Spondylo-epi-metaphyseal dysplasia

Clinical, genetic and structural delineation of RPL13-related spondyloepimetaphyseal dysplasia suggest extra-ribosomal functions of eL13

Spondyloepimetaphyseal dysplasia with severe short stature, RPL13-related (SEMD-RPL13), MIM#618728), is a rare autosomal dominant disorder characterized by short stature and skeletal changes such as mild spondylar and epimetaphyseal dysplasia affecting primarily the lower limbs. The genetic cause was first reported in 2019 by Le Caignec et al., and six disease-causing variants in the gene coding for a ribosomal protein, RPL13 (NM_000977.3) have been identified to date. This study presents clinical and radiographic data from 12 affected individuals aged 2-64 years from seven unrelated families, showing highly variable manifestations. The affected individuals showed a range from mild to severe short stature, retaining the same radiographic pattern of spondylar- and epi-metaphyseal dysplasia, but with varying severity of the hip and knee deformities. Two new missense variants, c.548 G>A, p.(Arg183His) and c.569 G>T, p.(Arg190Leu), and a previously known splice variant c.477+1G>A were identified, confirming mutational clustering in a highly specific RNA binding motif. Structural analysis and interpretation of the variants' impact on the protein suggests that disruption of extra-ribosomal functions of the protein through binding of mRNA may play a role in the skeletal phenotype of SEMD-RPL13. In addition, we present gonadal and somatic mosaicism for the condition.

Genetics of skeletal proportions in two different populations

Human height can be divided into sitting height and leg length, reflecting growth of different parts of the skeleton whose relative proportions are captured by the ratio of sitting to total height (as sitting height ratio, SHR). Height is a highly heritable trait, and its genetic basis has been well-studied. However, the genetic determinants of skeletal proportion are much less well-characterized. Expanding substantially on past work, we performed a genome-wide association study (GWAS) of SHR in ∼450,000 individuals with European ancestry and ∼100,000 individuals with East Asian ancestry from the UK and China Kadoorie Biobanks. We identified 565 loci independently associated with SHR, including all genomic regions implicated in prior GWAS in these ancestries. While SHR loci largely overlap height-associated loci (P < 0.001), the fine-mapped SHR signals were often distinct from height. We additionally used fine-mapped signals to identify 36 credible sets with heterogeneous effects across ancestries. Lastly, we used SHR, sitting height, and leg length to identify genetic variation acting on specific body regions rather than on overall human height.

A pictorial review of the radiographic skeletal findings in Morquio syndrome (mucopolysaccharidosis type IV)

Morquio syndrome, also known as Morquio-Brailsford syndrome or mucopolysaccharidosis type IV (MPS IV), is a subgroup of mucopolysaccharidosis. It is an autosomal recessive lysosomal storage disorder. Two subtypes of Morquio syndrome have been identified. In MPS IVA, a deficiency in N-acetylgalactosamine-6-sulfate sulfatase interrupts the normal metabolic pathway of degrading glycosaminoglycans. Accumulated undigested glycosaminoglycans in the tissue and bones result in complications leading to severe skeletal deformity. In MPS IVB, a deficiency in beta-galactosidase results in a milder phenotype than in MPS IVA. Morquio syndrome presents a variety of clinical manifestations in a spectrum of mild to severe. It classically has been considered a skeletal dysplasia with significant skeletal involvement. However, the extraskeletal features can also provide valuable information to guide further work-up to assess the possibility of the disorder. Although the disease involves almost all parts of the body, it most commonly affects the axial skeleton, specifically the vertebrae. The characteristic radiologic findings in MPS IV, such as paddle-shaped ribs, odontoid hypoplasia, vertebral deformity, metaphyseal and epiphyseal bone dysplasia, and steep acetabula, are encompassed in the term "dysostosis multiplex," which is a common feature among other types of MPS and storage disorders. Myelopathy due to spinal cord compression and respiratory airway obstruction are the most critical complications related to mortality and morbidity. The variety of clinical features, as well as overlapping of radiological findings with other disorders, make diagnosis challenging, and delays in diagnosis and treatment may lead to critical complications. Timely imaging and radiologic expertise are important components for diagnosis. Gene therapies may provide robust treatment, particularly if genetic variations can be screened in utero.

