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.

Review of published 467 achondroplasia patients: clinical and mutational spectrum.

AIM: Achondroplasia is the most common of the skeletal dysplasias that cause fatal and disabling growth and developmental disorders in children, and is caused by a mutation in the fibroblast growth factor receptor, type 3 gene(FGFR3). This study aims to analyse the clinical characteristics and gene mutations of ACH to accurately determine whether a patient has ACH and to raise public awareness of the disease. METHODS: The database of Pubmed, Cochrane Library, Wanfang and CNKI were searched with terms of "Achondroplasias" or "Skeleton-Skin-Brain Syndrome" or "Skeleton Skin Brain Syndrome" or "ACH" and "Receptor, Fibroblast Growth Factor, Type 3" or "FGFR3". RESULTS: Finally, four hundred and sixty-seven patients with different FGFR3 mutations were enrolled. Of the 138 patients with available gender information, 55(55/138, 40%) were female and 83(83/138, 60%) were male. Among the patients with available family history, 47(47/385, 12%) had a family history and 338(338/385, 88%) patients were sporadic. The age of the patients ranged from newborn babies to 36 years old. The mean age of their fathers was 37 ± 7 years (range 31-53 years). Patients came from 12 countries and 2 continents, with the majority being Asian (383/432, 89%), followed by European (49/432, 11%). Short stature with shortened arms and legs was found in 112(112/112) patients, the abnormalities of macrocephaly in 94(94/112) patients, frontal bossing in 89(89/112) patients, genu valgum in 64(64/112) patients and trident hand were found in 51(51/112) patients. The most common mutation was p.Gly380Arg of the FGFR3 gene, which contained two different base changes, c.1138G > A and c.1138G > C. Ten rare pathogenic mutations were found, including c.831A > C, c.1031C > G, c.1043C > G, c.375G > T, c.1133A > G, c.1130T > G, c.833A > G, c.649A > T, c.1180A > T and c.970_971insTCTCCT. CONCLUSION: ACH was caused by FGFR3 gene mutation, and c.1138G > A was the most common mutation type. This study demonstrates the feasibility of molecular genetic testing for the early detection of ACH in adolescents with short stature, trident hand, frontal bossing, macrocephaly and genu valgum.

Cell-based screen identifies porphyrins as FGFR3 activity inhibitors with therapeutic potential for achondroplasia and cancer.

Overactive fibroblast growth factor receptor 3 (FGFR3) signaling drives pathogenesis in a variety of cancers and a spectrum of short-limbed bone dysplasias, including the most common form of human dwarfism, achondroplasia (ACH). Targeting FGFR3 activity holds great promise as a therapeutic approach for treatment of these diseases. Here, we established a receptor/adaptor translocation assay system that can specifically monitor FGFR3 activation, and we applied it to identify FGFR3 modulators from complex natural mixtures. An FGFR3-suppressing plant extract of Amaranthus viridis was identified from the screen, and 2 bioactive porphyrins, pheophorbide a (Pa) and pyropheophorbide a, were sequentially isolated from the extract and functionally characterized. Further analysis showed that Pa reduced excessive FGFR3 signaling by decreasing its half-life in FGFR3-overactivated multiple myeloma cells and chondrocytes. In an ex vivo culture system, Pa alleviated defective long bone growth in humanized ACH mice (FGFR3ACH mice). Overall, our study presents an approach to discovery and validation of plant extracts or drug candidates that target FGFR3 activation. The compounds identified by this approach may have applications as therapeutics for FGFR3-associated cancers and skeletal dysplasias.

Functional characterization of a rare pathogenic variant c.875G > A, p.(Cys292Tyr) in COMP.

