Biomedical subjects

W R Wilcox

Publications and source records attributed to W R Wilcox.

At least 37 records · Page 2Linked to original sources

PubMed1999

A novel skeletal dysplasia with developmental delay and acanthosis nigricans is caused by a Lys650Met mutation in the fibroblast growth factor receptor 3 gene.

We have identified a novel fibroblast growth factor receptor 3 (FGFR3) missense mutation in four unrelated individuals with skeletal dysplasia that approaches the severity observed in thanatophoric dysplasia type I (TD1). However, three of the four individuals developed extensive areas of acanthosis nigricans beginning in early childhood, suffer from severe neurological impairments, and have survived past infancy without prolonged life-support measures. The FGFR3 mutation (A1949T: Lys650Met) occurs at the nucleotide adjacent to the TD type II (TD2) mutation (A1948G: Lys650Glu) and results in a different amino acid substitution at a highly conserved codon in the kinase domain activation loop. Transient transfection studies with FGFR3 mutant constructs show that the Lys650Met mutation causes a dramatic increase in constitutive receptor kinase activity, approximately three times greater than that observed with the Lys650Glu mutation. We refer to the phenotype caused by the Lys650Met mutation as "severe achondroplasia with developmental delay and acanthosis nigricans" (SADDAN) because it differs significantly from the phenotypes of other known FGFR3 mutations.

Acanthosis Nigricans↗

PubMed1999

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.

Achondroplasia↗

PubMed1998

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.

Abortion, Induced↗

PubMed1998

Thanatophoric dysplasia type I with syndactyly.

We report on a case of thanatophoric dysplasia type 1 (TD1) due to a Tyr373Cys mutation in the fibroblast growth factor receptor 3 (FGFR3) gene with soft tissue syndactyly of the fingers and toes. Syndactyly has not been previously described in TD or other conditions with FGFR3 mutations, but occurs in several craniosynostosis syndromes due to mutations in FGFR2. We conclude that mutations in FGFR3 may also be associated with developmental abnormalities due to interference with programmed cell death.

Cysteine↗

PubMed1998

Radiographic and morphologic findings in a previously undescribed type of mesomelic dysplasia resembling atelosteogenesis type II.

The mesomelic chondrodysplasias are a heterogeneous group of dwarfing disorders characterized by shortness of the middle segments of limbs. We report on a 25-week fetus with disproportionate shortness of limbs with an apparently distinct form of mesomelic dysplasia. Radiographic findings at necropsy included ulnar deviation of hands, talipes equinovarus, distal tapering of the humeri, and hypoplastic fibulae, radii, and ulnae. Chondro-osseous morphology showed mild shortness of the physeal columns, overgrowth of perichondral bone, peripheral ingrowth of mesenchymal cells into the physis, and numerous areas of fibrillar degeneration with rings of collagen surrounding the chondrocytes. Ultrastructural findings included a degenerated territorial matrix, pericellular halos of collagen, and dilated loops of rough endoplasmic reticulum in chondrocytes. The radiographic appearance of the long bones is distinct from that of previously described mesomelic dysplasias. The chondro-osseous morphologic findings and the distal tapering of the humerus are somewhat reminiscent of atelosteogenesis type II, but the pattern of matrix degeneration and the presence of inclusion bodies in the chondrocytes distinguish it from disorders of sulfate transport.

Aggrecans↗

PubMed1998

Physiological and pathological secretion of cartilage oligomeric matrix protein by cells in culture.