Exploring and expanding the phenotype and genotype diversity in seven Chinese families with spondylo-epi-metaphyseal dysplasia

Spondylo-epi-metaphyseal dysplasia (SEMD) is a heterogeneous group of disorders with different modes of inheritance and is characterized by disproportionate or proportionate short stature. To date, more than 30 disease-causing genes have been identified, and different types of SEMD exhibit greatly overlapping clinical features, which usually complicate the diagnosis. This study was performed to expand the clinical and molecular spectrum of SEMD among Chinese subjects and to explore their potential phenotype–genotype relations. We enrolled seven families including 11 affected patients with SEMD, and their clinical, radiographic, and genetic data were carefully analyzed. All the seven probands showed different degrees of short stature, and each of them exhibited additional specific skeletal manifestations; four probands had extraosseous manifestations. X-rays of the seven probands showed common features of SEMD, including vertebral deformities, irregular shape of the epiphysis, and disorganization of the metaphysis. Seven variants were identified in TRPV4 (c.694C&gt; T, p.Arg232Cys), COL2A1 (c.654 + 1G &gt; C; c.3266_3268del, p.Gly1089del), CCN6 (c.396 T&gt; G, p.Cys132Trp; c.721 T&gt;C, p.Cys241Arg), SBDS (c.258 + 2T&gt; C), and ACAN (c.1508C&gt; A, p.Thr503Lys) genes, and two of them were novel. Two families with TRPV4 variants showed considerable intrafamily and interfamily heterogeneities. In addition, we reported one case of SEMD with a severe phenotype caused by ACAN gene mutation. Our study expands the phenotype and genetic spectrum of SEMD and provides evidence for the phenotype–genotype relations, aiding future molecular and clinical diagnosis as well as procreative management of SEMD.

DDRGK1 is required for the proper development and maintenance of the growth plate cartilage

Loss-of-function mutations in DDRGK1 have been shown to cause Shohat type spondyloepimetaphyseal dysplasia (SEMD). In zebrafish, loss of function of ddrgk1 leads to defects in early cartilage development. Ddrgk1-/- mice show delayed mesenchymal condensation in the limb buds and early embryonic lethality. Mechanistically, Ddrgk1 interacts with Sox9 and reduces ubiquitin-mediated proteasomal degradation of Sox9 protein. To investigate the cartilage-specific role of DDRGK1, conditional knockout mice were generated by intercrossing Prx1-Cre transgenic mice with Ddrgkfl/fl mice to delete its expression in limb mesenchymal cells. Mutant mice showed progressive severe shortening of the limbs and joint abnormalities. The growth plate showed disorganization with shortened proliferative zone and enlarged hypertrophic zone. In correlation with these findings, Sox9 and Col2a1 protein levels were decreased, while Col10a1 expression was expanded. These data demonstrate the importance of Ddrgk1 during growth plate development. In contrast, deletion of Ddrgk1 with the osteoblast-specific Osteocalcin-Cre and Leptin receptor-Cre lines did not show bone phenotypes, suggesting that the effect on limb development is cartilage-specific. To evaluate the role of DDRGK1 in cartilage postnatal homeostasis, inducible Agc1-CreERT2; Ddrgklfl/fl mice were generated. Mice in which Ddrgk1 was deleted at 3 months of age showed disorganized growth plate, with significant reduction in proteoglycan deposition. These data demonstrate a postnatal requirement for Ddrgk1 in maintaining normal growth plate morphology. Together, these findings highlight the physiological role of Ddrgk1 in the development and maintenance of the growth plate cartilage. Furthermore, these genetic mouse models recapitulate the clinical phenotype of short stature and joint abnormalities observed in patients with Shohat type SEMD.

Identification of variants in ACAN and PAPSS2 leading to spondyloepi(meta)physeal dysplasias in four Chinese families

Background

Spondyloepi(meta)physeal dysplasias (SE[M]D) are a group of inherited skeletal disorders that mainly affect bone and cartilage, and next‐generation sequencing has aided the detection of genetic defects of such diseases. In this study, we aimed to identify causative variants in four Chinese families associated with SE(M)D.

Methods

We recruited four unrelated Chinese families all displaying short stature and growth retardation. Clinical manifestations and X‐ray imaging were recorded for all patients. Candidate variants were identified by whole‐exome sequencing (WES) and verified by Sanger sequencing. Pathogenicity was assessed by conservation analysis, 3D protein modeling and in silico prediction, and was confirmed according to American College of Medical Genetics and Genomics.

