The lethal osteochondrodysplasias

Integrated analysis of COL2A1 variant data and classification of type II collagenopathies

The COL2A1 gene encodes the alpha-1 chain of type II procollagen. Type II collagen, comprised of three identical alpha-1 chains, is the major component of cartilage. COL2A1 gene variants are the etiologies of genetic diseases, termed type II collagenopathies, with a wide spectrum of clinical presentations. To date, at least 460 distinct COL2A1 mutations, identified in 663 independent probands, and 21 definite disorders have been reported. Nevertheless, a well-defined genotype-phenotype correlation has not been established, and few hot spots of mutation have been reported. In this study, we analyzed data of COL2A1 variants and clinical information of patients obtained from the Leiden Open Variation Database 3.0, as well as the currently available relevant literature. We determined the characteristics of the COL2A1 variants and distributions of the clinical manifestations in patients, and identified four likely genotype-phenotype correlations. Moreover, we classified 21 COL2A1-related disorders into five categories, which may assist clinicians in understanding the essence of these complex phenotypes and prompt genetic screening in clinical practice.

Achondroplasia: a comprehensive clinical review

Achondroplasia is the most common of the skeletal dysplasias that result in marked short stature (dwarfism). Although its clinical and radiologic phenotype has been described for more than 50 years, there is still a great deal to be learned about the medical issues that arise secondary to this diagnosis, the manner in which these are best diagnosed and addressed, and whether preventive strategies can ameliorate the problems that can compromise the health and well being of affected individuals. This review provides both an updated discussion of the care needs of those with achondroplasia and an exploration of the limits of evidence that is available regarding care recommendations, controversies that are currently present, and the many areas of ignorance that remain.

A common pathomechanism in GMAP-210- and LBR-related diseases

Biallelic loss-of-function mutations in TRIP11, encoding the golgin GMAP-210, cause the lethal human chondrodysplasia achondrogenesis 1A (ACG1A). We now find that a homozygous splice-site mutation of the lamin B receptor (LBR) gene results in the same phenotype. Intrigued by the genetic heterogeneity, we compared GMAP-210- and LBR-deficient primary cells to unravel how particular mutations in LBR cause a phenocopy of ACG1A. We could exclude a regulatory interaction between LBR and GMAP-210 in patients' cells. However, we discovered a common disruption of Golgi apparatus architecture that was accompanied by decreased secretory trafficking in both cases. Deficiency of Golgi-dependent glycan processing indicated a similar downstream effect of the disease-causing mutations upon Golgi function. Unexpectedly, our results thus point to a common pathogenic mechanism in GMAP-210- and LBR-related diseases attributable to defective secretory trafficking at the Golgi apparatus.

Perinatal imaging findings and molecular genetic analysis of thanatophoric dysplasia type 1 in a fetus with a c.2419T>G (p.Ter807Gly) (X807G) mutation in FGFR3

OBJECTIVE

We present perinatal imaging findings and molecular genetic analysis of thanatophoric dysplasia type I (TD1) in a fetus.

CASE REPORT

A 28-year-old woman was referred for genetic counseling at 22 weeks of gestation because of abnormal prenatal ultrasound findings. Level II ultrasound examination revealed a narrow chest, shortened and curved long limbs, protrusion of the abdomen, and macrocephaly. A tentative diagnosis of TD1 was made. After genetic counseling, the pregnancy was terminated and a malformed fetus was delivered. Postnatal radiography findings were consistent with the diagnosis of TD1, with additional findings of short ribs, platyspondyly, and horizontal acetabular roofs. Molecular genetic analysis using umbilical cord tissue revealed a heterozygous mutation of c.2419T>G (p.Ter807Gly) (X807G) in the fibroblast growth factor receptor 3 gene (FGFR3).

CONCLUSION

A second-trimester fetus with a heterozygous c.2419T>G mutation in FGFR3 may present characteristic ultrasound and X-ray findings of TD1.

Protein-losing enteropathy with intestinal lymphangiectasia in skeletal dysplasia with Lys650Met mutation

Protein-losing enteropathy is a primary or secondary manifestation of a group of conditions, and etiologies which are broadly divisible into those with mucosal injury on the basis of inflammatory and ulcerative conditions, mucosal injury without erosions or ulcerations, and lymphatic abnormalities. We describe the first case of protein-losing enteropathy in a pediatric patient, with severe skeletal dysplasia consistent with thanatophoric dysplasia type I and DNA analysis that revealed a c.1949A>T (p.Lys650Met) in exon 15 of the FGFR3 gene. She presented with protein-losing enteropathy in her 6th month. Post-mortem examination revealed lymphangiectasia in the small intestine. To our knowledge, this is the first report of intestinal lymphangiectasia as a complication of skeletal dysplasia resulting in severe protein-losing enteropathy. © 2016 Wiley Periodicals, Inc.

