):c.1075+95C>G heterozygous intronic variation. In vitro studies showed that this variant results in the aberrant exonization of a 90-nucleotide 5' segment of intron 8, resulting in the substitution of the alanine (Ala359) for a glycine (Gly) and the in-frame insertion of 30 amino acids. This change may alter FGFR3's function. Our report provides the first clinical description of an adult carrying this variant, which completes the phenotype description previously provided in children and confirms the recurrence, the autosomal-dominant pathogenicity, and the diagnostic relevance of this FGFR3 intronic variant. We support its inclusion in routinely used diagnostic tests for osteochondrodysplasia. This may increase the detection rate of causal variants and therefore could have a positive impact on patient management. Finally, FGFR3 alteration via non-coding sequence exonization should be considered a recurrent disease mechanism to be taken into account for new drug design and clinical trial strategies.

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.

What the pediatric endocrinologist needs to know about skeletal dysplasia, a primer

Children with skeletal dysplasia are frequently referred to pediatric endocrinologists due to short stature. These children may present with disproportionate growth or medical histories that point to a skeletal dysplasia. This primer will discuss when to be concerned about skeletal dysplasia, the initial steps in evaluation for a skeletal dysplasia, and new therapies that are either recently approved or in development.

Clinical and radiologic evaluation of a Turkish family with hypochondroplasia and a rare FGFR3 variant

OBJECTIVES

Hypochondroplasia (HCH) is characterized by disproportionate short stature and regarded as a milder form of achondroplasia (ACH), which is another skeletal dysplasia, both caused by variants in fibroblast growth factor receptor 3 (FGFR3) gene. HCH diagnosis is based on the clinical features and skeletal survey findings. The most common FGFR3 variant in HCH affects the codon 540, leading to substitution of asparagine with lysine in about 70% of patients.

CASE PRESENTATION

Herein, we described the clinical and radiographical manifestations of HCH in affected members of a Turkish family with very rare Asn540Thr (c.1619A>C) variant within hot spot of the gene for this condition.

CONCLUSIONS

This is a very rarely reported variant in the literature and this report is the first case with this variant in Turkish population. The report also presents the phenotypic variability within a family with the same variant, which is inherent to HCH.

Inconvenience and adaptation in Japanese adult achondroplasia and hypochondroplasia: A cross-sectional study

The health-related quality of life is reduced in patients with achondroplasia (ACH) and hypochondroplasia (HCH); however, the detailed inconveniences in the daily living and individual adaptations have not been elucidated. This study aimed to evaluate the inconvenience and adaptation in patients with ACH/HCH. A cross-sectional study was conducted in patients with ACH/HCH aged 20 yr or older. Questionnaires were sent to 567 patients (described 86) with a medical history at the co-authors’ institutions or who were registered at the patients’ association with ACH in Japan. The questionnaire included a free description format for the inconveniences and adaptations in daily living; a content analysis was performed. The recorded inconveniences included 148 physical, 84 mental, and 52 social problems. Patients who underwent spine surgery had significantly more recorded physical problems than those who did not (p < 0.05). Pain and numbness were significantly higher in patients aged ≥ 50 yr (p < 0.05). The 160 and 1 adaptations were for physical and social problems, respectively. No patient adaptation was found for mental health problems. Individual adaptations by ACH/HCH patients can improve only some aspects of physical and social problems. Multilateral social support is needed to resolve patients’ issues.

High-Resolution Melting Analysis for Rapid Detection of Mutations in Patients with FGFR3-Related Skeletal Dysplasias

Background: Mutations in the fibroblast growth factor receptor 3 (FGFR3) gene are related to skeletal dysplasias (SDs): acondroplasia (ACH), hypochodroplasia (HCH) and type I (TDI) and II (TDII) tanatophoric dysplasias. This study was designed to standardize and implement a high-resolution melting (HRM) technique to identify mutations in patients with these phenotypes. Methods: Initially, FGFR3 gene segments from 84 patients were PCR amplified and subjected to Sanger sequencing. Samples from 29 patients positive for mutations were analyzed by HRM. Results: Twelve of the patients FGFR3 mutations had ACH (six g.16081 G > A, three g.16081 G > C and three g.16081 G > A + g.16002 C > T); thirteen of patients with HCH had FGFR3 mutations (eight g.17333 C > A, five g.17333 C > G and five were negative); and four patients with DTI had FGFR3 mutations (three g.13526 C > T and one g.16051G > T and two patients with DTII (presented mutation g.17852 A > G). When analyzing the four SDs altogether, an overlap of the dissociation curves was observed, making genotyping difficult. When analyzed separately, however, the HRM analysis method proved to be efficient for discriminating among the mutations for each SD type, except for those patients carrying additional polymorphism concomitant to the recurrent mutation. Conclusion: We conclude that for recurrent mutations in the FGFR3 gene, that the HRM technique can be used as a faster, reliable and less expensive genotyping routine for the diagnosis of these pathologies than Sanger sequencing.