Results

Three novel SE(M)D‐related variants c.1090dupG, c.7168 T > G, and c.2947G > C in ACAN, and one reported variant c.712C > T in PAPSS2 were identified. Among them, c.1090dupG in ACAN and c.712C > T in PAPSS2 caused truncated protein and the other two variants led to amino acid alterations. Conservation analysis revealed sites of the two missense variants were highly conserved, and bioinformatic findings confirmed their pathogenicity. 3D modeling of mutant protein encoded by c.7168 T > G(p.Trp2390Gly) in ACAN proved the structural alteration in protein level.

Conclusion

Our data suggested ACAN is a common pathogenic gene of SE(M)D. This study enriched the genetic background of skeletal dysplasias, and expanded the mutation spectra of ACAN and PAPSS2.

Expanding the phenotypic spectrum of RPL13-related skeletal dysplasia

RPL13-related disorder is a newly described skeletal dysplasia characterized as a form of spondyloepimetaphyseal dysplasia with normal birth length, early postnatal growth deficiency, severe short stature, and genu varum. We present a 9-year-old male with a history of lower leg pain and concern for an unspecified form of multiple epiphyseal dysplasia (MED). Exome sequencing revealed a de novo heterozygous RPL13 c.477+1G>A (IVS4+1G>A) pathogenic variant. This is the first identified case of an individual with an RPL13-related skeletal dysplasia, normal height, and radiographs consistent with a form of MED and Legg-Calve-Perthes-like disease. This case expands the phenotype of RPL13-related disorders.

UFSP2-related spondyloepimetaphyseal dysplasia: A confirmatory report

Spondyloepimetaphyseal dysplasias (SEMDs), which comprise a heterogeneous group of autosomal-dominant, autosomal-recessive and X-linked recessive disorders, are characterized by anomalies of the spine, the epiphyses and metaphyses of the long bones, resulting in short stature and osteoarthritic changes of the joints. UFSP2 gene encodes a highly conserved cysteine protease which cleaves two C-terminal residues from ubiquitin-fold modifier 1, an ubiquitin-like post-translational modifier protein. In 2018, Di Rocco, M reported for the first time that a novel heterozygous variant exon 11: c.1277A > C of the UFSP2 gene was the cause to spondyloepimetaphyseal dysplasia mainly manifested as: short stature, anterior vertebral dysplasia, hip dysplasia, flat vertebra, spinal metaphyseal dysplasia, irregular acetabular apex, distal femoral metaphyseal dysplasia, proximal tibial metaphyseal dysplasia, osteoarthritis and so on. In this report, we describe a boy with spondyloepimetaphyseal dysplasia due to a novel mutation exon 11: c.1283A > G (leading to p. H428R) of the UFSP2 gene. This is the second report to describe children with SEMDs associated with an UFSP2 variant. However, it is the first to describe a UFSP2 gene mutation exon 11: c.1283A > G (leading to p. H428R). Our findings of a novel heterozygous mutation of UFSP2 gene add to the list of 2 reported heterozygous mutations of UFSP2 which led to hereditary osteopathy.

A novel homozygous missense variant in MATN3 causes spondylo-epimetaphyseal dysplasia Matrilin 3 type in a consanguineous family

Spondylo-epimetaphyseal dysplasia Matrilin 3 type (SEMD) is a rare autosomal recessive skeletal dysplasia characterized by short stature, abnormalities in the vertebral bodies and long bones, especially the lower limbs. We enrolled a consanguineous family from Pakistan in which multiple siblings suffered from severe skeletal dysplasia. The six affected subjects ranged in heights from 100 to 136 cm (~-6 standard deviation). Lower limb abnormalities with variable varus and valgus deformities and joint dysplasia were predominant features of the clinical presentation. Whole exome sequencing (WES) followed by Sanger sequencing identified a missense variant, c.542G > A, p.(Arg181Gln) in MATN3 as the genetic cause of the disorder. The variant was homozygous in all affected individuals while the obligate carriers had normal heights with no skeletal symptoms, consistent with a recessive pattern of inheritance. Multiple sequence alignment revealed that MATN3 domain affected by the variant is highly conserved in orthologous proteins. The c.542G > A, p.(Arg181Gln) variant is only the fourth variant in MATN3 causing an autosomal recessive disorder and thus expands the genotypic spectrum.

Spondylo-epi-metaphyseal dysplasia due to a homozygous missense mutation in the gene encoding Matrilin-3 (T120M)

Introduction

Spondylo-epi-metaphyseal dysplasia (SEMD) represents a group of osteo-chondrodysplasias characterized by vertebral, epiphyseal as well as metaphyseal abnormalities. Several genes have been identified underlying the different forms.