Increased first-trimester nuchal translucency associated with thanatophoric dysplasia type 1

Thanatophoric dysplasia (TD) is the most frequent form of lethal skeletal dysplasia. Prenatal diagnosis is commonly accomplished in the second-trimester scan, but occasionally TD is found to be associated with increased nuchal translucency (NT) at first-trimester screening for aneuploidies. TD may not be clearly distinguished from the other skeletal dysplasias. A definite diagnosis can be established by molecular genetic analysis to find out the abnormal mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. We reported a case of TD type 1 detected by first-trimester NT measurement, and confirmed by molecular analysis of FGFR3 gene using high-resolution melting analysis.

Re-alignment-procedures for skeletal dysplasia in three patients with genetically diverse syndromes

OBJECTIVE

Disruption to endochondral ossification leads to delayed and irregular bone formation and can result in a heterogeneous group of genetic disorders known as osteochondrodysplasias. These genetic disorders arise through disturbances in the complex processes of skeletal growth causing development of unsightly skeletal deformities. METHODS : Each syndrome was diagnosed on the basis of detailed clinical and radiographic assessment. Lower limb deformities were the prime presenting feature.

RESULTS

Here are presented three patients with diverse genetic syndromes, namely Wolcott-Rallison syndrome (WRS), Kniest dysplasia (KD) and Desbuquois dysplasia (DS). Genetic testing was performed in the patients with WRS and DS. The diagnosis of KD was made purely on a clinical and radiographic basis. Variable orthopaedic interventions to realign these patients' lower limbs were implemented with the aim of improving their balance and gait.

CONCLUSIONS

The aim of this paper is twofold. The first part is to outline the importance of diagnosing the causes of various skeletal abnormalities in patients with osteochondrodysplasias by phenotypic and genotypic characterization. The second part is to demonstrate our techniques for surgical corrections in patients with joint laxity and malalignment and show how far techniques for growth modulation, re-alignment and ligament reconstruction have advanced.

TRPV4-associated skeletal dysplasias

Dominant mutations in the TRPV4 gene result in a bone dysplasia family and form a continuous phenotypic spectrum that includes, in decreasing severity, lethal, and nonlethal metatropic dysplasia (MD), spondylometaphyseal dysplasia Kozlowski type (SMDK), and autosomal dominant brachyolmia. Several rare variant phenotypes that have some overlap but deviate in some ways from the general pattern have also been described. The known variant phenotypes are spondyloepiphyseal dysplasia Maroteaux type (Pseudo-Morquio type 2), parastremmatic dysplasia, and familial digital arthropathy with brachydactyly. Interestingly, different TRPV4 mutations have been associated with dominantly inherited neurologic disorders such as congenital spinal muscular atrophy and hereditary motor and sensory neuropathy. Finally, a small number of patients have been identified in whom a TRPV4 mutation results in a phenotype combining skeletal dysplasia with peripheral neuropathy. The TRPV4 gene encodes a regulated calcium channel implicated in multiple and diverse cellular processes. Over 50 different TRPV4 mutations have been reported, with two codons appearing to be mutational hot spots: P799 in exon 15, mostly associated with MD, and R594 in exon 11, associated with SMDK. While most pathogenic mutations tested so far result in activation of the calcium channel in vitro, the mechanisms through which TRPV4 activation results in skeletal dysplasia and/or peripheral neuropathy remain unclear and the genotype-phenotype correlations in this group of disorders remains somewhat mysterious. Since the phenotypic expression of most mutations seems to be relatively constant, careful clinical and radiographic assessment is useful in directing molecular analysis.