Abnormalities in cartilage oligomeric matrix protein (COMP), a pentameric structural protein of the cartilage extracellular matrix, have been identified in pseudoachondroplasia and multiple epiphyseal dysplasia, two human autosomal dominant osteochondrodysplasias. However, the function of the protein remains unknown. With the goal of establishing a model to study the mechanisms by which COMP mutations cause disease, we have analyzed synthesis and secretion of COMP in cultured chondrocytes, tendon, and ligament cells. Pentameric protein detected inside of control cells suggested that pentamerization is an intracellular process. Patient cells expressed mutant and normal RNA and secreted COMP at levels similar to controls, suggesting that abnormal pentamers are likely to be found in the extracellular matrix. Inclusions within patient cartilage stained with anti-COMP antibodies, and cultured cells presented similar inclusions, indicating that presumably abnormal COMP pentamers are less efficiently secreted than normal molecules. We conclude that the COMP disorders are likely to result from a combination of a decreased amount of COMP in the matrix and a dominant negative effect due to the presence of abnormal pentamers in cartilage.

Base Sequence↗

PubMed1998

Incorporation of structurally defective type II collagen into cartilage matrix in kniest chondrodysplasia.

Kniest dysplasia, a human chondrodysplasia that severely affects skeletal growth, is caused by mutations in the type II collagen gene, COL2A1. We report here on abnormal type II collagen in the cartilage from a lethal Kniest dysplasia case and identify a novel exon-skipping mutation. Screening of cyanogen bromide (CB) peptides from the cartilage samples by SDS-PAGE indicated an abnormality in peptide alpha1(II)CB11. Further peptide mapping and N-terminal sequence analysis showed a 15-amino-acid deletion encoded by exon 15 in about 25% of the alpha1(II) chains in the cartilage. The mutation responsible for exon skipping was found by sequencing amplified genomic DNA. The baby was heterozygous for a G to A transition at the first position of the splice donor of intron 15. Pepsin-solubilized type II collagen from the cartilage matrix contained both normal alpha1(II) and shortened chains expressed from the mutant allele. Trypsin cleaved the native molecules below 37 degrees C selectively at a site within the exon 15-encoded domain of the normal alpha1(II) chains. This is best explained by the coassembly of normal and truncated alpha1(II) chains into heterotrimers in which the triple helix is normally folded in both directions from the deletion site but the latter presents a region of local disruption. The findings support an emerging pattern of COL2A1 mutations that can cause Kniest dysplasia. Short deletions (single or partial exon) clustered in one region of the alpha1(II) chain are favored, resulting in abnormal heterotrimeric molecules that become a significant component of the cartilage extracellular matrix.

Amino Acid Sequence↗

PubMed1998

Molecular, radiologic, and histopathologic correlations in thanatophoric dysplasia.

Various mutations in the fibroblast growth factor receptor 3 (FGFR3) gene have recently been reported in thanatophoric dysplasia (TD). We examined the clinical, radiographic, and histologic findings in 91 cases from the International Skeletal Dysplasia Registry and correlated them with the specific FGFR3 mutation. Every case of TD examined had an identifiable FGFR3 mutation. Radiographically, all of the cases with the Lys650Glu substitution demonstrated straight femora with craniosynostosis, and frequently a cloverleaf skull (CS) was demonstrated. In all other cases, the femora were curved, and CS was infrequently present but was occasionally as severe as TD with the Lys650Glu substitution. Histopathologically, all of the cases shared similar abnormalities, but cases with the Lys650Glu substitution had better preservation of the growth plate. Cases with the Tyr373Cys substitution tended to have more severe radiographic manifestations than the Arg248Cys cases, but there was overlap in the phenotypic spectrum between them. One common classification of TD distinguishes affected infants based on the presence or absence of CS. In contrast, and as originally proposed by Langer et al. [1987: Am J Med Genet 3: 167-179], our data suggest that TD can be divided into at least two groups (TD1 and TD2) based on the presence of straight or curved femora. The variable presence of CS and severity of the radiologic and histologic findings in the other substitutions may be due to other genetic, environmental, or stochastic factors.

Chondrocytes↗

PubMed1998

Pacman dysplasia: report of two affected sibs.

