A novel mutation in FGFR-3 disrupts a putative N-glycosylation site and results in hypochondroplasia

Fibroblast growth factor receptor 3 (FGFR3) is a glycoprotein that belongs to the family of tyrosine kinase receptors. Specific mutations in the FGFR3 gene are associated with autosomal dominant human skeletal disorders such as hypochondroplasia, achondroplasia, and thanatophoric dysplasia. Hypochondroplasia (HCH), the mildest form of this group of short-limbed dwarfism disorders, results in approximately 60% of cases from a mutation in the intracellular FGFR3-tyrosine kinase domain. The remaining cases may either be caused by defects in other FGFR gene regions or other yet unidentified genes. We describe a novel HCH mutation, the first found outside the common mutation hot spot of this condition. This point mutation, an N328I exchange in the extracellular Ig domain III of the receptor, seems to be unique as it affects a putative N-glycosylation site that is conserved between different FGFRs and species. The amino acid exchange itself most probably has no impact on the three-dimensional structure of the receptor domain, suggesting that the phenotype is the result of altered receptor glycosylation and its pathophysiological consequences.

Blomstrand osteochondrodysplasia: three novel cases and histological evidence for heterogeneity

Blomstrand osteochondrodysplasia (BOCD) is a rare, autosomal recessive, lethal skeletal dysplasia characterized by generalized osteosclerosis and advanced skeletal maturation. The histopathological characteristics of three novel cases (two isolated cases and a sib-pair) of BOCD are presented and correlated with the clinical and radiographical findings, and the relevant literature is reviewed. The results of our study confirm the existence of two separate types of BOCD, which we propose naming type I: the severe, 'classical' form, and type II: a less severe form.

Jeune syndrome and liver disease: report of three cases treated with ursodeoxycholic acid

Three children with Jeune syndrome (asphyxiating thoracic dystrophy) had clinical and laboratory evidence of liver disease. In two patients the disease evolved to biliary cirrhosis, whereas in the third it was recognized when extensive fibrosis was developing. In the three patients, treatment with ursodeoxycholic acid appeared to control the progression of the hepatic dysfunction.

Blomstrand chondrodysplasia: a lethal sclerosing skeletal dysplasia. Case report and review

We report a female stillborn with typical clinical, radiological, and anatomopathological features of Blomstrand chondrodysplasia. The main findings in this lethal osteochondrodysplasia are osteosclerosis and advanced skeletal maturation. Autosomal recessive inheritance has been proposed because of parental consanguinity of affected siblings in all reported cases, including this one. Histopathological study of the bones confirmed the advanced skeletal maturation radiological features. We also review this rare lethal osteochondrodysplasia.

The histological spectrum of subperiosteal fibrocartilaginous pseudotumor of long bone (focal fibrocartilaginous dysplasia)

Clinicopathological features in six cases of focal fibrocartilaginous dysplasia (FFCD) which involved either the tibia (n = 4) or the femur (n = 2) were reviewed. All cases presented clinical and radiological characteristic features, and histopathological findings were analyzed in five of the six cases. The subject group comprised three boys and three girls, ages ranged from 12 to 18 months. Histologically, the individual lesions showed regional variation in cellularity, amount of fibrous and cartilaginous components. Paucicellular areas were mainly composed of dense fibrous tissue while more cellular areas contained foci of fibrocartilaginous element. The chondrocytes and stellate cells around cartilaginous area were positive for S-100 protein. One case contained both hyaline and fibrocartilage, and architecturally mimicked normal tendinous insertion. One case, which involved proximal tibia, was purely composed of fibrous tissue without fibrocartilage. All cases formed undulating and irregular borders against underlying cortical bone. Histopathologically variable spectrum suggests a strong possibility of undergoing transition from initial cellular and cartilagnous to late paucicellular, fibrous phase. Although any evidence that can explain basic pathogenesis or prognostic histological parameter is lacking, we believe that the term FFCD is not relevant because the presence of fibrocartilage is not an essential feature, and it can cause confusion with other pathological processes. We propose the term 'subperiosteal fibrocartilaginous pseudotumor of long bone' for this unique clinicopathological entity with which heterologous cartilaginous element can be associated.

