Folding and assembly of type X collagen mutants that cause metaphyseal chondrodysplasia-type schmid. Evidence for co-assembly of the mutant and wild-type chains and binding to molecular chaperones.
Schmid metaphyseal chondrodysplasia results from mutations within the COOH-terminal globular domain (NC1) of type X collagen, a short chain collagen expressed in the hypertrophic region of the growth plate cartilage. Previous in vitro studies have proposed that mutations prevent the association of the NC1 domain of constituent chains of the trimer based upon a lack of formation of a trimeric structure that is resistant to dissociation with sodium dodecyl sulfate. To examine the effect of mutations on folding and assembly within a cellular context, bovine type X cDNAs containing analogous disease causing mutations Y598D, N617K, W651R, and wild-type were expressed in semi-permeabilized cells. We assessed trimerization of the mutant chains by their ability to form a collagen triple helix. Using this approach, we demonstrate that although there is an apparent lower efficiency of association of the mutant NC1 domains, they can drive the formation of correctly aligned triple helices with the same thermal stability as the wild-type collagen. When epitope-tagged mutant and wild-type collagen were co-expressed, heterotrimers could be detected by sequential immunoprecipitation. Both wild-type and mutant type X chains were found in association with the molecular chaperones protein disulfide isomerase and Hsp 47. The implications of these findings on the likely mechanism of Schmid metaphyseal chondrodysplasia will be discussed. (+info)
Structural and functional characterization of the mouse Sox9 promoter: implications for campomelic dysplasia.
Mutations in SOX9 cause campomelic dysplasia (CD), a dominant skeletal dysmorphology and XY sex reversal syndrome. The CD phenotype is sensitive to dosage and expression levels of SOX9. Sox9 is expressed during chondrocyte differentiation and is up-regulated in male and down-regulated in female genital ridges during sex differentiation. In order to study the sex- and tissue-specific regulation of Sox9, we have defined the transcription start site and characterized the mouse Sox9 promoter region. The Sox9 proximal promoter shows moderately high nucleotide similarity between mouse and human. Transient transfection experiments using various deletion constructs of the 6.8 kb upstream region of mouse Sox9 fused to a luciferase reporter showed that the interval between 193 and 73 bp from the transcription start site is essential for maximal promoter activity in cell lines and in primary male and female gonadal somatic cells and liver cells isolated from 13.5 d.p.c. mouse embryos. This minimal promoter region was shown by DNase I hypersensitive site assay to be in an 'open' state of chromatin structure in gonads of both sexes, but not in the liver. Promoter activity was higher in testis than in ovary and liver, but deletion of the region from -193 to -73 bp abolished this difference. We conclude that the proximal promoter region is in part responsible for the sex- and tissue-specific expression of the Sox9 gene and that more distal positive and negative elements contribute to its regulation in vivo, consistent with the observation that translocations upstream from SOX9 can result in campomelic dysplasia. (+info)
Can transvaginal fetal biometry be considered a useful tool for early detection of skeletal dysplasias in high-risk patients?
OBJECTIVE: To evaluate the possibility of an early diagnosis of skeletal dysplasias in high-risk patients. METHODS: A total of 149 consecutive, uncomplicated singleton pregnancies at 9-13 weeks' amenorrhea, with certain menstrual history and regular cycles, were investigated with transvaginal ultrasound to establish the relationship between femur length and menstrual age, biparietal diameter and crown-rump length, using a polynomial regression model. A further eight patients with previous skeletal dysplasias in a total of 13 pregnancies were evaluated with serial examinations every 2 weeks from 10-11 weeks. RESULTS: A significant correlation between femur length and crown-rump length and biparietal diameter was found, whereas none was observed between femur length and menstrual age. Of the five cases with skeletal dysplasias, only two (one with recurrent osteogenesis imperfecta and one with recurrent achondrogenesis) were diagnosed in the first trimester. CONCLUSIONS: An early evaluation of fetal morphology in conjunction with the use of biometric charts of femur length against crown-rump length and femur length against biparietal diameter may be crucial for early diagnosis of severe skeletal dysplasias. By contrast, in less severe cases, biometric evaluation appears to be of no value for diagnosis. (+info)
COL9A3: A third locus for multiple epiphyseal dysplasia.