Methodology and results

Two relatives (cousins) in a family were found to have disproportionate short stature with clinical and radiological features suggestive of SEMD. Metabolic bone profile was normal including parathyroid hormone and 25(OH)vitamin D3. Exome sequencing revealed a missense mutation (p. T120M) in the von-Willebrand factor A-domain of the Matrilin 3 (MATN3) gene that segregates with the disease in the family.

Conclusion

We identified a homozygous missense mutation in MATN3, an important structural component of the extracellular matrix of cartilage, as the genetic cause of SEMD in this pedigree. MATN3 mutations have been more commonly associated with multiple epiphyseal dysplasia than SEMD. Recognition of this mutation will aid in enhancing the understanding and expanding the spectrum of this particular skeletal dysplasia.

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SEMD due to Matrilin-3 mutation is rare and needs further characterisation.

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Infantile onset of disproportionate dwarfism and progressive bowing of knees and elbows are diagnostic clues.

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Absence of extraskeletal features is noteworthy.

A Novel Homozygous Frameshift Mutation in CCN6 Causing Progressive Pseudorheumatoid Dysplasia (PPRD) in a Consanguineous Yemeni Family

Background: Progressive pseudorheumatoid dysplasia (PPRD) inherited in an autosomal recessive fashion, is a disabling disease, characterized by platyspondyly, irregularities of the vertebral bodies, narrowing of the intervertebral discs and intraarticular spaces, widening of the epiphysis-metaphysis, polyarthralgia, multiple joint contractures, and disproportionate short stature. A number of studies have been performed on this deformity in various populations around the globe, including the Arab population. Mutations in CCN6, located on 6q22, are reported to cause this anomaly. Case Presentation: The present study describes the investigation of a consanguineous family of Yemeni origin. Clinical examination of the patient revealed short stature with progressive skeletal abnormalities, stiffness and enlargement of small joints of the hands along with restriction of movements of proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints with weakness and gait disturbance. Sanger sequencing revealed a novel homozygous frameshift deletion mutation (c.746delT; p.Val249Glyfs^*10) in CCN6 which may lead to NMD (Nonsense mediated decay). This mutation expands the spectrum of pathogenic variants in CCN6 causing PPRD.

Progressive Pseudorheumatoid Dysplasia Misdiagnosed as Seronegative Juvenile Idiopathic Arthritis

Background

Progressive pseudorheumatoid dysplasia (PPD) is a rare spondylo-epi-metaphyseal dysplasia (SEMD). It can be confused with juvenile idiopathic arthritis (JIA), both clinically and radiologically. Early detection and diagnosis of PPD are important in helping to relieve the pain and disability associated with this disease and in avoiding unnecessary investigations and anti-rheumatic interventions.

Case Details

We report the case of a 15-year-old girl with PPD who was misdiagnosed with JIA.

Conclusion

In conclusion, PPD is a rare SEMD and can be confused with JIA, both clinically and radiologically. Early detection and diagnosis of PPD are important in helping to relieve the pain and disability associated with this disease and in avoiding unnecessary investigations and anti-rheumatic interventions.

Loss of DDRGK1 modulates SOX9 ubiquitination in spondyloepimetaphyseal dysplasia

Shohat-type spondyloepimetaphyseal dysplasia (SEMD) is a skeletal dysplasia that affects cartilage development. Similar skeletal disorders, such as spondyloepiphyseal dysplasias, are linked to mutations in type II collagen (COL2A1), but the causative gene in SEMD is not known. Here, we have performed whole-exome sequencing to identify a recurrent homozygous c.408+1G>A donor splice site loss-of-function mutation in DDRGK domain containing 1 (DDRGK1) in 4 families affected by SEMD. In zebrafish, ddrgk1 deficiency disrupted craniofacial cartilage development and led to decreased levels of the chondrogenic master transcription factor sox9 and its downstream target, col2a1. Overexpression of sox9 rescued the zebrafish chondrogenic and craniofacial phenotype generated by ddrgk1 knockdown, thus identifying DDRGK1 as a regulator of SOX9. Consistent with these results, Ddrgk1-/- mice displayed delayed limb bud chondrogenic condensation, decreased SOX9 protein expression and Col2a1 transcript levels, and increased apoptosis. Furthermore, we determined that DDRGK1 can directly bind to SOX9 to inhibit its ubiquitination and proteasomal degradation. Taken together, these data indicate that loss of DDRGK1 decreases SOX9 expression and causes a human skeletal dysplasia, identifying a mechanism that regulates chondrogenesis via modulation of SOX9 ubiquitination.