Extensive Limb Lengthening for Achondroplasia and Hypochondroplasia

Extensive limb lengthening (ELL) was completed in 75 patients: 66 achondroplasia and 9 hypochondroplasia. The average lengthening was 27 cm for achondroplasia (12–40 cm) and 17 cm for hypochondroplasia (range 10–25 cm). There were 48 females and 27 males. Lengthening was done either by 2-segment (14 patients; both tibias and/or both femurs) or by 4-segment lengthenings (64 patients; both femurs and tibias at the same time). Most patients also had bilateral humeral lengthening. Patients had 2 or 3 lower limb lengthenings and one humeral lengthening. Lengthenings were either juvenile-onset (31), adolescent-onset (38) or adult-onset (6). The average age at final follow-up was 26 years old (range 17–43 years). There were few permanent sequelae of complications. The most serious was one paraparesis. All patients returned to activities of normal living and only one was made worse by the surgery (paraparesis). This is the first study to show that ELL can lead to an increase of height into the normal height range. Previous studies showed mean increases of height of up to 20 cm, while this study consistently showed an average increase of 30 cm (range 15–40 cm) for juvenile-onset and mean increase of 26 cm (range 15–30 cm) for adolescent-onset. This results in low normal height at skeletal maturity for males and females. The adult-onset had a mean increase of 16.8 (range 12–22 cm). This long-term follow-up study shows that ELL can be done safely even with large lengthenings and that 4-segment lengthening may offer advantages over 2-segment lengthening. While all but the more recent cases were performed using external fixation, implantable limb lengthening promises to be an excellent alternative and perhaps an improvement.

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.

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.

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.

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.

FGFR3-related hypochondroplasia: longitudinal growth in 57 children with the p.Asn540Lys mutation

Background Children with hypochondroplasia (HCH), who have FGFR3 mutations c.1620C>A or c.1620C>G (p.Asn540Lys) appear to have a more severe phenotype than those with HCH without these mutations. We describe the change in height, leg length and body proportions in a retrospective cohort of children with HCH related-p.Asn540Lys mutation and we compared them with Argentine population. Methods Anthropometric measurements were initially taken and followed up by the same observer, with standardized techniques. Sitting height/height and head circumference/height ratio were calculated as a body disproportion indicator. In order to make a comparison with the Argentine population height average, centiles of height, leg length and body proportions were estimated by the LMS method. Results The sample consisted of 57 HCH children (29 males and 28 females) between the ages of 0-18 years. The median (interquartile range) number of measurements per child was 8 (4.3, 13) for height, 7 (4, 12) for sitting height and 7.5 (4, 12.8) for head circumference. Leg length increased from 17 cm at birth to approximately 54 cm in adolescents, 25 cm shorter than the leg length in non-HCH populations. Sitting height increased from 39 cm at birth to 81 cm in adolescents, 7 cm below mean in non-HCH adolescents. Mean (range) adult height were 143.6 cm (131-154.5) and 130.8 cm (124-138) for males and females, respectively. Conclusions The disharmonic growth between the less affected trunk and the severely affected limbs determine body disproportion in HCH.

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.

Acanthosis nigricans in a Japanese boy with hypochondroplasia due to a K650T mutation in FGFR3

Acanthosis nigricans (AN) is observed in some cases of skeletal dysplasia. However, AN has occasionally been reported in patients with hypochondroplasia (HCH), and a clinical diagnosis is sometimes difficult when its physical and radiological features are mild. Mutations in the gene encoding the fibroblast growth factor receptor 3 (FGFR3) have been identified as the cause of some types of skeletal dysplasia, which is diagnostically useful. Here, we report the case of a 3-yr-old Japanese boy who presented with AN. His height, weight, head circumference, and arm span were 91.7 cm (–1.95 SD), 16.3 kg, 54.0 cm (+2.6 SD), and 88.0 cm, respectively. In addition to the AN, he also exhibited a mild height deficit and macrocephaly, which prompted a search for FGFR3 mutations, although no skeletal disproportion, exaggerated lumbar lordosis, or facial dysmorphism was observed, and only slight radiological abnormalities were noted. A definitive diagnosis of HCH was made based on FGFR3 gene analysis, which detected a heterozygous K650T mutation. Insulin insensitivity was not found to have contributed to the development of AN. In individuals with AN, careful assessments for symptoms of HCH are important, regardless of the presence or absence of a short stature, and FGFR3 gene analysis is recommended in such cases.

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.

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.

Height outcome of short children with hypochondroplasia after recombinant human growth hormone treatment: a meta-analysis

Hypochondroplasia (HCH) is a genetic skeletal dysplasia, characterized by rhizomelic short height (Ht) with facial dysmorphology and lumbar hyperlordosis. Albeit there are concerns that HCH children may not achieve optimal long-term outcome in response to recombinant human growth hormone (rhGH), anecdotal experiences suggested at least short-term Ht improvement. After thorough search of published studies, meta-analysis of rhGH use in HCH children was performed. In 113 HCH children, rhGH administration (median 0.25 mg/kg/week) progressively improved Ht pattern with 12 months catch-up growth (p < 0.0001). Then, Ht improvement resulted constant until 36 months (p < 0.0001), but stature remained subnormal. While bone age chronologically progressed, no serious adverse events were reported. In conclusion, our meta-analysis indicates that rhGH treatment progressively improved Ht outcome of HCH subjects.