BACKGROUND: The protein encoded by the cartilage oligomeric matrix protein (COMP) gene is a noncollagenous extracellular matrix (ECM) protein that is important for chondrocyte formation and growth. Variations in the COMP gene cause pseudoachondroplasia (PSACH), which is mainly characterized by short-limbed dwarfing in the clinic. AIMS: To characterize the function of a rare pathogenic variant in the COMP gene (c.875G > A, p.Cys292Tyr). MATERIALS & METHODS: We performed 3D structural analysis, in vitro expression analysis, and immunofluorescence to characterize the effects of the variant on protein structure, expression, and cellular localization respectively. RESULTS: Variation modeling showed that the interactions between amino acids were changed after the variation, and there were 31 changes in the secondary structure of mutant COMP (MT-COMP). Western blot showed that the intracellular quantity of MT-COMP was higher than the wild-type COMP (WT-COMP). Cellular immunofluorescence results showed that WT-COMP was less abundant and homogenously distributed in cells, while the MT-COMP accumulated in the cytoplasm. DISCUSSION: Herein, we report a variant of COMP in a Chinese family with PSACH. We have shown that the rare missense variant, COMP c.875G > A, previously reported in ClinVar and identified in our patient, results in excessive accumulation of mutant protein in the cytoplasm, and is therefore pathogenic. CONCLUSION: Through in silico and experimental analyses, we provide evidence that COMP c.875G > A is the likely cause of PSACH in a Chinese family.

Molecular and Genetic Mechanisms of Spinal Stenosis Formation: Systematic Review.

Spinal stenosis (SS) is a multifactorial polyetiological condition characterized by the narrowing of the spinal canal. This condition is a common source of pain among people over 50 years old. We perform a systematic review of molecular and genetic mechanisms that cause SS. The five main mechanisms of SS were found to be ossification of the posterior longitudinal ligament (OPLL), hypertrophy and ossification of the ligamentum flavum (HLF/OLF), facet joint (FJ) osteoarthritis, herniation of the intervertebral disc (IVD), and achondroplasia. FJ osteoarthritis, OPLL, and HLF/OLFLF/OLF have all been associated with an over-abundance of transforming growth factor beta and genes related to this phenomenon. OPLL has also been associated with increased bone morphogenetic protein 2. FJ osteoarthritis is additionally associated with Wnt/ß-catenin signaling and genes. IVD herniation is associated with collagen type I alpha 1 and 2 gene mutations and subsequent protein dysregulation. Finally, achondroplasia is associated with fibroblast growth factor receptor 3 gene mutations and fibroblast growth factor signaling. Although most publications lack data on a direct relationship between the mutation and SS formation, it is clear that genetics has a direct impact on the formation of any pathology, including SS. Further studies are necessary to understand the genetic and molecular changes associated with SS.

Thoracolumbar stenosis and neurologic symptoms: Quantitative MRI in achondroplasia.

BACKGROUND AND PURPOSE: Whole-spine magnetic resonance imaging (MRI) studies, to identify structural abnormalities associated with the development of symptomatic spinal stenosis in achondroplasia. METHODS: Forty-two subjects with achondroplasia were grouped into four age-related categories. Congenital spinal deformities (vertebral body and disc height, interpedicular distance), acquired spinal degenerative changes, thoracic kyphotic (TK) angle, thoracolumbar kyphotic (TLK) angle, spinal canal widths were evaluated by MRI. RESULTS: Patients in the first three groups were asymptomatic and younger (group 1: 4.4 ± 0.78 years; group 2: 8.18 ± 0.60 years; group 3: 10.95 ± 0.93 years) than the symptomatic group (group 4: 23 ± 1.30 years). Patients showed height of vertebral bodies, whole canal width, and average lumbar interpedicular distance reduced. Discs degeneration was more pronounced in the lumbar region and in symptomatic adult patients. TK and TLK angles showed a positive correlation with age (p < .05, r = .42; p < .05, r = .41), whereas thoracic and thoracolumbar canal width had a negative correlation (p < .05, r = -.69; p < .05, r = -.58). A negative correlation between lumbar discs degeneration and canal width was found only at L1-L3 level (p < .05, r = -.35). At L1-L3, the canal width cutoff value of .59 allowed the differentiation between asymptomatic and symptomatic patients (area under the curve of .966, p < .0001). CONCLUSION: In achondroplasia, the spinal canal narrowing, due to accelerated degenerative changes, is a predisposing factor of symptomatic lumbar spinal stenosis. Lumbar canal MRI is a helpful tool to detect the risk of the development of neurological symptoms; in adult patients, a stenosis higher than 60% of upper lumbar canal could be a critical value for the onset of neurological symptoms.