Novel DDR2 mutation identified by whole exome sequencing in a Moroccan patient with spondylo-meta-epiphyseal dysplasia, short limb-abnormal calcification type

Spondylo-meta-epiphyseal dysplasia (SMED), short limb-abnormal calcification type (SMED, SL-AC), is a very rare autosomal recessive disorder with various skeletal changes characterized by premature calcification leading to severe disproportionate short stature. Twenty-two patients have been reported until now, but only five mutations (four missense and one splice-site) in the conserved sequence encoding the tyrosine kinase domain of the DDR2 gene has been identified. We report here a novel DDR2 missense mutation, c.370C > T (p.Arg124Trp) in a Moroccan girl with SMED, SL-AC, identified by whole exome sequencing. Our study has expanded the mutational spectrum of this rare disease and it has shown that exome sequencing is a powerful and cost-effective tool for the diagnosis of clinically heterogeneous disorders such as SMED.

Total knee arthroplasty in patients with skeletal dysplasia

INTRODUCTION

Dwarfism is a challenge in arthroplasty. The anatomical features provide a lot of pitfalls. The aim of this study was to follow-up growth-restricted patients after endoprosthetic treatment.

MATERIALS AND METHODS

138 knee arthroplasties in patients with a height ≤150 cm between January 1, 2000 and May 5, 2013 at our institution were enrolled in this study. 124 cases were available for 1-year follow-up. Out of these, 43 cases were available for 5-year follow-up so far. 14 patients were lost to follow-up.

RESULTS

IKS score increased from 35 ± 16 on admission to 67 ± 22 (p < 0.001) at 1-year follow-up and 65 ± 23 (p < 0.001) at 5-year follow-up. Function Score increased from 40 ± 29 on admission to 64 ± 21 (p < 0.001) at 1-year follow-up and 63 ± 23 (p < 0.001) at 5-year follow-up. Revision surgery was required in one case (0.8 %) after 1-year follow-up, and in an additional three cases (7 %) after 5-year follow-up.

CONCLUSIONS

Knee arthroplasty can be performed in patients suffering from dwarfism with good clinical benefits. However, survival rates are worse compared to the general population.

Bilateral rhegmatogenous retinal detachment in spondyloepimetaphyseal dysplasia-Strudwick type

PURPOSE

To document the diagnosis and repair of bilateral retinal detachments in a child with spondyloepimetaphyseal dysplasia-Strudwick type, a rare autosomal dominant genetic disorder involving abnormal production of Type II collagen.

METHODS

Case report.

RESULTS

A 13-year-old patient diagnosed with spondyloepimetaphyseal dysplasia-Strudwick type presented with a localized superior temporal retinal detachment in the right eye and a 180° giant retinal tear with an associated macula-off retinal detachment in the left eye. He was highly myopic and had a visual acuity of 20/80 in the right eye and counting fingers in the left eye. He underwent a pars plana vitrectomy in the left eye and laser retinoplexy in the right eye, achieving complete reattachment and/or stabilization of both retinae, with a visual acuity of 20/60 in the right eye and 20/100 in the left eye at 3 months postoperatively.

CONCLUSION

Patients with spondyloepimetaphyseal dysplasia-Strudwick type may be at a higher risk of developing myopia, vitreoretinal degeneration, and a subsequent retinal detachment, although the scientific literature provides a loose association between these conditions. Critically, we propose a temporal association between retinal detachment and the onset of puberty in these patients and suggest that a dilated retinal screening examination should be scheduled at around the time of puberty for patients with spondyloepimetaphyseal dysplasia-Strudwick type to detect any asymptomatic retinal pathology.

A case of cerebral hypomyelination with spondylo-epi-metaphyseal dysplasia

We reported on a male patient with rare leukoencephalopathy and skeletal abnormalities. The condition was first noticed as a developmental delay, nystagmus and ataxia at 1 year of age. At 4 years of age, he was diagnosed as hypomyelination with skeletal abnormalities from clinical features, brain magnetic resonance imaging (MRI) and skeletal X-rays. His brain MRI revealed diffuse hypomyelination. These findings suggested the classical type of Pelizaeus-Merzbacher disease (PMD) caused by proteolipid protein (PLP)-1 gene or Pelizaeus-Merzbacher-like disease (PMLD). However, we found neither mutation nor duplication of PLP-1. The patient had severe growth retardation and general skeletal dysplasia compatible with spondylo-epi-metaphyseal dysplasia; however the mutation of discoidin domain receptor (DDR) 2 gene was absent. The co-morbidity of hypomyelination with skeletal abnormalities is rare. We performed array CGH and no causal copy number variation was recognized. Alternatively, this condition may have been caused by a mutation of the gene encoding a molecule that functions in both cerebral myelination and skeletal development.