Mutations causing Greenberg dysplasia but not Pelger anomaly uncouple enzymatic from structural functions of a nuclear membrane protein

The lamin B receptor (LBR) is an inner nuclear membrane protein with a structural function interacting with chromatin and lamins, and an enzymatic function as a sterol reductase. Heterozygous LBR mutations cause nuclear hyposegmentation in neutrophils (Pelger anomaly), while homozygous mutations cause prenatal death with skeletal defects and abnormal sterol metabolism (Greenberg dysplasia). It has remained unclear whether the lethality in Greenberg dysplasia is due to cholesterol defects or altered nuclear morphology.To answer this question we characterized two LBR missense mutations and showed that they cause Greenberg dysplasia. Both mutations affect residues that are evolutionary conserved among sterol reductases. In contrast to wildtype LBR, both mutations failed to rescue C14 sterol reductase deficient yeast, indicating an enzymatic defect. We found no Pelger anomaly in the carrier parent excluding marked effects on nuclear structure. We studied Lbr in mouse embryos and demonstrate expression in skin and the developing skeletal system consistent with sites of histological changes in Greenberg dysplasia. Unexpectedly we found in disease-relevant cell types not only nuclear but also cytoplasmatic LBR localization. The cytoplasmatic LBR staining co-localized with ER-markers and is thus consistent with the sites of endogeneous sterol synthesis. We conclude that LBR missense mutations can abolish sterol reductase activity, causing lethal Greenberg dysplasia but not Pelger anomaly. The findings separate the metabolic from the structural function and indicate that the sterol reductase activity is essential for human intrauterine development.

Primary failure of eruption and PTH1R: the importance of a genetic diagnosis for orthodontic treatment planning

INTRODUCTION

Primary failure of eruption (PFE) is characterized by nonsyndromic eruption failure of permanent teeth in the absence of mechanical obstruction. Recent studies support that this dental phenotype is inherited and that mutations in PTH1R genes explain several familial cases of PFE. The objective of our study was to investigate how genetic analysis can be used with clinical diagnostic information for improved orthodontic management of PFE.

METHODS

We evaluated a family (n = 12) that segregated an autosomal dominant form of PFE with 5 affected and 7 unaffected persons. Nine available family members (5 male, 4 female) were enrolled and subsequently characterized clinically and genetically.

RESULTS

In this family, PFE segregated with a novel mutation in the PTH1R gene. A heterozygous c.1353-1 G>A sequence alteration caused a putative splice-site mutation and skipping of exon 15 that segregated with the PFE phenotype in all affected family members.

CONCLUSIONS

A PTH1R mutation is strongly associated with failure of orthodontically assisted eruption or tooth movement and should therefore alert clinicians to treat PFE and ankylosed teeth with similar caution-ie, avoid orthodontic treatment with a continuous archwire.

An unclassifiable short rib-polydactyly syndrome with acromesomelic hypomineralization and campomelia in siblings

The short rib-polydactyly (SRP) group are lethal skeletal dysplasias with an autosomal recessive inheritance pattern that can be distinguished on radiological and histological grounds. We report on two consecutive pregnancies complicated by a SRP syndrome with acromesomelic hypomineralization and campomelia that cannot be definitely categorized, yet possesses features of this group of conditions. The skeletal changes observed in both cases included markedly shortened ribs, shortened humeri and femora, limb bowing, absent ossification of the radii, ulnae, tibiae and fibulae, as well as the bony elements of the hands and feet, hypoplastic scapulae and peritoneal calcifications. In one case, the pancreas was abnormal in shape, without a tail and the spleen was not identified. Ectopic splenic tissue and intestinal malrotation were identified and were suggestive of a laterality disorder. Whether these two cases should be considered an atypical form of SRP cannot be completely resolved at this present time and will need to wait on further progress in molecular testing.

First-trimester ultrasound diagnosis of skeletal dysplasia associated with increased nuchal translucency thickness

A series of five cases of skeletal dysplasia is reported in which the diagnosis was reached at the 11-14-week routine ultrasound examination in our referral center. All five cases had increased nuchal translucency thickness (NT) associated with bone abnormalities. We review the current literature on skeletal dysplasia in the first trimester of pregnancy associated with increased NT.

Short rib polydactyly syndrome type 3 with absence of fibulae (Verma-Naumoff syndrome)

Short rib polydactyly syndrome (SRPS) is a group of skeletal dysplasias manifested by short-limb dwarfism, short ribs with thoracic dysplasia and polydactyly. SRPS is an inherited autosomal-recessive disorder with different prenatal sonographic and postnatal clinical, histological and radiologic findings. SRPS type 1 (Saldino-Noonan) and type 3 (Verma-Naumoff) are very similar and frequently get mixed. In this report, we present a case of SRPS with hydrops, thoracic hypoplasia, short limbs and postaxial polydactyly in a 27-week fetus. The visceral findings in the fetus including the central nervous system were normal. The karyotype was 46XY. The prenatal diagnosis was thought to be type 1 because of the absence of fibulae at ultrasonography. However, postmortem autopsy, histologic, and radiologic findings were reviewed and the diagnosis was type 3 SRPS because of absence of visceral anomalies, presence of fan-shaped iliac bones and short tubular bones with metaphyseal widening. We concluded that detailed ultrasonography performed in the prenatal period is very important in the diagnosis and differential diagnosis of SRPS.