A Novel Splicing Variant of COL2A1 in a Fetus with Achondrogenesis Type II: Interpretation of Pathogenicity of In-Frame Deletions.

Achondrogenesis type II (ACG2) is a lethal skeletal dysplasia caused by dominant pathogenic variants in COL2A1. Most of the variants found in patients with ACG2 affect the glycine residue included in the Gly-X-Y tripeptide repeat that characterizes the type II collagen helix. In this study, we reported a case of a novel splicing variant of COL2A1 in a fetus with ACG2. An NGS analysis of fetal DNA revealed a heterozygous variant c.1267-2_1269del located in intron 20/exon 21. The variant occurred de novo since it was not detected in DNA from the blood samples of parents. We generated an appropriate minigene construct to study the effect of the variant detected. The minigene expression resulted in the synthesis of a COL2A1 messenger RNA lacking exon 21, which generated a predicted in-frame deleted protein. Usually, in-frame deletion variants of COL2A1 cause a phenotype such as Kniest dysplasia, which is milder than ACG2. Therefore, we propose that the size and position of an in-frame deletion in COL2A1 may be relevant in determining the phenotype of skeletal dysplasia.

Joint Degeneration in a Mouse Model of Pseudoachondroplasia: ER Stress, Inflammation, and Block of Autophagy.

Pseudoachondroplasia (PSACH), a short limb skeletal dysplasia associated with premature joint degeneration, is caused by misfolding mutations in cartilage oligomeric matrix protein (COMP). Here, we define mutant-COMP-induced stress mechanisms that occur in articular chondrocytes of MT-COMP mice, a murine model of PSACH. The accumulation of mutant-COMP in the ER occurred early in MT-COMP articular chondrocytes and stimulated inflammation (TNFα) at 4 weeks, and articular chondrocyte death increased at 8 weeks while ER stress through CHOP was elevated by 12 weeks. Importantly, blockage of autophagy (pS6), the major mechanism that clears the ER, sustained cellular stress in MT-COMP articular chondrocytes. Degeneration of MT-COMP articular cartilage was similar to that observed in PSACH and was associated with increased MMPs, a family of degradative enzymes. Moreover, chronic cellular stresses stimulated senescence. Senescence-associated secretory phenotype (SASP) may play a role in generating and propagating a pro-degradative environment in the MT-COMP murine joint. The loss of CHOP or resveratrol treatment from birth preserved joint health in MT-COMP mice. Taken together, these results indicate that ER stress/CHOP signaling and autophagy blockage are central to mutant-COMP joint degeneration, and MT-COMP mice joint health can be preserved by decreasing articular chondrocyte stress. Future joint sparing therapeutics for PSACH may include resveratrol.

Evaluating the results of long tubular bone distraction with an advanced rod monolateral external fixator for achondroplasia.

The work aimed to evaluate the effectiveness of the developed distraction system based on the rod external monolateral fixation mechanisms by comparing it with the classical technique of long tubular bones distraction based on the circular multi-axial system. The study included patients with a genetically confirmed diagnosis of achondroplasia. The experimental group consisted of 14 patients who underwent surgical limb lengthening by the rod monolateral external fixator with a distraction system developed by the authors. The lengthening was performed on 28 segments of tubular bones. The majority of the experimental group patients achieved the lengthening value close to the planned one and the deformation correction. The fixation period was averagely 83.8 ± 3.7 days, the regenerate length was 8.5 ± 0.6 cm, and the mechanical strength of the distraction regenerate was 10.3° ± 2.18°. The rod external fixator with a control distraction system developed by the authors has small dimensions and low weight of the external supporting elements of high durability. It is reported to provide a good psychological tolerance of the treatment process and significantly outperforms the circular multi-axis system. Considering the aforementioned, the proposed apparatus can grant good orthopedic care to patients with achondroplasia.

Advantages and Disadvantages of Different Treatment Methods in Achondroplasia: A Review.

