Genotype phenotype correlation in achondroplasia and hypochondroplasia

Radiological characteristics of skeletal growth in neonates and infants with achondroplasia

Achondroplasia (ACH) is the most common form of skeletal dysplasia characterized by a rhizomelic short stature. Radiological skeletal findings in pediatric and adult patients with ACH include short long bones, a relatively longer fibula compared to the tibia, a narrow lumbar interpedicular distance, and a hypoplastic iliac wing. Nonetheless, the characteristics of skeletal growth during the neonatal and infantile periods have scarcely been explored. Therefore, this retrospective study aimed to analyze the radiological skeletal growth during the neonatal and infantile periods in 41 Japanese patients with genetically confirmed ACH. The length of long bones in the upper and lower limbs and the lumbar interpedicular distances at L1 and L4 were measured. These parameters showed significant positive correlations with age. The upper segment-to-lower segment ratio in the lower limbs resembled the data of healthy controls from previous reports. The L1/L4 and fibula/tibia ratios increased with age, suggesting that some representative skeletal phenotypes of ACH were less distinct during the neonatal and infantile periods. In conclusion, for the first time, this study radiologically characterized skeletal growth during the neonatal and infantile periods of patients with genetically confirmed ACH.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Molecular therapeutic strategies for FGFR3 gene-related skeletal dysplasia

The FGFR3 gene encodes fibroblast growth factor receptor 3 protein, a negative regulator of chondrogenesis. Gain-of-function mutations result in constitutively activated FGFR3, leading to aberrant signal transduction, and accounting for inhibition of chondrocyte proliferation and differentiation. Generally, these pathogenic mutations maintain FGFR3 in an active state and cause diverse phenotypes in patients with skeletal dysplasia. For decades, studies have revealed the molecular mechanisms of constitutively activated FGFR3 and relevant therapeutic strategies. By modulating the FGFR3-induced signalling pathway with methods such as blocking binding between ligands and receptors, blocking tyrosine kinase activities, or antagonising the FGFR3 downstream signalling pathway, these strategies offer the possibility to ameliorate FGFR3 gene-related skeletal dysplasia phenotypes. In this review, we describe the mechanisms of potential therapeutic targets and underlying regulators and then systematically review molecular therapeutic strategies for FGFR3 gene-related skeletal dysplasia based on current knowledge.

Identification and in silico characterization of p.G380R substitution in FGFR3, associated with achondroplasia in a non-consanguineous Pakistani family

Background

The dimerization efficiency of FGFR3 transmembrane domain plays a critical role in the formation of a normal skeleton through the negative regulation of bone development. Recently, gain-of-function mutations in the transmembrane domain of FGFR3 has been described associated with an aberrant negative regulation, leading to the development of achondroplasia-group disorders, including achondroplasia (ACH), hypochondroplasia (HCH) and thanatophoric dysplasia (TD). Here, we describe a non-consanguineous Pakistani family with achondroplasia to explain hereditary basis of the disease.

Methods

PCR-based linkage analysis using microsatellite markers was employed to localize the disease gene. Gene specific intronic primers were used to amplify the genomic DNA from all affected as well as phenotypically healthy individuals. Amplified PCR products were then subjected to Sanger sequencing and RFLP analysis to identify a potentially pathogenic mutation. The impact of identified mutation on FGFR3 protein’s structure and stability was highlighted through different bioinformatics tools.

Results

Genetic screening of the family revealed a previously reported heterozygous c.1138 G > A (p.G380R) mutation in the coding exon 8 of FGFR3 gene. Identified genetic variation was confirmed in all affected individuals while healthy individuals and controls were found genotypically normal. The results were further validated by RFLP analysis as c.1138 G > A substitution generates a unique recognition site for SfcI endonuclease. Following SfcI digestion, the electrophoretic pattern of three bands/DNA fragments for each patient is indicative of heterozygous status of the disease allele. In silico studies of the mutant FGFR3 protein predicted to adversely affect the stability of FGFR3 protein.

Conclusions

Mutation in the transmembrane domain may adversely affect the dimerization efficiency and overall stability of the FGFR3, leading to a constitutively active protein. As a result, an uncontrolled intracellular signaling or negative bone growth regulation leads to achondroplasia. Our findings support the fact that p.G380R is a common mutation among diverse population of the world and like other countries, can be used as a molecular diagnosis marker for achondroplasia in Pakistan.

Electronic supplementary material

The online version of this article (doi:10.1186/s13000-017-0642-3) contains supplementary material, which is available to authorized users.

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.