A new syndrome of congenital generalized osteosclerosis and bilateral polymicrogyria

We report a 29-week male fetus with healthy consanguineous parents. He showed a severe sclerosing bone disorder affecting all skeletal elements, resulting in insufficient modeling, generalized densification, and fragility of the skeleton. This skeletal dysplasia was associated with an abnormal craniofacial development (hypertelorism, severe microretrognathia, cleft palate, absent epiglottis, reduced number, and mineralization of teeth buds) and abnormal terminal phalanges. Neuropathologic examination showed bilateral fronto-parietal cerebral polymicrogyria. This syndrome appears to represent a new variant of congenital sclerotic bone disorder of unknown origin. Autosomal recessive inheritance is possible.

Prenatal diagnosis of boomerang dysplasia

Boomerang dysplasia, atelosteogenesis type 1 and Piepkorn dysplasia are bone dysplasias with an overlapping clinical spectrum characterized by deficient formation and ossification of specific elements of the skeleton. Typical symptoms include micromelia with diminished ossification, and a characteristic bowed and boomerang-like aspect of the long tubular bones. We report here a new case of boomerang dysplasia, which was detected prenatally in the 16th week of gestation by ultrasound.

Paternal uniparental disomy 14: introducing the "coat-hanger" sign

Paternal uniparental disomy for chromosome 14 (patUPD14) is a rare condition, this being the eighth report. A male infant, born prematurely, was noted to have extremely lax skin and bilateral inguinal hernias. Skin biopsy confirmed the clinical diagnosis of congenital cutis laxa, but this did not explain the limb abnormalities. Radiographic findings (particularly the "coat-hanger" configuration of the ribs on the chest radiograph), suggested a diagnosis of patUPD14, which was confirmed following DNA analysis. The patient died after prolonged respiratory failure. This combination of patUPD14 and congenital cutis laxa has not previously been described. Radiology can play a pivotal role in guiding the geneticist's choice of investigation.

Human fetal bone development: histomorphometric evaluation of the proximal femoral metaphysis

Quantitative data on metaphyseal bone histology during early human development are scarce. In the present study the proximal femoral metaphysis of 35 fetuses and newborns (gestational age 16-35 weeks) was analyzed by histomorphometry. Averaged over the entire metaphyseal area, the relative amount of bone and cartilage was higher in the third compared to the second trimester. Osteoid thickness increased with gestational age, whereas indices of bone resorption decreased. The relative amount of cartilage decreased with increasing distance from the growth plate, whereas the relative amount of bone increased. This was due to trabecular thickening, which occurred at an estimated rate of 3 microm/day in areas close to the growth plate. Despite this rapid rate of net bone gain, osteoid indices were relatively low, indicating that mineralization occurred very rapidly after bone deposition. These observations suggest that modeling, not remodeling, is the predominant mechanism responsible for the development of femoral metaphyseal cancellous bone in utero.

Prenatal diagnosis and genetic analysis of type I and type II thanatophoric dysplasia

Thanatophoric dysplasia (TD) is one of the most common neonatal lethal skeletal dysplasias. Prenatal sonographic and molecular genetic diagnoses of three cases of TD type I (TD1) and one case of TD type II (TD2) are presented here. Two fetuses of TD1 were characterized by polyhydramnios, macrocephaly, short limbs, a narrow thoracic cage and curved short femora, but without a cloverleaf skull at 27 and 31 weeks' gestation, respectively. The third fetus with TD1 was, however, not associated with macrocephaly, polyhydramnios, chest narrowing and severe femoral bowing on prenatal ultrasound at 18 weeks' gestation. The TD2 fetus was characterized by polyhydramnios, short limbs, a narrow thoracic cage, straight short femora, hydrocephalus and a cloverleaf skull at 24 weeks' gestation. Three-dimensional ultrasound was able to enhance the visualization of thickened, redundant skin folds and craniofacial and limb deformities associated with TD. Molecular analysis of the fibroblast growth factor receptor 3 (FGFR3) gene by restriction enzyme digestion analysis and direct sequencing using cultured amniotic fluid cells or cord blood cells revealed a missense mutation of 742C-->T (Arg248Cys) in all cases with TD1 and a missense mutation of 1948A-->G (Lys650Glu) in the case with TD2. The present report shows that adjunctive applications of molecular genetic analysis of the FGFR3 gene and three-dimensional ultrasound are useful for prenatal diagnosis of TD.