We report on two sib fetuses with radiological and morphological findings similar to those of the recently described lethal skeletal dysplasia termed Pacman dysplasia (McKusick, 167220, Am J Med Genet 1993, 45:558-561). The first fetus, a male, was electively terminated after a routine ultrasound study at 20 weeks showed short-limb dwarfism. The second fetus, a female sib, was also electively terminated after similar, abnormal ultrasound findings were noted at 16 weeks of gestation. Similar to Pacman dysplasia, the radiographic appearance was characterized by under-mineralized bone, stippling, rhizomelic and mesomelic shortness, platyspondyly, and a short, broad pelvis. The metaphyses were dense, but the diaphyseal cortices were thin with undermodeled long bones, and there was a deficient trabecular pattern suggesting marrow replacement. Chondro-osseous structure was characterized by deficient trabecular bone formation, a fibrous marrow, and numerous, large, multinucleated osteoclasts lining the endosteal surfaces of the metaphyseal bone. The occurrence of this dysplasia in sibs of differing sex suggests autosomal recessive inheritance.

Female↗

PubMed1998

Structurally abnormal type II collagen in a severe form of Kniest dysplasia caused by an exon 24 skipping mutation.

Type II collagen mutations have been identified in a phenotypic continuum of chondrodysplasias that range widely in clinical severity. They include achondrogenesis type II, hypochondrogenesis, spondyloepiphyseal dysplasia congenita, spondyloepimetaphyseal dysplasia, Kniest dysplasia, and Stickler syndrome. We report here results that define the underlying genetic defect and consequent altered structure of assembled type II collagen in a neonatal lethal form of Kniest dysplasia. Electrophoresis of a cyanogen bromide (CNBr) (CB) digest of sternal cartilage revealed an alpha1(II)CB11 peptide doublet and a slightly retarded mobility for all major CB peptides, which implied post-translational overmodification. Further peptide mapping and sequence analysis of CB11 revealed equal amounts of a normal alpha1(II) sequence and a chain lacking the 18 residues (361-378 of the triple helical domain) corresponding to exon 24. Sequence analysis of an amplified genomic DNA fragment identified a G to A transition in the +5 position of the splice donor consensus sequence of intron 24 in one allele. Cartilage matrix analysis showed that the short alpha1(II) chain was present in collagen molecules that had become cross-linked into fibrils. Trypsin digestion of the pepsin-extracted native type II collagen selectively cleaved the normal length alpha1(II) chains within the exon 24 domain. These findings support a hypothesis that normal and short alpha-chains had combined to form heterotrimeric molecules in which the chains were in register in both directions from the deletion site, accommodated effectively by a loop out of the normal chain exon 24 domain. Such an accommodation, with potential overall shortening of the helical domain and hence misalignment of intermolecular relationships within fibrils, offers a common molecular mechanism by which a group of different mutations might act to produce the Kniest phenotype.

Amino Acid Sequence↗

PubMed1998

Gracile bone dysplasia.

Gracile bones are a frequent abnormality associated with fetal hypokinesia of any cause. With the exception of thin, undermineralized bones, the chondro-osseous structure is usually normal in these cases. We present a lethal skeletal dysplasia comprising minor anomalies, central nervous system abnormalities, gracile long bones, and abnormal chondro-osseous morphology. In addition to a short, disordered growth plate, the chondrocytes contained dilated loops of rough endoplasmic reticulum, suggesting an abnormality of an extracellular matrix protein. This protein appears to have effects on chondro-osseous and on facial and central nervous system development. We suggest the term "gracile bone dysplasia" to describe this disorder.

Bone Diseases, Developmental↗

PubMed1998

Extra pelvic ossification centers in thanatophoric dysplasia and platyspondylic lethal skeletal dysplasia-San Diego type.