Concomitant achondroplasia and developmental dysplasia of the hip

Achondroplasia (ACH) is the most common form of hereditary dwarfism and presents with multiple musculoskeletal anomalies but is not normally associated with premature hip arthritis. Developmental dysplasia of the hip (DDH) is a spectrum of disease resulting in shallow acetabular depth and a propensity for chronic femoral subluxation or dislocation; it is among the most common causes of premature arthritis. This case report describes the diagnosis of symptomatic DDH in a patient with ACH and highlights difficulties of primary total hip arthroplasty (THA) as a treatment option. Intraoperative radiographic imaging is advised to ensure proper prosthesis placement. Femoral osteotomy may aid visualization, reduction, and avoidance of soft tissue injury. Concomitant ACH and DDH is a challenging problem that can be successfully treated with modified THA.

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.

The Fibroblast Growth Factor signaling pathway

The signaling component of the mammalian Fibroblast Growth Factor (FGF) family is comprised of eighteen secreted proteins that interact with four signaling tyrosine kinase FGF receptors (FGFRs). Interaction of FGF ligands with their signaling receptors is regulated by protein or proteoglycan cofactors and by extracellular binding proteins. Activated FGFRs phosphorylate specific tyrosine residues that mediate interaction with cytosolic adaptor proteins and the RAS-MAPK, PI3K-AKT, PLCγ, and STAT intracellular signaling pathways. Four structurally related intracellular non-signaling FGFs interact with and regulate the family of voltage gated sodium channels. Members of the FGF family function in the earliest stages of embryonic development and during organogenesis to maintain progenitor cells and mediate their growth, differentiation, survival, and patterning. FGFs also have roles in adult tissues where they mediate metabolic functions, tissue repair, and regeneration, often by reactivating developmental signaling pathways. Consistent with the presence of FGFs in almost all tissues and organs, aberrant activity of the pathway is associated with developmental defects that disrupt organogenesis, impair the response to injury, and result in metabolic disorders, and cancer. For further resources related to this article, please visit the WIREs website.

Fibroblast growth factor (FGF) signaling in development and skeletal diseases

Fibroblast growth factors (FGF) and their receptors serve many functions in both the developing and adult organism. Humans contain 18 FGF ligands and four FGF receptors (FGFR). FGF ligands are polypeptide growth factors that regulate several developmental processes including cellular proliferation, differentiation, and migration, morphogenesis, and patterning. FGF-FGFR signaling is also critical to the developing axial and craniofacial skeleton. In particular, the signaling cascade has been implicated in intramembranous ossification of cranial bones as well as cranial suture homeostasis. In the adult, FGFs and FGFRs are crucial for tissue repair. FGF signaling generally follows one of three transduction pathways: RAS/MAP kinase, PI3/AKT, or PLCγ. Each pathway likely regulates specific cellular behaviors. Inappropriate expression of FGF and improper activation of FGFRs are associated with various pathologic conditions, unregulated cell growth, and tumorigenesis. Additionally, aberrant signaling has been implicated in many skeletal abnormalities including achondroplasia and craniosynostosis. The biology and mechanisms of the FGF family have been the subject of significant research over the past 30 years. Recently, work has focused on the therapeutic targeting and potential of FGF ligands and their associated receptors. The majority of FGF-related therapy is aimed at age-related disorders. Increased understanding of FGF signaling and biology may reveal additional therapeutic roles, both in utero and postnatally. This review discusses the role of FGF signaling in general physiologic and pathologic embryogenesis and further explores it within the context of skeletal development.

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.

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.

Education and related support from medical specialists for Japanese patients with major skeletal dysplasias

BACKGROUND

Skeletal dysplasias manifest various clinical symptoms. Age at onset, severity, and progression of symptoms differ even among individuals with the same diagnosis. Though necessary support in education is presumed to differ among patients with different disorders, few articles report on education in patients with skeletal dysplasias.

OBJECTIVE

To clarify what types of schools children with major skeletal dysplasias attend, what kind of support they needed at schools, and how the advice on such support was conveyed from medical specialists to schools.

METHODS

Questionnaire study on patients with achondroplasia or hypochondroplasia (A/HCH), and osteogenesis imperfecta (OI).

RESULTS

In A/HCH childhood locomotion ability was high and most patients had received general education, irrespective of their generation. Children with OI showed a lower level of locomotion ability; only about half of them had received general education. In selecting schools, the patients received advice from pediatricians, physiatrists, and orthopedic surgeons. The degree of necessity and content of support at the schools differed between A/HCH and OI. Remodeling of the lavatory, washbasin, and chair and support during swimming lessons were common in A/HCH patients. Support in school for OI patients was more frequent and included propelling wheelchairs, assisting in the use of the bathroom, and remodeling the lavatory. Most children were restricted from participating in physical education classes.

CONCLUSIONS

Locomotion ability and the necessary support at school differed between A/HCH and OI. Support and advice from medical specialists who recognize disability of patients with skeletal dysplasias may improve patients' participation and education in schools.