Multiple epiphyseal dysplasia (MED), an autosomal dominant osteochondrodysplasia, is a clinically and genetically heterogeneous disorder characterized by mild short stature and early-onset osteoarthritis. The phenotypic spectrum includes the mild Ribbing type, the more severe Fairbank type, and some unclassified forms. Linkage studies have identified two loci for MED. One of these, EDM1, is on chromosome 19, in a region that contains the cartilage oligomeric matrix protein (COMP) gene. Mutations have been identified in this gene in patients with the Ribbing type, the Fairbank type, and unclassified forms of MED. The second locus, EDM2, maps to chromosome 1, in a region spanning COL9A2. Recently, a splice-site mutation was found in COL9A2, causing skipping of exon 3 in one family with MED. Because of the exclusion of the EDM1 and EDM2 loci in some families, the existence of a third locus has been postulated. We report here one family with MED, evaluated clinically and radiologically and tested for linkage with candidate genes, including COMP, COL9A1, COL9A2, and COL9A3. No linkage was found with COMP, COL9A1, or COL9A2, but an inheritance pattern consistent with linkage was observed with COL9A3. Mutation analysis of COL9A3 identified an A-->T transversion in the acceptor splice site of intron 2 in affected family members. The mutation led to skipping of exon 3 and an in-frame deletion of 12 amino acid residues in the COL3 domain of the alpha3(IX) chain and thus appeared to be similar to that reported for COL9A2. This is the first disease-causing mutation identified in COL9A3. Our results also show that COL9A3, located on chromosome 20, is a third locus for MED. (+info)
Chondrodiatasis in a patient with spondyloepimetaphyseal dysplasia using the Ilizarov technique: successful correction of an angular deformity with ensuing ossification of a large metaphyseal lesion. A case report.
Distraction through the physis (chondrodiatasis) is a controversial technique with unpredictable results. However, it has been used in the past for the lengthening and correction of angular deformities of long bones. We report the case of an 11-year-old patient with spondyloepimetaphyseal dysplasia (SEMD) who presented with a severe recurvatum deformity of the left proximal tibia secondary to collapse of the tibial plateau into a large metaphyseal cystic lesion. Using the chondrodiatasis technique with a percutaneously applied Ilizarov circular frame, we were able to correct this deformity. Surprisingly, healing and ossification of the metaphyseal lesion was simultaneously observed at the end of the treatment, a finding which, to the best of our knowledge, has not been previously reported. (+info)
Multiple disc herniations in spondyloepiphyseal dysplasia tarda. A case report.
Spondyloepiphyseal dysplasia (SED) tarda is a group of inherited dysplasias in which the spine and the epiphyses of long bones are affected from late childhood. A 19-year-old male was diagnosed as SED tarda. He had a thoracic and then lumbar disc herniations which were separated by a 4-year interval. Surgical excision was performed for each disc herniation. This is the first case report of multiple disc herniations in SED. (+info)
The orthopaedic aspects of multiple epiphyseal dysplasia.
Five cases of multiple epiphyseal dysplasia (MED) were treated from 1985-1996 at the Orthopaedics and Trauma Department of SSK Izmir Educational Hospital. Four patients were female and one was male. The pedigrees of the first two female patients had the same features of inter-related marriages. The patients have been followed up for 5.5-11 years (average of 7.5 years). Surgical operations were mostly required in the lower limbs. Problems in the hips required adductor myotomy, the Soutter procedure, total hip replacement, and pertrochanteric extension osteotomy. Management of the knees required supracondylar shortening and extension osteotomy of the femur, high tibial extension osteotomy, debridement of the knee joint with removal of osteophytes, ogleotomy of the patellar lengthening of the knee flexors and posterior capsulotomy. Interphalangeal arthrodesis for hammer toes, extension osteotomy of the head of the first metatarsals, and Kellers operation were carried out in the foot. In the upper limb decompression and anterior transposition of the ulnar nerve, debridement of the elbow joint, extension and valgus osteotomy of the distal radius, and extension osteotomy of the head of the first metacarpal were required. (+info)
Interaction of collagen alpha1(X) containing engineered NC1 mutations with normal alpha1(X) in vitro. Implications for the molecular basis of schmid metaphyseal chondrodysplasia.
Collagen X is a short-chain homotrimeric collagen expressed in the hypertrophic zone of calcifying cartilage. The clustering of mutations in the carboxyl-terminal nonhelical NC1 domain in Schmid metaphyseal chondrodysplasia (SMCD) suggests a critical role for NC1 in collagen X structure and function. In vitro collagen X DNA expression, using T7-driven coupled transcription and translation, demonstrated that although alpha1(X) containing normal NC1 domains can form electrophoretically stable trimers, engineered SMCD NC1 missense or premature termination mutations prevented the formation of electrophoretically stable homotrimers or heterotrimers when co-expressed with normal alpha1(X). To allow the detection of more subtle interactions that may interfere with assembly but not produce SDS-stable final products, we have developed a competition-based in vitro co-expression and assembly approach. Our studies show that alpha1(X) chains containing SMCD mutations reduce the efficiency of normal alpha1(X) trimer assembly, indicating that interactions do occur between mutant and normal NC1 domains, which can impact on the formation of normal trimers. This finding has important implications for the molecular pathology of collagen X mutations in SMCD. Although we have previously demonstrated haploinsufficiency as one in vivo mechanism (Chan, D., Weng, Y. M., Hocking, A. M., Golub, S., McQuillan, D. J., and Bateman, J. F. (1998) J. Clin. Invest. 101, 1490-1499), the current study suggests dominant interference is also possible if the mutant protein is expressed in vivo. Furthermore, we establish that a conserved 13-amino acid aromatic motif (amino acids 589-601) is critical for the interaction between the NC1 domains, suggesting that this region may initiate assembly and the other NC1 mutations interfered with secondary interactions important in folding or in stabilizing the assembly process. (+info)