Increased mortality in cartilage-hair hypoplasia

BACKGROUND

Cartilage-hair hypoplasia (CHH) is an autosomal recessive chondrodysplasia with severe growth failure and impaired immunity. Impaired immunity may result in increased mortality.

AIMS

To follow a cohort of 120 CHH patients for mortality from 1971 to 1995.

METHODS

The overall and cause specific disease mortality rates in patients with CHH, and the disease mortality rate in 194 parents and 158 non-affected sibs were compared with the national rates.

RESULTS

During follow up seven disease related deaths were observed versus 0.8 expected (standardised mortality ratio 9.3, 95% confidence interval 3.7 to 19). In most cases, the deaths were confined to the younger age groups and associated with defective immunity. The mortality of the parents and the non-affected sibs was similar to that in the general population.

CONCLUSION

The study confirms increased mortality in patients with CHH attributable to defective immunity, especially in children.

Greenberg dysplasia: first reported case with additional non-skeletal malformations and without consanguinity

In 1988 Greenberg et al. reported an association of fetal hydrops with irregular calcification and moth-eaten skeletal dysplasia. Here, we report on the first case of this disorder accompanied by additional malformations (omphalocele, intestinal malrotation, disturbed fingernails and toes, hypolobated lungs) in a German couple without consanguinity (karyotype 46,XY). Sonograpically, the fetus was characterised by tetraphokomelia, severe generalised hydrops, pulmonal hypoplasia and hepato-splenomegaly. Greenberg dysplasia should be considered in differential diagnosis in cases with severe fetal hydrops and phokomelia on antenatal sonography.

Spondylometaphyseal dysplasia: Sedaghatian type

We report a case of spondylometaphyseal dysplasia in an infant who was born to nonconsanguineous Yemeni parents. Radiological findings were consistent with lethal metaphyseal chondrodysplasia (Sedaghatian type). Although all previously reported cases died within 4 days of life, our patient survived 161 days. This reported case was thoroughly investigated for serum calcium, magnesium, zinc, ammonia, phosphate level, alkaline phosphatase, parathormone level, liver and renal function test, TORCH, metabolic screening, skeletal survey, chromosomal studies, muscle enzymes, EEG, computed tomography scan, and magnetic resonance imaging (brain). Genomic DNA analysis of patient and parents were sent to the Faculty de Medicine Xavier Bichat, France, but yet abnormal gene could not be detected.

Lethal osteosclerotic skeletal dysplasia with intracellular inclusion bodies

We report an apparently previously undescribed form of lethal osteosclerotic skeletal dysplasia in a 30-week male fetus with micromelic shortness of the limbs. Radiographic findings at necropsy included increased density in all bones, most marked in the skull, mandible, and pubis. The ribs were very short, abnormally modeled, and wide anteriorly. The vertebrae were posteriorly hypoplastic and wedged, particularly in the cervical and lumbar regions. The femora and tibiae were short with wide distal metaphyses, undermodeled diaphyses, and coxa vara. The humeri, radii, and ulnae were also short and undermodeled with proximal and distal flare. Chondro-osseous morphology showed short chondrocyte columns, extension of hypertrophic cells into the metaphysis, and overgrowth of perichondral bone. In the resting cartilage there were large chondrocytes containing a homogeneous material staining pink with von Kossa trichrome, gray with toluidine blue, and black with silver methenamine. The cortical bone was lacking and the trabecular bone was hypercellular, thick, and coarse. Ultrastructurally, the resting zone chondrocytes were large and round with condensed chromatin and dilated loops of rough endoplasmic reticulum. The radiographic and histopathologic findings in this case are unique and differ from those seen in other reported lethal osteosclerotic skeletal dysplasias.

Schwartz-Jampel syndrome type 2 and Stüve-Wiedemann syndrome: a case for "lumping"

Recent studies demonstrated the existence of a genetically distinct, usually lethal form of the Schwartz-Jampel syndrome (SJS) of myotonia and skeletal dysplasia, which we called SJS type 2. This disorder is reminiscent of another rare condition, the Stüve-Wiedemann syndrome (SWS), which comprises campomelia at birth with skeletal dysplasia, contractures, and early death. To test for possible nosologic identity between these disorders, we reviewed the literature and obtained a follow-up of the only two surviving patients, one with SJS type 2 at age 10 years and another with SWS at age 7 years. Patients reported as having either neonatal SJS or SWS presented a combination of a severe, prenatal-onset neuromuscular disorder (with congenital joint contractures, respiratory and feeding difficulties, tendency to hyperthermia, and frequent death in infancy) with a distinct campomelic-metaphyseal skeletal dysplasia. The similarity of the clinical and radiographic findings is so extensive that these disorders appear to be a single entity. The follow-up observation of an identical and unique pattern of progressive bone dysplasia in the two patients (one with SJS type 2, one with SWS) surviving beyond infancy adds to the evidence in favor of identity. The hypothesis that SWS and SJS type 2 are the same disorder should be testable by molecular methods.