A novel missense mutation of FGFR3 in a Chinese female and her fetus with Hypochondroplasia by next-generation sequencing

BACKGROUND

Hypochondroplasia (HCH) is a mild, autosomal dominant human skeletal dysplasias characterized by short extremities, short stature and lumbar lordosis. There are three other kinds of dwarfism (Pseudoachondroplasia, Achondroplasia and Thanatophoric Syndromes) with similar clinical features, which makes it difficult to give a precise diagnosis. Molecular genetic analysis of related genes should be employed.

METHODS

In this study, we reported a Chinese family diagnosed as a type of skeletal dysplasia based on clinical and radiologic findings. To make an accurate diagnosis quickly and economically, we performed microarray-based next-generation sequencing (NGS) to detect the variants in the disease-related genes (FGFR3 and COMP).

RESULTS

The mother presents short limbed stature, short iliac bones, short femoral necks, short stubby tibia and mildly increased fibular length and genu varum. Her fetus demonstrated abnormally short femur at 23 and 28week's gestation by ultrasound scan, and was highly suspected with dwarfism. Eventually, a novel missense mutation (c.1024G>T) in FGFR3 was identified by next-generation sequencing. The substitution is found in both the mother and her fetus. The mutation was further confirmed by Sanger sequencing.

CONCLUSIONS

This is the first report of missense mutation identified in the IgIII domain of the FGFR3 gene using NGS. Our results extended the mutational spectrum of FGFR3 and proved that applications of NGS and bioinformatics are effective methods for skeletal dysplasia diagnosis in clinical practices.

Genetic architecture of body size in mammals

Much of the heritability for human stature is caused by mutations of small-to-medium effect. This is because detrimental pleiotropy restricts large-effect mutations to very low frequencies.

Genetic architecture of body size in mammals

Much of the heritability for human stature is caused by mutations of small-to-medium effect. This is because detrimental pleiotropy restricts large-effect mutations to very low frequencies.

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.

New proposed clinico-radiologic and molecular criteria in hypochondroplasia: FGFR 3 gene mutations are not the only cause of hypochondroplasia

We applied a comprehensive set of clinical and radiological criteria for the diagnosis of hypochondroplasia (HCH) in 160 patients with short stature 58 of whom were diagnosed to have HCH. Taking into account the genotypic and phenotypic variations in HCH, we conducted a study with these 58 patients and tested them for mutations in the fibroblast growth factor receptor 3 (FGFR3) and the short stature homeobox (SHOX) gene. We characterized the phenotypes by clinical and radiologic findings. In the patients with HCH, 19 were included in Group I (FGFR3 mutations-mutations of definite significance), and 39 were in Group II (6 SHOX mutations and 33 negative for disease-causing FGFR3 mutations). The clinical findings were similar in two groups regardless of the presence or absence of mutations. More than 95% of the patients had mesomelic proportions. In Group I, the radiological findings of mesomelia of upper and lower limbs and, L1/L4 ratio in anterior-posterior and lateral view were more typical than in Group II. This study proposes comprehensive clinico-radiological criteria for the diagnosis of HCH, which would help in detecting the true incidence of this underdiagnosed condition. The presence of SHOX mutations suggest genotypic-phenotypic overlap between HCH and Leri-Weill dyschondrosteosis, though further investigation is needed to effectively elucidate the importance of these mutations. Also, the 56.9% of HCH patients with negative mutations for FGFR3 suggests that there are other undiscovered gene mutations associated with this phenotypic entity.

Comparison of clinical, radiological and molecular findings in Korean infants and children with achondroplasia and hypochondroplasia

Achondroplasia (ACH) and hypochondroplasia (HCH) share clinical features characterized by disproportionate short stature with rhizomelic shortening of the limbs. In an attempt to clarify genotype-phenotype correlation in ACH and HCH, we investigated the presence of the previously identified mutations of FGFR3 in 26 patients with ACH- or HCH-mimicking features and compared clinical and radiographic findings between the two groups. Using genomic DNA sequencing and RFLP analysis, G380R, an ACH-specific mutation, and N540K, an HCH-specific mutation, were detected in 13 patients (50%) and five patients (19%), respectively. No mutations of FGFR3 were detected in eight patients (31%). No remarkable clinical or radiological differences were evident among the ACH infants and children with G380R, the HCH patients with N540K, and the patients without verified mutations. These results suggest that genotype-based diagnosis needs to precede proper genetic counseling for patients with ACH or HCH, which show very similar clinical and radiological features.

Retinoblastoma and hypochondroplasia: a case report of two germline mutations arising simultaneously

PURPOSE

To report a rare case of a patient with two germline mutations arising de novo resulting in bilateral retinoblastoma and hypochondroplasia.

DESIGN

A brief review about retinoblastoma and hypochondroplasia; a case report with genetic mutational analysis results.