The platyspondylic lethal skeletal dysplasias (PLSD) are a group of heterogeneous disorders including thanatophoric dysplasia (TD) and the TD variants (San Diego, Torrance, and Luton types). TD is the most common form and has been divided into two subtypes (TD1 and TD2) based on clinical and radiologic criteria and analysis of mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. The variants are distinguished from TD by characteristic radiographic and chondro-osseous morphologic features. We have recently identified FGFR3 mutations in PLSD-San Diego type (PLSD-SD) which are identical to those found in TD1, but the known TD FGFR3 mutations were not found in the other PLSD variants. After reviewing radiographs from 32 cases of PLSD-SD and 47 cases of TD with gestational ages under 24 weeks, we noted novel accessory ossification centers in the ischia of 18 cases of PLSD-SD and 44 of TD, and the ilia in 18 cases of PLSD-SD and 20 of TD. Only three cases of TD and five cases of PLSD-SD did not have extra pelvic ossification centers. At a gestational age greater than 24 weeks, the extra centers are fused with the main bone. The radiographic appearance and chondro-osseous morphology of cases with and without accessory pelvic ossification centers were otherwise indistinguishable. Morphologically, the accessory pelvic ossification centers resulted from membranous ossification. Extra pelvic ossifications are a common radiographic finding in TD and PLSD-SD.

Abnormalities, Multiple↗

PubMed1998

Cumming syndrome: report of two additional cases.

We present two unrelated cases with a similar pattern of multiple congenital anomalies including limb shortening, long bone angulation, and cervical lymphocele. We believe these cases to represent additional examples of a syndrome first described by Cumming et al. (1986), and by Urioste et al. (1991) and Ming et al. (1997).

Abnormalities, Multiple↗

PubMed1998

Proteoglycan sulfation in cartilage and cell cultures from patients with sulfate transporter chondrodysplasias: relationship to clinical severity and indications on the role of intracellular sulfate production.

Mutations in the diastrophic dysplasia sulfate transporter (DTDST) gene have been associated with a family of chondrodysplasias that includes diastrophic dysplasia (DTD), atelosteogenesis type 2 (AO2) and the lethal condition achondrogenesis type 1B (ACG1B). There is a correlation between the nature of the mutations and the clinical phenotype, but our understanding of the pathophysiology of the disorder, which involves defective sulfation of cartilage proteoglycans, is far from complete. To evaluate the degree of proteoglycan undersulfation in vivo, we have extracted chondroitin sulfate proteoglycans from cartilage of twelve patients with sulfate transporter chondrodysplasias and analyzed their disaccharide composition by HPLC after digestion with chondroitinase ABC. The amount of non-sulfated disaccharide was elevated in patients' samples (controls, 5.5%+/-2.8 (n=10); patients, 11% to 77%), the highest amount being present in ACG1B patients, indicating that undersulfation of chondroitin sulfate proteoglycans occurs in cartilage in vivo and is correlated with the clinical severity. To investigate further the biochemical mechanisms responsible for the translation of genotype to phenotype, we have studied fibroblast cultures of patients with DTD, AO2 and ACG1B, and controls, by double-labelling with [35S]sulfate and [3H]glucosamine. The incorporation of extracellular sulfate, estimated by the 35S/3H ratio in proteoglycans, was reduced in all patients' cells, with ACG1B cells showing the lowest values. However, disaccharide analysis of chondroitin sulfate proteoglycans showed that these were normally sul fated or only moderately undersulfated; marked undersulfation was observed only after addition of the artificial glycosaminoglycan-chain initiator, beta-D-xyloside, to the culture medium. These results suggest that, while utilization of extracellular sulfate is impaired, fibroblasts can replenish their intracellular sulfate pool by oxidizing sulfur-containing compounds (such as cysteine) and thus partially rescue PG sulfation under basal conditions. This rescue pathway becomes insufficient when GAG synthesis rate is stimulated by beta-D-xyloside. These findings may explain why phenotypic consequences of DTDST mutations are restricted to cartilage, a tissue with high GAG synthesis rate and poor vascular supply, and imply that pharmacological therapy aimed at restoring the intracellular sulfate pool might improve PG sulfation in DTD and related disorders.