A lethal skeletal dysplasia with features of chondrodysplasia punctata and osteogenesis imperfecta: an example of Astley-Kendall dysplasia. Further delineation of a rare genetic disorder

An unusual osteochondrodysplasia presenting with lethal neonatal short limbed dwarfism, defective ossification, and punctate calcification within cartilage is presented. The features resemble four cases previously described with Astley-Kendall dysplasia.

Atelosteogenesis type 2

Atelosteogenesis type 2 (AO2) (MIM 256050) is a neonatally lethal chondrodysplasia characterised by severe limb shortening and deficient ossification of parts of the skeleton. Other features include facial dysmorphism, cleft palate, talipes, and abducted thumbs and toes. Phenotypic overlap with non-lethal diastrophic dysplasia (DTD) suggested a common aetiology and it has recently been confirmed that both syndromes result from mutations in the DTDST (diastrophic dysplasia sulphate transporter) gene.

Undersulfation of cartilage proteoglycans ex vivo and increased contribution of amino acid sulfur to sulfation in vitro in McAlister dysplasia/atelosteogenesis type 2

Mutations in the diastrophic dysplasia sulfate transporter gene cause a family of chondrodysplasias including, in order of increasing severity, diastrophic dysplasia, atelosteogenesis type 2 and achondrogenesis type 1B. McAlister dysplasia is a lethal chondrodysplasia considered on the basis of minor radiographic features to be a disorder different from atelosteogenesis type 2. Here, we demonstrate that McAlister dysplasia arises from mutations in the diastrophic dysplasia sulfate transporter gene and that this disorder essentially coincides on molecular and biochemical grounds with atelosteogenesis type 2. The fetus affected by McAlister dysplasia we have studied is a compound heterozygote for mutations leading to R279W and N425D substitutions in the diastrophic dysplasia sulfate transporter. Proteoglycan sulfation was studied in epiphyseal cartilage and in chondrocyte cultures of the patient by high performance liquid chromatography of chondrotinase digested proteoglycans; a high amount of non-sulfated disaccharide was observed as a consequence of the alteration of the transporter function caused by the mutations. However, sulfated disaccharides were detectable even if in low amounts, both in cultured cells and tissue. Functional impairment of the sulfate transporter was demonstrated in vitro by reduced incorporation of [35S]sulfate relative to [3H]glucosamine in proteoglycans synthesized by chondrocytes and by sulfate-uptake assays in fibroblasts. Parallel in vitro studies in a patient with achondrogenesis 1B indicated that the severity of the clinical phenotype seems to be correlated to the residual activity of the sulfate transporter. The capacity of fibroblasts to use cysteine as an alternative source of sulfate was evaluated by double-labeling experiments. Relative incorporation of [35S]cysteine-derived sulfate in the glycosaminoglycan chains was increased in the patient's cells, indicating that, in vitro, the catabolism of sulfur-containing amino acids can partially compensate for intracellular sulfate deficiency. Residual sulfation observed in proteoglycans extracted from cartilage suggests that this mechanism may be operating also in vivo.

Murine models of human genetic skeletal disorders

Genetic and molecular biological studies have recently resulted in the identification of gene mutations responsible for a large number of human osteochondrodysplasias, skeletal disorders associated with abnormalities of cartilage and/or bone development and growth. Mouse strains carrying mutations in homologous genes are useful, not only because they provide sources of abnormal tissue, but also because specific hypotheses concerning pathogenetic mechanisms can be readily tested. Many of the strains with abnormalities in cartilage and bone have been studied by morphological and biochemical methods for years without successful identification of the genes involved, but recent use of linkage mapping, followed by positional candidate gene cloning, has greatly improved the situation. In a number of instances, the mutations are now known. This is also true for the three "classical" mouse mutants chondrodysplasia (cho), disproportionate micromelia (Dmm) and cartilage matrix deficiency (cmd). In the three strains, mutations in alpha 1(XI) collagen, alpha 1(II) collagen or aggrecan lead to severe defects in the structure and function of cartilage with significant negative effects on longitudinal bone growth.