A frame-shift mutation in the type I parathyroid hormone (PTH)/PTH-related peptide receptor causing Blomstrand lethal osteochondrodysplasia

Blomstrand osteochondrodysplasia (BOCD) is a rare lethal skeletal dysplasia characterized by accelerated endochondral and intramembranous ossification. Comparison of the characteristics of BOCD with type I PTH/PTH-related peptide (PTHrP) receptor-ablated mice reveals striking similarities that are most prominent in the growth plate. In both cases, the growth plate is reduced in size due to a strongly diminished zone of resting cartilage and the near absence of columnar arrangement of proliferating chondrocytes. This overall similarity suggested that an inactivating mutation of the PTH/PTHrP receptor might be the underlying genetic defect causing BOCD. Indeed, inactivating mutations of the PTH/PTHrP receptor have been recently identified in two cases of BOCD. We describe here a novel inactivating mutation in the PTH/PTHrP receptor. Sequence analysis of all coding exons of the type I PTH/ PTHrP receptor gene and complementary DNA of a case with BOCD identified a homozygous point mutation in exon EL2 in which one nucleotide (G at position 1122) was absent. The mutation was inherited from both parents, supporting the autosomal recessive nature of the disease. The missense mutation resulted in a shift in the open reading frame, leading to a truncated protein that completely diverged from the wild-type sequence after amino acid 364. The mutant receptor, therefore, lacked transmembrane domains 5, 6, and 7; the connecting intra- and extracellular loops; and the cytoplasmic tail. Functional analysis of the mutant receptor in COS-7 cells and of dermal fibroblasts obtained from the case proved that the mutation was indeed inactivating. Neither the transiently transfected COS-7 cells nor the dermal fibroblasts responded to a challenge with PTH or PTHrP with a rise in intracellular cAMP levels, in sharp contrast to control cells. Our results provide further evidence that BOCD is caused by inactivating mutations of the type I PTH/PTHrP receptor and underscore the importance of this receptor in mammalian skeletal development.

Prenatal diagnosis of thoracopelvic dysplasia. A case report

BACKGROUND

Thoracopelvic dysplasia, a variant of asphyxiating thoracic dysplasia (Jeune syndrome), is an uncommon skeletal disorder characterized by a small thorax, pelvic abnormalities and other complex, combined anomalies, including hypomelia, polydactyly and renal anomalies.

CASE

A 32-year-old woman, gravida 1, para 0, was referred at 27 weeks' gestation due to polyhydramnios. Sonography revealed hydramnios, low fetal thoracic circumference (TC) and abdominal circumference (AC) ratio (0.78), skull and skin edema, increased nuchal translucency (7 mm), micrognathia, low-set ears, left cardiac deviation (66 degrees), overriding fingers, and club and rock-buttock feet. Amniocentesis revealed a normal karyotype (46, XY). Asphyxiating thoracic dysplasia was considered. At 40 weeks' gestation, a male infant was delivered vaginally. Besides the prenatal findings, cryptorchidism and high-arched palate were noted. Radiography of the infant revealed a narrow, funnel-shaped thorax and small pelvis with short, flared iliac bones; poorly developed acetabulum; and small, shallow sciatic notch. No dyspnea was observed at five months postpartum.

CONCLUSION

Thoracopelvic dysplasia should be considered when a low TC/AC ratio (< 0.8) is observed. In this case the final diagnosis was made after detailed exclusion of other disorders combined with observation of a small thorax. Prenatal diagnosis of thoracopelvic dysplasia is possible.

The knee joint in diastrophic dysplasia. A clinical and radiological study

We examined clinically and radiologically the knees of 46 patients (27 females and 19 males) with diastrophic dysplasia. The age of the patients varied from newborn to 38 years. A total of 18 patients was followed during their growth until adolescence. The knees of two legally aborted fetuses appeared on examination to be macroscopically normal and congruous. Excessive valgus deformity of the tibiofemoral weight-bearing angle with a mean of 14 degrees was noted in infancy. Most of the patients had marked instability of the knees. The range of movement of the knee began to decrease before the age of five years. There were signs of early degeneration and deformation of the bony epiphyses before the age of six years. The patellofemoral joint was abnormal from an early age. A marked patella infera, often associated with a lateral position of the patella with bony fragmentation, was noted. The knee in diastrophic dysplasia is basically unstable, showing early deformation of the subchondral bone and degeneration of the joint.