Whole-exome sequencing and whole genome re-sequencing for prenatal diagnosis of achondroplasia

OBJECTIVE

To investigate the feasibility of whole exome sequencing (WES) and whole genome re-sequencing (WGS) in the prenatal diagnosis of achondroplasia (ACH).

METHODS

Eleven highly suspected with ACH or hypochondroplasia (HCH) fetuses and their parents were enrolled in this study. Routine prenatal examinations were carried out in all pregnant women. WGS was performed for the detection of copy number variation (CNV). WES was conducted to determine the mutation of fibroblast growth factor receptor 3 (FGFR3) gene in one special family with rickets and dwarfism. Moreover, all subjects were performed Sanger sequencing for the screening of high frequent mutation sites in FGFR3 gene.

RESULTS

For ultrasound (US) examination, short femur was noted in all fetuses with FL less than 4SD and 2SD in 8 cases and one case compared with those of normal gestational weeks, respectively. CNV abnormality was identified in 5 cases, including heterozygous deletion in 4 cases and heterozygous duplication in one case. Among these variation, one case was acknowledged to be pathogenic, one case was identified as genomic polymorphism, while the pathogenicity remained unknown in other 3 cases. For the exome and Sanger sequencing, heterozygous mutation p.Tyr278Cys (833A>G) was noted in the fetus and husband of the special family, while homozygous c.1959+19G>A mutation was identified in another case.

CONCLUSION

Multiple sequencing technologies may provide an additional diagnostic tool and facilitates genetic counseling in the patients with ACH. Further improvement of gene sequencing should be done in the prenatal diagnosis for the mutant screening in other genes.

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

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).

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.

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.

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.

FGFR3 mutation frequency in 324 cases from the International Skeletal Dysplasia Registry

Fibroblast growth factor receptor 3 (FGFR3) is the only gene known to cause achondroplasia (ACH), hypochondroplasia (HCH), and thanatophoric dysplasia types I and II (TD I and TD II). A second, as yet unidentified, gene also causes HCH. In this study, we used sequencing analysis to determine the frequency of FGFR3 mutations for each phenotype in 324 cases from the International Skeletal Dysplasia Registry (ISDR). Our data suggest that there is a considerable overlap of genotype and phenotype between ACH and HCH. Thus, it is important to test for mutations found in either disorder when ACH or HCH is suspected. Only two of 29 cases with HCH did not have an identified mutation in FGFR3, much less than previously reported. We recommend testing other mutations in FGFR3, instead of just the common HCH mutation, p.Asn540Lys. The mutation frequency for TD I and TD II in the largest series of cases to date are also reported. This study provides valuable information on FGFR3 mutation frequency of four skeletal dysplasias for clinical diagnostic laboratories and clinicians.

Treatment of varus deformities of the lower limbs in patients with achondroplasia and hypochondroplasia

Angular deformities of the lower limbs are a common clinical problem encountered in pediatric orthopaedic practices particularly in patients with osteochondrodysplasias. The varus deformity is more common than the valgus deformity in achondroplasia and hypochondroplasia patients because of the unusual growth of the fibulae than that of the tibiae. We retrospectively reviewed six patients (four patients with achondroplasia and two patients with hypochondroplsia) with relevant limb deformities due to the above-mentioned entities. All patients manifested significant varus deformity of the lower limbs. Detailed phenotypic characterization, radiologic and genetic testing was carried out as baseline diagnostic tool. We described the re-alignment procedures, which have been applied accordingly. Therefore, bilateral multi-level procedures, multi-apical planning and limb lengthening have been successfully applied. While recognition of the underlying syndromic association in patients who are manifesting angular deformities is the baseline for proper orthopaedic management, this paper demonstrates how to evaluate and treat these complex patients.

Hypochondroplasia in a child with 1620C>G (Asn540Lys) mutation in FGFR3

Hypochondroplasia (HCP) is an autosomal dominant skeletal dysplasia characterized by short extremities, short stature and lumbar lordosis, usually exhibiting a phenotype similar to but milder than achondroplasia (ACP). Fibroblast growth factor receptor 3 gene (FGFR3) mutations in the germline are well-known causes of skeletal syndromes. FGFR3 is a negative regulator of bone growth and all mutations in FGFR3 are gain-of-function mutations that lead to skeletal dysplasias. We report a child who presented with short stature, a relatively long trunk, short legs, short arm span, radiographic evidence of HCP and mild mental retardation. Genetic analysis revealed a heterozygous 1620C>G (Asn540Lys) mutation in FGFR3. To our knowledge, ours is the first case report of HCP with a heterozygous 1620C>G (Asn540Lys) mutation in Turkey.