CASE REPORT

We report a patient manifesting the clinical features of both bilateral retinoblastoma and hypochondroplasia. Genetic analysis revealed two germline mutations, a seven base-pair deletion in exon 12 (G70313-703129del) in one allele of the retinoblastoma gene (RB1) and the N540K (C1620C > A) mutation in one allele of the fibroblast growth factor 3 (FGFR3) gene, a frequent mutation in hypochondroplasia. Neither parent has a personal or family history of cancer or ocular tumors. Only the patient's mother is short in stature, and her genetic analysis revealed no FGFR3 mutations.

CONCLUSIONS

Although the probability of both germline mutations occurring in a single individual is exceedingly low, the etiology and mechanism are unknown in this patient. To the best of our knowledge, this is the first report of two clinically distinct heritable germline mutations arising de novo in an individual.

Skeletal development of achondroplasia: analysis of genotyped patients

BACKGROUND

Achondroplasia is a skeletal dysplasia caused by substitution of arginine for glycine at codon 380 (G380R) mutation of the fibroblast growth factor receptor 3. To date, the developmental course of the phenotype (short stature and skeletal characteristics) has not been clarified in the genotyped population.

METHODS

The relationship between age and clinical data (height, arm span and measurements of skeletal radiographs) were statistically analyzed from 27 achondroplasia patients with the G380R genotype.

RESULTS

The height standard deviation score had positive correlation and decreased with age, while span-to-height ratio did not. Among measurements of skeletal radiographs, the pelvic index, which represents the squared pelvis deformity, were correlated and increased with age. However, interpedicular distance of the first and fourth lumbar vertebrae (L1:L4) ratio as an index for the caudally narrowed pattern of the lumbar spinal canal and fibula-to-tibia ratio for the disproportionally long fibulae were not correlated and did not increase with age.

CONCLUSION

In making a clinical diagnosis of achondroplasia in early infancy, it should be noted that short stature and squared pelvis deformity are not prominent.

Distinct missense mutations of the FGFR3 lys650 codon modulate receptor kinase activation and the severity of the skeletal dysplasia phenotype

The fibroblast growth factor-receptor 3 (FGFR3) Lys650 codon is located within a critical region of the tyrosine kinase-domain activation loop. Two missense mutations in this codon are known to result in strong constitutive activation of the FGFR3 tyrosine kinase and cause three different skeletal dysplasia syndromes-thanatophoric dysplasia type II (TD2) (A1948G [Lys650Glu]) and SADDAN (severe achondroplasia with developmental delay and acanthosis nigricans) syndrome and thanatophoric dysplasia type I (TD1) (both due to A1949T [Lys650Met]). Other mutations within the FGFR3 tyrosine kinase domain (e.g., C1620A or C1620G [both resulting in Asn540Lys]) are known to cause hypochondroplasia, a relatively common but milder skeletal dysplasia. In 90 individuals with suspected clinical diagnoses of hypochondroplasia who do not have Asn540Lys mutations, we screened for mutations, in FGFR3 exon 15, that would disrupt a unique BbsI restriction site that includes the Lys650 codon. We report here the discovery of three novel mutations (G1950T and G1950C [both resulting in Lys650Asn] and A1948C [Lys650Gln]) occurring in six individuals from five families. Several physical and radiological features of these individuals were significantly milder than those in individuals with the Asn540Lys mutations. The Lys650Asn/Gln mutations result in constitutive activation of the FGFR3 tyrosine kinase but to a lesser degree than that observed with the Lys540Glu and Lys650Met mutations. These results demonstrate that different amino acid substitutions at the FGFR3 Lys650 codon can result in several different skeletal dysplasia phenotypes.

Hereditary disorders mimicking and/or causing premature osteoarthritis

Osteoarthritis is the most common joint disease, causing considerable disability and impairment of quality of life. Hereditary osteochondrodysplasias and some inborn errors of metabolism may mimic or cause premature osteoarthritis. Osteochondrodysplasias usually cause joint deformities, such as coxa vara or genu varum, which can cause abnormal biomechanics. In most of these disorders, the articular cartilage is originally defective as a result of genetically determined collagen or matrix protein abnormalities, or the deposition of mucopolysaccharides. In the case of inborn errors of metabolism, the pathological process affects healthy articular structures, causing secondary osteoarthritis. In alkaptonuria, the pathological deposition of polymerized homogenistic acid causes defective changes in cartilage, articular capsule and tendons. In Wilson's disease, the premature osteoarthritis might be caused by the copper deposition. It is worth paying attention to these rare disorders, even when they are mild or incomplete, because early diagnosis can lead to prevention and effective treatment. In addition, research is discovering the specific gene defects and molecular abnormalities that are responsible for disease expression. This may in turn lead to opportunities for prenatal diagnosis; thus, genetic counselling and gene replacement therapy may be a realistic possibility in the near future.