Spondylo-epi-metaphyseal dysplasia with normal stature: a case followed from infancy to skeletal maturity

Spondylo-epi-metaphyseal dysplasia is a rare skeletal dysplasia showing radiographic abnormalities in the epiphyses and metaphyses of the long and short tubular bones, and in the spine. There are very few reports of a case followed throughout the entire growth period. Here we report the case of a Japanese girl followed from 1 month old to skeletal maturity at 16 years old. She developed progressive kyphoscoliosis at 7 years old, and underwent a surgical correction of the spine at 14 years old. The diagnosis of spondylo-epi-metaphyseal dysplasia was made from examining all the follow-up radiographs showing abnormalities in the spine, long bones and hands involving epiphyses and metaphyses. She had normal stature--a rare finding in this condition.

Spinal manifestations of skeletal dysplasias

Skeletal dysplasias, disorders of abnormal bone and cartilage development, are a heterogeneous group, each disorder with its own genetics, prevalence, prognosis, and treatment. More than 150 distinct conditions have been identified. Despite their obvious differences, the osteochondrodysplasias share many clinical and radiographic features. These patients present to the orthopedic surgeon for evaluation of disproportionate short stature, which may be apparent at birth or manifest itself only with further growth. This article discusses bone dysplasias commonly associated with spinal abnormalities. Spinal pathology can lead to deformity, neurologic sequelae, pain, and cardiopulmonary compromise and further contribute to short stature.

Dysplasia epiphysealis hemimelica of the scaphoid bone

We report a rare case of dysplasia epiphysealis hemimelica (DEH) in the wrist of a 7-year-old boy. Clinical, radiological and histopathological manifestations are discussed. The correct diagnosis of DEH, however, was made by the confrontation of the radiological and pathological data. The radiologist should inform the pathologist correctly about the imaging findings in order to avoid misdiagnosis of the lesion as osteochondroma.

Unusual fan shaped ossification in a female fetus with radiological features of boomerang dysplasia

We report on a female fetus of 24 weeks whose clinical and radiological findings were compatible with boomerang dysplasia (BD). However, histopathology was unusual with a lateral fan shaped diaphyseal ossification. This has never been described either in typical atelosteogenesis I (AT-I) or in BD. The purpose of this report is to find out if this condition is a separate lethal bone dysplasia or another histological feature of the nosological group of AT-I and BD.

A new syndrome of spondyloepimetaphyseal dysplasia, eczema and hypogammaglobulinaemia

We describe a female infant with a combination of very short stature, severe eczema and IgG deficiency causing recurrent infections in infancy. The radiological features of this condition are presented in the neonatal period, at the age of 5 months and at 2 years and 6 months. We propose that this condition is a previously undescribed type of spondyloepimetaphyseal dysplasia.

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.

[A case of tracheobronchopathia osteoplastica discovered incidentally by hypoxemia following the operation]

An 85-year-old woman was found to have tracheobronchopathia osteoplastica incidentally following an operation for left breast cancer. She entered the ICU because of impaired sputum expectoration and hypoxemia. For the purpose of bronchial toilet, bronchofiberscopy was performed under general anesthesia. Numerous nodular elevated lesions were found on all sides of trachea and lobar bronchi except at the membranous part. Transbronchial forceps biopsy showed squamous metaplasia of the mucosa and formation of lamellar bone in the submucosal tissue. The diagnosis was finally confirmed as tracheobronchopathia osteoplastica from these two findings. Although anesthesiologists rarely encounter this disease in their daily practice, it is necessary to keep tracheobronchopathia osteoplastica in their mind as an airway disease.

Autosomal recessive syndrome of growth and mental retardation, seizures, retinal abnormalities, and osteodysplasia with similarity to the Gurrieri syndrome

We report on two sibs, brother and sister, with a multiple congenital anomaly/mental retardation syndrome consisting of severe growth and mental retardation, seizures, retinal abnormalities, osteodysplasia, brachydactyly, prognathism, and dental malocclusion. These clinical findings were present in both patients and seem to be consistent with the phenotype of the Gurrieri syndrome. The new features described in these sibs could expand the clinical spectrum of the Gurrieri syndrome and confirm the existence of this rare autosomal recessive condition.