Opsismodysplasia: a case report

A 6-month-old boy with opsismodysplasia is reported. The purpose of this paper is to draw attention to severe ureteric reflux and incidence of pseudo-obstruction, findings not previously reported in opsismodysplasia. They are most likely the result of an intrinsic neuromuscular defect which also affects the skeletal muscles. Another new feature, not reported in opsismodysplasia, was dilatation of ventricles probably secondary to brain atrophy.

New form of platyspondylic lethal chondrodysplasia

We report on a sporadic case of hitherto unknown lethal skeletal dysplasia. The cardinal clinical manifestations consisted of frontal bossing, cloudy corneae, low nasal ridge, and micrognathia, hypoplastic thorax, and rhizomelic micromelia. Laryngoscopy and neck CT disclosed laryngeal stenosis, and brain CT demonstrated hypoplasia of the corpus callosum. Skeletal survey demonstrated hypoplasia of facial bones and short skull base, extremely severe platyspondyly, hypoplastic ilia, and delayed epiphyseal ossification and rhizomelic shortness of tubular bones. The long bones appeared overtubulated with exaggerated metaphyseal flaring. The humeri were particularly short and bowed. Bowing of the radii and ulnae with subluxation of radial heads presented as a Madelung-like deformity. Unlike the long bones, the short tubular bones were not short and normally modeled. The skeletal changes were superficially similar to those in a group of lethal platyspondylic chondrodysplasias, but were inconsistent with any known subtypes of this group or other lethal skeletal dysplasias.

Achondrogenesis type 1B

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Short rib-polydactyly syndrome in twins: Beemer-Langer type with polydactyly

We present premature female twin fetuses with concordant extremely shortened ribs, short limbs, macrocephaly, median cleft upper lip and facial dysmorphism. Based on radiological criteria and the pattern of associated abnormalities, a lethal short rib-polydactyly syndrome (Beemer-Langer type) was diagnosed. The differential diagnosis of this entity is discussed.

Jeune syndrome with tongue lobulation and preaxial polydactyly, and Jeune syndrome with situs inversus and asplenia: compound heterozygosity Jeune-Mohr and Jeune-Ivemark?

We report on a male infant with internal hydrocephalus, absence of corpus callosum, papillomas and lobulation of the tongue, notches of the alveolar ridges, short ribs, dysplastic pelvis, hypospadias, short limbs with bowed long tubular bones and postaxial polydactyly of hands, and preaxial polydactyly in one foot. Radiologically this case shares manifestations with Jeune syndrome; the tongue lobulation and the preaxial polydactyly are similar to findings in Mohr syndrome, or short-rib polydactyly syndrome (SRPS), type Majewski. In addition, a female newborn presented with manifestations of Jeune and Ivemark syndromes. One explanation for this overlap may be compound heterozygosity for these syndromes.

Radiological and histological variants of thanatophoric dysplasia are associated with common mutations in FGFR-3

We describe two fetuses of the 21st week of gestation that share some macroscopic, radiologic, and histologic findings of thanatophoric dysplasia (TD), but also show distinct differences from the usual subtypes of TD. These differences mainly comprise the lack of facial abnormality, only mild reduction of chondrocyte proliferation and hypertrophy, and the lack of fibrous tissue interposition between cartilage and periosteal bone. Thus, these two cases may represent a distinct variant of thanatophoric dysplasia. The molecular analysis of the FGF-R-3 gene demonstrated in both cases mutations which were not significantly different from those of other cases of TD. Thus, the phenotypic modulation within the subtypes of TD may be influenced by additional and yet unknown factors.

Type II collagenopathies: are there additional family members?

The type II collagenopathies represent a group of chondrodysplasias sharing clinical and radiological manifestations which are expressed as a continuous spectrum of phenotypes, ranging from perinatally lethal to very mild conditions. Their common molecular bases are mutations in the type II collagen gene (COL2A1). We describe one case of lethal platyspondylic dysplasia, Torrance type, and a variant of lethal Kniest dysplasia, neither of which has been reported as a type II collagenopathy. Biochemical studies of cartilage collagens and morphological analysis of cartilage sections suggest that abnormalities of type II collagen structure and biosynthesis are the main pathogenetic factors in both cases. Thus, the phenotypic spectrum of type II collagenopathies might be greater than hitherto suspected.