Anion Transport Proteins↗

PubMed1998

Diverse mutations in the gene for cartilage oligomeric matrix protein in the pseudoachondroplasia-multiple epiphyseal dysplasia disease spectrum.

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are autosomal dominant osteochondrodysplasias that result in mild to severe short-limb dwarfism and early-onset osteoarthrosis. PSACH and some forms of MED result from mutations in the gene for cartilage oligomeric matrix protein (COMP; OMIM 600310 [http://www3.ncbi.nlm. nih.gov:80/htbin-post/Omim/dispmim?600310]). We report the identification of COMP mutations in an additional 14 families with PSACH or MED phenotypes. Mutations predicted to result in single-amino acid deletions or substitutions, all in the region of the COMP gene encoding the calmodulin-like repeat elements, were identified in patients with moderate to severe PSACH. We also identified within this domain a missense mutation that produced MED Fairbank. In two families, one with mild PSACH and the second with a form of MED, we identified different substitutions for a residue in the carboxyl-terminal globular region of COMP. Both the clinical presentations of these two families and the identification of COMP-gene mutations provide evidence of phenotypic overlap between PSACH and MED. These data also reveal a role for the carboxyl-terminal domain in the structure and/or function of COMP.

Achondroplasia↗

PubMed1998

Lys650Met substitution in the tyrosine kinase domain of the fibroblast growth factor receptor gene causes thanatophoric dysplasia Type I. Mutations in brief no. 199. Online.

Thanatophoric dysplasia (TD) is one of the most common neonatal lethal skeletal dysplasias with micromelic shortening of the limbs, relative macrocephaly, flat vertebral bodies and a narrow thorax. TD has been divided into two types, type I (TD1) and II (TD2), based on clinical, radiological, histological, and molecular criteria. We identified a A to T heterozygous base subsitution at position 1949 predicted to cause a Lys650Met substitution in a term infant with TD1. This mutation has been previously described in one case of TD1 and three cases of severe achondroplasia with acanthosis nigricans and mental retardation. Interestingly, all cases with the Lys650Met mutation have the same unusual curvature of the tibia and/or fibula.

Amino Acid Substitution↗

PubMed1997

Clinical, morphological, and biochemical phenotype of a new case of Ehlers-Danlos syndrome type VIIC.

Ehlers-Danlos syndrome (EDS) type VIIC is a newly recognized human disorder which results from failure to remove the amino-terminal propeptide of type I procollagen. Four cases of EDS type VIIC have been reported, and here we describe a fifth case. The propositus was a 1,445 g male infant born at 30 weeks of gestation following premature rupture of membranes. He had wide fontanelles, prominent eyes with swollen eyelids and blue sclerae, anteverted nostrils, micrognathia, umbilical hernia, short stubby fingers, and cutis laxa with hirsutism. At age 3 months, during the repair of the umbilical hernia, he was noted to have unusual skin fragility. Examination of skin by scanning electron microscopy showed frayed collagen fibrils, and transmission electron microscopy showed the hieroglyphic collagen fibril morphology characteristic of the disorder. As reported in other cases, cultured fibroblasts synthesized type I procollagen that was very poorly processed at the amino-terminal propeptide cleavage site. the 5 known cases of human EDS type VIIC characterize a distinct clinical phenotype, making this condition recognizable at birth before manifestation of severe skin fragility. The diagnosis can be confirmed by biochemical studies of type I procollagen synthesis and by electron microscopic examination of skin.

Adolescent↗

PubMed1997

Spondylo-mesomelic-acrodysplasia with joint dislocations and severe combined immunodeficiency: a newly recognised immuno-osseous dysplasia.

A newborn girl is described with an association of spondylo-acrodysplasia, mild short limbed dwarfism without significant metaphyseal changes, joint dislocations, and severe immune system dysfunction. This association is distinct from other known immuno-osseous dysplasias, including Schimke dysplasia, ADA deficiency with osseous changes, and Omenn phenotype with short limbed dwarfism.

Female↗