Recurrence of fibrochondrogenesis in a consanguineous family

A second case of fibrochrondrogenesis in a consanguineous family is described. The fact that both sexes are affected in this family supports autosomal recessive inheritance.

X-linked recessive spondyloepiphyseal dysplasia tarda. Clinical and radiographic evolution in a 6-generation kindred and review of the literature

We characterize the clinical and radiographic evolution of X-linked recessive spondyloepiphyseal dysplasia tarda (SEDT) in a 6-generation kindred from Arkansas (SEDT(AK)). Our observations show the natural progression of SEDT(AK) and enable carrier detection by radiographic study. We find that, SEDT(AK) manifests as a postnatal defect. Affected hemizygous males can have radiographically normal vertebrae at birth. The pathogenesis seems to involve a developmental disturbance in endochondral bone formation that is reflected most dramatically in vertebrae by a radiographically inapparent ring apophysis. This defect leads to distinctive malformation of the anterior margins of the lumbar vertebrae during childhood. Subsequently, there is degeneration of intervertebral discs and destruction of spinal facet joints. In the femur, the head, neck, and distal condyles are abnormally shaped and become distorted so that osteoarthritis of the hip is not uncommon. Obligate carrier females heterozygous for the SEDT(AK) gene defect demonstrate several similar but more subtle skeletal abnormalities beginning in early adult life. These women seem to be troubled frequently by arthralgia by middle age. The cumulative findings in SEDT(AK) implicate a defect in a gene at Xp22.2-22.1 that engenders a relatively mild disturbance in endochondral bone formation, especially in the axial skeleton. Accounts of large, well-characterized SEDT kindreds remain essential to appreciate fully any interfamily variability of disease expression and to understand better the pathogenesis of the SEDT defect on the X chromosome.

Trinucleotide expansion mutations in the cartilage oligomeric matrix protein (COMP) gene

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are two human autosomal dominant skeletal dysplasias characterized by variable short stature, joint laxity and early-onset degenerative joint disease. Both disorders can result from mut-ations in the gene for cartilage oligomeric matrix protein (COMP), an extracellular matrix glycoprotein. About one-third of PSACH cases result from heterozygosity for deletion of one codon within a very short triplet repeat, (GAC)5, which encodes five consecutive aspartic acid residues within the calmodulin-like region of the COMP protein. We have identified two expansion mut-ations in this repeat: an MED patient carrying a (GAC)6allele and a PSACH patient carrying a (GAC)7allele. These are among the shortest disease-causing triplet repeat expansion mutations described thus far, and are the first identified in a GAC repeat. A unique feature of this sequence is that expansion as well as shortening of the repeat can cause the same disease. In cartilage, both patients have rough endoplasmic reticulum inclusions in chondrocytes. The inclusions are also present in tendon tissue and can be reproduced in cultured tendon cells, suggesting that the pathophysiology of disease is similar in both cartilage and tendon.

Lethal osteosclerotic osteochondrodysplasia with platyspondyly, metaphyseal widening, and intracellular inclusions in sibs

We report on a previously undescribed form of lethal osteosclerotic skeletal dysplasia in sibs from nonconsanguineous parents. Radiographic findings included increased density in the base of the skull, clavicles, vertebrae, ribs, and the metaphyseal regions of the long bones. There was midface hypoplasia, a large anterior fontanel, micrognathia, and hypoplastic, wafer-thin vertebrae. The clavicles, ribs, metacarpals, metatarsals, and phalanges were especially thickened and widened. The long bones were shortened with flared metaphyses. Chondroosseous morphology of resting cartilage and growth plate was relatively normal, but there was hypercellular cortical and trabecular bone, and marrow fibrosis. Ultrastructurally, the resting chondrocytes, osteoblasts, and nonhematopoietic marrow cells had dilated rough endoplasmic reticulum (inclusion bodies). The radiographic and morphologic characteristics in this case are unique and differ from those seen in other previously reported lethal osteosclerotic skeletal dysplasias.

Predictive value of fetal ultrasonography in the diagnosis of a lethal skeletal dysplasia

BACKGROUND

Certain ultrasonographic findings identified in a fetus suspected of having a skeletal dysplasia may be predictive of a lethal outcome.

METHODS

We evaluated 27 fetuses suspected of having a skeletal dysplasia using targeted ultrasonography between 16 and 31 weeks' gestation. Clinical examination and skeletal radiography were done after delivery.