Achondroplasia (ACH) is a disease caused by a missense mutation in the FGFR3 (fibroblast growth factor receptor 3) gene, which is the most common cause of short stature in humans. The treatment of ACH is necessary and urgent because untreated achondroplasia has many complications, both orthopedic and neurological, which ultimately lead to disability. This review presents the current and potential pharmacological treatments for achondroplasia, highlighting the advantages and disadvantages of all the drugs that have been demonstrated in human and animal studies in different stages of clinical trials. The article includes the potential impacts of drugs on achondroplasia symptoms other than short stature, including their effects on spinal canal stenosis, the narrowing of the foramen magnum and the proportionality of body structure. Addressing these effects could significantly improve the quality of life of patients, possibly reducing the frequency and necessity of hospitalization and painful surgical procedures, which are currently the only therapeutic options used. The criteria for a good drug for achondroplasia are best met by recombinant human growth hormone at present and will potentially be met by vosoritide in the future, while the rest of the drugs are in the early stages of clinical trials.

Biallelic deep intronic variant c.5457+81T>A in TRIP11 causes loss of function and results in achondrogenesis 1A.

Biallelic loss of function variants in TRIP11 encoding for the Golgi microtubule-associated protein 210 (GMAP-210) causes the lethal chondrodysplasia achondrogenesis type 1A (ACG1A). Loss of TRIP11 activity has been shown to impair Golgi structure, vesicular transport, and results in loss of IFT20 anchorage to the Golgi that is vital for ciliary trafficking and ciliogenesis. Here, we report four fetuses, two each from two families, who were ascertained antenatally with ACG1A. Affected fetuses in both families are homozygous for the deep intronic TRIP11 variant, c.5457+81T>A, which was found in a shared region of homozygosity. This variant was found to cause aberrant transcript splicing and the retention of 77 base pairs of intron 18. The TRIP11 messenger RNA and protein levels were drastically reduced in fibroblast cells derived from one of the affected fetuses. Using immunofluorescence we also detected highly compacted Golgi apparatus in affected fibroblasts. Further, we observed a significant reduction in the frequency of ciliated cells and in the length of primary cilia in subject-derived cell lines, not reported so far in patient cells with TRIP11 null or hypomorphic variants. Our findings illustrate how pathogenic variants in intronic regions of TRIP11 can impact transcript splicing, expression, and activity, resulting in ACG1A.

Childhood prevalence of achondroplasia in New South Wales and the Australian Capital Territory, Australia.

The aim of this study was to estimate the childhood prevalence of achondroplasia, trends over time in birth prevalence, and age at diagnosis in Australia. Children born between 1990 and 2019 with a clinical and radiological and/or molecular diagnosis of achondroplasia were identified from a tertiary hospital servicing New South Wales (NSW) and the Australian Capital Territory (ACT) and compared with population data from the Australian Bureau of Statistics. Childhood prevalence of achondroplasia, based on children ≤19 years of age and resident in NSW/ACT on June 30, 2019 (n = 109), was 5.2 per 100,000. A total of 127 individuals with achondroplasia were born in 1990-2019 in NSW/ACT. Birth prevalence rates increased across birth decades, from 3.3 per 100,000 live births in 1990-1999 to 5.3 per 100,000 in 2010-2019 (p < 0.0001). Median age at diagnosis decreased to 17 days in 2010-2019 compared with 30 days in 1990-1999 (p = 0.035), although the overall decreasing trend across consecutive decades did not reach statistical significance. This is the first study to show a rising birth prevalence rate for achondroplasia in Australia with a concurrent decreasing age at diagnosis, both of which were statistically significant after 2 decades.

CLARITY: Co-occurrences in achondroplasia-craniosynostosis, seizures, and decreased risk of diabetes mellitus.

Achondroplasia is the most common disproportionate short statured skeletal dysplasia with a prevalence of approximately 1:20,000-30,000. We created the largest database to date of a historical cohort of 1374 patients with achondroplasia (CLARITY-aChondropLasia nAtuRal hIsTory studY). This cohort was queried for the presence of unrecognized or under-recognized features associated with achondroplasia. Craniosynostosis was found to co-occur with achondroplasia in 9 (0.65%) patients in this cohort, which is much higher than the general population prevalence of 3.1-7.2 per 10,000. In addition, 27 patients had seizures (2.0%), an apparent excess as compared to the general population. Only two people had diabetes despite a high rate of adult obesity. This report documents for the first time an increased prevalence of craniosynostosis in persons with achondroplasia, and adds support to previous observations of an apparently higher than expected prevalence of seizures and lower prevalence of diabetes mellitus.