Short rib-dysplasia group (with/without polydactyly): report of a patient suggesting the existence of a continuous spectrum

We report on a patient with manifestations typical of Mohr syndrome and of the short rib (polydactyly) syndromes (SR(P)S) Majewski, Verma-Naumoff, Beemer, and Jeune. It seems possible that the different types of SR(P) syndromes, rather than being distinct conditions, are part of a large disease spectrum. The frequent overlap between orofaciodigital syndromes and SR(P) syndromes may be interpreted as the outcome of deletions of different size within the same chromosome region.

Histopathology of fetal diastrophic dysplasia

We report on three cases of diastrophic dysplasia in second trimester fetuses and discuss the differential diagnosis and clinical, radiologic, and histopathologic findings. Manifestations of typical diastrophic dysplasia in infants and older patients include abnormal pinnae, scoliosis, and joint contractures; these were absent in the fetuses, in keeping with the tendency for the clinical and radiologic aspects of this disease to become more severe with age. The histopathologic characteristics of the cartilage appear to be similar in the fetus and older patient, and therefore may be useful in differentiating diastrophic dysplasia from other osteochondrodysplasias in the second trimester.

Prenatal diagnosis of recurrence of short rib-polydactyly syndrome

We describe a nonconsanguineous couple whose 3 successive pregnancies, including one pair of twins, led to the birth of 4 infants with short rib-polydactyly syndrome (SRPS). Flat face, hypoplastic thorax, short limbs and ribs, polydactyly, absence of penis, and death after birth were noted in the first affected male baby. The affected female twins were detected prenatally by ultrasonography and had the same characteristics, but milder than the previous one. Serial measurements of the thoracic circumference and the 4 limbs were obtained by ultrasound, and showed progressively decreased ratio of thoracic to abdominal circumference and shortness of the limbs. The last male baby also had a similar but variable expression in prenatal ultrasonography.

Human COL2A1-directed SV40 T antigen expression in transgenic and chimeric mice results in abnormal skeletal development

The ability of SV40 T antigen to cause abnormalities in cartilage development in transgenic mice and chimeras has been tested. The cis-regulatory elements of the COL2A1 gene were used to target expression of SV40 T antigen to differentiating chondrocytes in transgenic mice and chimeras derived from embryonal stem (ES) cells bearing the same transgene. The major phenotypic consequences of transgenic (pAL21) expression are malformed skeleton, disproportionate dwarfism, and perinatal/neonatal death. Expression of T antigen was tissue specific and in the main characteristic of the mouse alpha 1(II) collagen gene. Chondrocyte densities and levels of alpha 1(II) collagen mRNAs were reduced in the transgenic mice. Islands of cells which express cartilage characteristic genes such as type IIB procollagen, long form alpha 1(IX) collagen, alpha 2(XI) collagen, and aggrecan were found in the articular and growth cartilages of pAL21 chimeric fetuses and neonates. But these cells, which were expressing T antigen, were not properly organized into columns of proliferating chondrocytes. Levels of alpha 1(II) collagen mRNA were reduced in these chondrocytes. In addition, these cells did not express type X collagen, a marker for hypertrophic chondrocytes. The skeletal abnormality in pAL21 mice may therefore be due to a retardation of chondrocyte maturation or an impaired ability of chondrocytes to complete terminal differentiation and an associated paucity of some cartilage matrix components.

The chondrodystrophy, nanomelia: biosynthesis and processing of the defective aggrecan precursor

The lethal chicken mutation nanomelia leads to severe skeletal defects because of a deficiency of aggrecan, which is the largest aggregating chondroitin sulphate proteoglycan of cartilage. In previous work, we have demonstrated that nanomelic chondrocytes produce a truncated aggrecan precursor that fails to be secreted, and is apparently arrested in the endoplasmic reticulum (ER). In this study, we investigated the biosynthesis and extent of processing of the abnormal aggrecan precursor. The truncated precursor was translated directly in cell-free reactions, indicating that it does not arise post-translationally. Further studies addressed the processing capabilities of the defective precursor. We found that the mutant precursor was modified by N-linked, mannose-rich oligosaccharides and by the addition of xylose, but was not further processed; this is consistent with the conclusion that it moves no further along the secretory pathway than the ER. Using brefeldin A we demonstrated that the defective precursor can function as a substrate for Golgi-mediated glycosaminoglycan chains, but does not do so in the nanomelic chondrocyte because it fails to be translocated to the appropriate membrane compartment. These studies illustrate how combined cell biological/biochemical and molecular investigations may contribute to our understanding of the biological consequences and molecular basis of genetic diseases, particularly those involving errors in large, highly modified molecules such as proteoglycans.