RESULTS

A skeletal dysplasia was confirmed and a diagnosis established in all but one case. The skeletal dysplasia was lethal in 23 cases and, in each case, the outcome was accurately predicted prenatally; however, three of the infants survived several months. In 11 of the 23 cases (48%), the specific diagnosis was correctly determined before birth. Ultrasonographic findings not considered to reflect a lethal outcome, were accurately predicted in two other cases. In an additional two, sonographic examination suggested a lethal osteochondrodysplasia, though both survived. Findings consistent with a lethal skeletal dysplasia included a femur length < 1st centile, combined with either a bell-shaped thorax, decreased bone echogenicity, or both. Using these criteria provided a positive-predictive value for neonatal deaths of 80% (20/25), and 92% (23/25) if the three that died in infancy were included.

CONCLUSIONS

In the fetus suspected of having a skeletal dysplasia, certain findings on targeted ultrasonography frequently are predictive of a lethal outcome; the ability to predict this appears greatest when more than one of these abnormalities is present.

Retention of cartilage oligomeric matrix protein (COMP) and cell death in redifferentiated pseudoachondroplasia chondrocytes

Cartilage oligomeric matrix protein (COMP) is a large extracellular glycoprotein that is found in the territorial matrix surrounding chondrocytes. Two skeletal dysplasias, pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (EDM1) are caused by mutations in the calcium binding domains of COMP. In this study, we identified two PSACH mutations and assessed the effect of these mutations on redifferentiated chondrocyte structure and function. We confirmed, in vitro, that COMP is retained in enormous cisternae of the rough endoplasmic reticulum (rER) and relatively absent in the PSACH matrix. The rER accumulation may compromise chondrocyte function, leading to chondrocyte death. Moreover, while COMP appears to be deficient in the PSACH matrix, the matrix appeared to be normal but the over-all quantity was reduced. These results suggest that the abnormality in linear growth in PSACH may result from decreased chondrocyte numbers which would also affect the amount of matrix produced.

Development of avian tibial dyschondroplasia: gene expression and protein synthesis

Age-dependent gene expression and protein synthesis associated with chondrocyte differentiation were evaluated in the epiphyseal growth plates of normal and tibial dyschondroplasia (TD)-afflicted chickens. In the normal growth plate, collagen type II gene is expressed mainly by chondrocytes at the upper zone of the growth plate and by the chondrocytes in the articular cartilage. Collagen type X and osteopontin (OPN) genes are expressed in the lower zone of the growth plate and in the zone of cartilage-to-bone transition. No age-dependent changes in the pattern of OPN and collagen type II or X gene expression were observed up to 20 days of age. In the TD-afflicted growth plates, the lesion is enlarged with age, and chondrocytes expressing the collagen type II gene were observed in the hypertrophic zone as early as 8 days posthatching. Abnormal expression of OPN and collagen type X genes was also observed starting at 13 days of age. At day 20, the entire TD lesion-which was significantly enlarged-was surrounded by collagen type II, collagen type X, and OPN expressing cells. The level of OPN in TD was reduced with increasing age, and at 20 days almost no OPN could be detected in either the upper or the lower hypertrophic zones. The level of bone sialoprotein (BSP) also diminished with increasing age in the TD growth plates. In contrast to OPN, the age-dependent reduction in BSP levels was mainly in the lower hypertrophic zone (LHZ), and at 20 days of age, BSP was barely detected in the LHZ, whereas in the upper hypertrophic zone, the levels of BSP were similar to those in normal growth plate. In summary, our results suggest that the primary event of the TD lesion occurs in cells of proliferative phenotype within the hypertrophic zone. These cells divide and form the TD lesion, which consists of cells that do not express the genes associated with hypertrophy.

Achondroplasia, hypochondroplasia and thanatophoric dysplasia: clinically related skeletal dysplasias that are also related at the molecular level

This is the second of three articles on modern genetic concepts of a number of syndromes and disorders. Three short limb skeletal dysplasias with additional abnormalities of the skull are discussed. All are caused by mutations on fibroblast growth factor receptor 3 (FGFR3). A pathogenetic hypothesis is proposed to explain differences in the severity of short stature, midface deficiency, and craniosynostosis.