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.

Typical achondroplasia secondary to a unique insertional variant of FGFR3 with in vitro demonstration of its effect on FGFR3 function.

We describe an individual in whom clinical and radiographic features are typical for achondroplasia, but in whom the common variants of FGFR3 that result in achondroplasia are absent. Whole exome sequencing demonstrated a novel, de novo 6 base pair tandem duplication in FGFR3 that results in the insertion of Ser-Phe after position Leu324. in vitro studies showed that this variant results in aberrant dimerization, excessive spontaneous phosphorylation of FGFR3 dimers and excessive, ligand-independent tyrosine kinase activity. Together, these data suggest that this variant leads to constitutive disulfide bond-mediated dimerization, and that this, surprisingly, occurs to an extent similar to the neonatal lethal thanatophoric dysplasia type I Ser249Cys variant.

Birth prevalence of achondroplasia: A systematic literature review and meta-analysis.

Achondroplasia is a genetic disorder that results in disproportionate short stature. The true prevalence of achondroplasia is unknown as estimates vary widely. This systematic literature review and meta-analysis was conducted to better estimate worldwide achondroplasia birth prevalence. PubMed, Embase, Scielo, and Google Scholar were searched, complemented by manual searching, for peer-reviewed articles published between 1950 and 2019. Eligible articles were identified by two independent researchers using predefined selection criteria. Birth prevalence estimates were extracted for analysis, and the quality of evidence was assessed. A meta-analysis using a quality effects approach based on the inverse variance fixed effect model was conducted. The search identified 955 unique articles, of which 52 were eligible and included. Based on the meta-analysis, the worldwide birth prevalence of achondroplasia was estimated to be 4.6 per 100,000. Substantial regional variation was observed with a considerably higher birth prevalence reported in North Africa and the Middle East compared to other regions, particularly Europe and the Americas. Higher birth prevalence was also reported in specialized care settings. Significant heterogeneity (Higgins I2 of 84.3) was present and some indication of publication bias was detected, based on visual asymmetry of the Doi plot with a Furuya-Kanamori index of 2.73. Analysis of pooled data from the current literature yields a worldwide achondroplasia birth prevalence of approximately 4.6 per 100,000, with considerable regional variation. Careful interpretation of these findings is advised as included studies are of broadly varying methodological quality.

Mutant COMP shapes growth and development of skull and facial structures in mice and humans.

BACKGROUND: Cartilage oligomeric matrix protein (COMP) is an important extracellular matrix protein primarily functioning in the musculoskeletal tissues and especially endochondral bone growth. Mutations in COMP cause the skeletal dysplasia pseudoachondroplasia (PSACH) that is characterized by short limbs and fingers, joint laxity, and abnormalities but a striking lack of skull and facial abnormalities. METHODS: This study examined both mice and humans to determine how mutant-COMP affects face and skull growth. RESULTS: Mutant COMP (MT-COMP) mice were phenotypically distinct. Snout length and skull height were diminished in MT-COMP mouse and the face more closely resembled younger controls. Three-dimensional facial measurements of PSACH faces showed widely spaced eyes, reduced lower facial height, and decreased nasal protrusion, which correlated with a more juvenile appearing face. Neither MT-COMP mice nor PSACH individuals show midface hypoplasia usually associated with abnormal endochondral bone growth. MT-COMP mice do show delayed endochondral and membranous skull ossification that normalizes with age. CONCLUSION: Therefore, mutant-COMP affects both endochondral and intramembranous bones of the skull resulting in a reduction of the nose and lower facial height in mice and humans, in addition to its well-defined role in the growth plate chondrocytes.

Pharmacokinetics and safety after once and twice a day doses of meclizine hydrochloride administered to children with achondroplasia.