Osteoarthritis year 2012 in review: genetics and genomics

The field of genetics and genomics is a highly technological driven field that is advancing fast. The purpose of this year in review of genetics and genomics was to highlight the publications that apply these new technologies tools to improve understanding of the pathophysiology of osteoarthritis (OA). In addition, most recent developments in genetics and genomics research and their relevance to OA are discussed in this review.

A newly recognized syndrome with characteristic facial features, skeletal dysplasia, and developmental delay

We describe a series of seven male patients from six different families with skeletal dysplasia, characteristic facial features, and developmental delay. Skeletal findings include patellar dislocation, short tubular bones, mild metaphyseal changes, brachymetacarpalia with stub thumbs, short femoral necks, shallow acetabular roofs, and platyspondyly. Facial features include: a flattened midface with broad nasal bridge, cleft palate or bifid uvula and synophrys. All of the patients demonstrated pre-school onset of a cognitive developmental delay with a shortened attention span. Some of the cognitive delay was masked by a warm and engaging personality. We posit that these individuals have a newly recognized syndrome characterized by the described features. There is some phenotypic overlap between these patients and Desbuquois dysplasia; however molecular testing demonstrated that this is a distinct disorder. Given the family information available for each patient, we are suspicious that the constellation of findings reported herein could be an X-linked recessive syndrome.

Spondyloepimetaphyseal dysplasia, short limb-abnormal calcifications type: progressive radiological findings from fetal age to adolescence

BACKGROUND

Spondyloepimetaphyseal dysplasia, short limb-abnormal calcifications type (SEMD, SL-AC) is a rare autosomal recessive condition with a grave prognosis.

OBJECTIVE

We aimed to describe the progression of symptoms from fetal age to adolescence in SMED, SL-AC patients.

MATERIALS AND METHODS

We retrospectively evaluated radiological findings on plain films, CT and MRI for eight children with genetically proven SEMD (male:female ratio 4:4, ages 30-week fetus to 18 years) and summarized findings from case reports and case series in the literature.

RESULTS

Early and persistent radiological signs of SEMD were platyspondyly, chest narrowing, short ribs, and broad and short bones in the extremities and pelvis. In five children, we observed an unusually massive C2 vertebral body with narrowing of the spinal canal. Disease progression was characterized by anterior dislocation of C1, kyphoscoliosis, bowing of the limbs, metaphyseal and epiphyseal changes and abnormal calcifications. Earliest appearance of abnormal calcifications was 1.5 years; four children had no abnormal calcifications at diagnosis. There were persistent large open fontanelles in all children with skull radiographs, including a 17-year-old boy. Disease severity and progression were variable. Complications included cord compression and restrictive lung changes.

CONCLUSION

Disease severity and progression vary. Absence of abnormal calcifications does not preclude the diagnosis. An unusual, massive C2 vertebral body may contribute to spinal cord compression. Persistent open fontanelles should be added to the clinical characteristics of SEMD, SL-AC.

Mutations in DDR2 gene cause SMED with short limbs and abnormal calcifications

The spondylo-meta-epiphyseal dysplasia [SMED] short limb-hand type [SMED-SL] is a rare autosomal-recessive disease, first reported by Borochowitz et al. in 1993.(1) Since then, 14 affected patients have been reported.(2-5) We diagnosed 6 patients from 5 different consanguineous Arab Muslim families from the Jerusalem area with SMED-SL. Additionally, we studied two patients from Algerian and Pakistani ancestry and the parents of the first Jewish patients reported.(1) Using a homozygosity mapping strategy, we located a candidate region on chromosome 1q23 spanning 2.4 Mb. The position of the Discoidin Domain Receptor 2 (DDR2) gene within the candidate region and the similarity of the ddr2 knockout mouse to the SMED patients' phenotype prompted us to study this gene(6). We identified three missense mutations c.2254 C > T [R752C], c. 2177 T > G [I726R], c.2138C > T [T713I] and one splice site mutation [IVS17+1g > a] in the conserved sequence encoding the tyrosine kinase domain of the DDR2 gene. The results of this study will permit an accurate early prenatal diagnosis and carrier screening for families at risk.