Achondroplasia (ACH) is the most common short-limbed skeletal dysplasia caused by activating mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. We identified that meclizine hydrochloride inhibited FGFR3 signaling in various chondrocytic cells and promoted longitudinal bone growth in mouse model of ACH. Meclizine has safely been used for more than 50 years, but it lacks the safety data for repeated administration and pharmacokinetics (PK) when administered to children. We performed a phase Ia study to evaluate the PK and safety of meclizine administered orally to ACH children. Twelve ACH children aged from 5 to younger than 11 years were recruited, and the first 6 subjects received once a day of meclizine in the fasted condition, subsequent 6 subjects received twice a day of meclizine in the fed condition. Meclizine was well tolerated in ACH children with no serious adverse events. The mean Cmax, Tmax, AUC0-24h, t1/2 during 24 hours in the fasted condition were 130 ng/mL, 1.7 hours, 761 ng·h/mL, and 8.5 hours respectively. The simulation of repeated administration of meclizine for 14 days demonstrated that plasma concentration apparently reached steady state around 10 days after the first dose both at once a day and twice a day administration. The AUC0-10h of the fasting and fed condition were 504 ng·h/mL and 813 ng·h/mL, respectively, indicating exposure of meclizine increased with the diet. Although higher drug exposure was confirmed in ACH children compared to adults, a single administration of meclizine seemed to be well tolerated.

Lumbar spinal stenosis and disc alterations affect the upper lumbar spine in adults with achondroplasia.

In achondroplasia, lumbar spinal stenosis arises from congenital dysplasia and acquired degenerative changes. We here aimed to describe the changes of the lumbar spinal canal and intervertebral disc in adults. We included 18 adults (age ≥ 18 years) with achondroplasia and lumbar spinal stenosis. Radiographs were used to analyze spinal-pelvic angles. Antero-posterior diameter of the spinal canal and the grade of disc degeneration were measured by MRI. Antero-posterior diameters of the spinal canal differed by spinal level (P < 0.05), with lower values observed at T12-L1, L1-2 and L2-3. Degrees of disc degeneration differed by intervertebral level, with higher degrees observed at L1-2, L2-3 and L3-4. A significant correlation was found between disc degeneration and thoraco-lumbar kyphosis at L2-3, between antero-posterior diameter of the spinal canal and lumbar lordosis at T12-L1 and L2-3, and between antero-posterior diameter of the spinal canal and thoraco-lumbar kyphosis at L1-2. Unlike the general population, spinal stenosis and disc degeneration involve the upper part of the lumbar spine in adults with achondroplasia, associated with thoraco-lumbar kyphosis and loss of lumbar lordosis.

Severe achondroplasia due to two de novo variants in the transmembrane domain of FGFR3 on the same allele: A case report.

BACKGROUND: Achondroplasia (ACH), the most common form of short-limbed skeletal dysplasia, is caused by gain-of-function mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. More than 97% of patients result from a heterozygous p.G380R mutation in the FGFR3 gene. We present here a child who had two de novo variants in the FGFR3 on the same allele, a common p.G380R mutation and a novel p.S378N variant. METHODS: A 3-year-old Japanese girl born from non-consanguineous healthy parents showed more severe clinical and radiological phenotypes than classic ACH, including severe short-limbed short stature with marked ossification defects in the metaphysis and epiphysis, hydrocephalus and cervicomedullary compression due to foramen magnum stenosis, prolonged pulmonary hypoplasia, and significant delay in the gross motor development. Genomic DNA was extracted from the proband and whole-exome sequencing was performed. The variants were subsequently confirmed by Sanger sequencing. RESULTS: Mutation analysis demonstrated that the proband had p.S378N (c.1133G>A) and p.G380R (c.1138G>A) variants in the FGFR3 gene. Both variants were not detected in her parents and therefore considered de novo. An allele-specific PCR was developed in order to determine whether these mutations were on the same allele (cis) or on different alleles (trans). The c.1138G>A mutation was found in the PCR product generated with the primer for the mutant 1133A, but it was not detected in the product with the wild-type 1133G, confirming that p.S378N and p.G380R variants were located on the same allele (cis). CONCLUSION: This is the second case who had two FGFR3 variants in the transmembrane domain on the same allele. The p.S378N variant may provide an additive effect on the activating receptor with the p.G380R mutation and alter the protein function, which could be responsible for the severe phenotype of the present case.