The phenotypic spectrum in patients with arginine to cysteine mutations in the COL2A1 gene.

BACKGROUND: The majority of COL2A1 missense mutations are substitutions of obligatory glycine residues in the triple helical domain. Only a few non-glycine missense mutations have been reported and among these, the arginine to cysteine substitutions predominate. OBJECTIVE: To investigate in more detail the phenotype resulting from arginine to cysteine mutations in the COL2A1 gene. METHODS: The clinical and radiographic phenotype of all patients in whom an arginine to cysteine mutation in the COL2A1 gene was identified in our laboratory, was studied and correlated with the abnormal genotype. The COL2A1 genotyping involved DHPLC analysis with subsequent sequencing of the abnormal fragments. RESULTS: Six different mutations (R75C, R365C, R519C, R704C, R789C, R1076C) were found in 11 unrelated probands. Each mutation resulted in a rather constant and site-specific phenotype, but a perinatally lethal disorder was never observed. Spondyloarthropathy with normal stature and no ocular involvement were features of patients with the R75C, R519C, or R1076C mutation. Short third and/or fourth toes was a distinguishing feature of the R75C mutation and brachydactyly with enlarged finger joints a key feature of the R1076C substitution. Stickler dysplasia with brachydactyly was observed in patients with the R704C mutation. The R365C and R789C mutations resulted in classic Stickler dysplasia and spondyloepiphyseal dysplasia congenita (SEDC), respectively. CONCLUSIONS: Arginine to cysteine mutations are rather infrequent COL2A1 mutations which cause a spectrum of phenotypes including classic SEDC and Stickler dysplasia, but also some unusual entities that have not yet been recognised and described as type II collagenopathies.

Dentinogenesis imperfecta associated with short stature, hearing loss and mental retardation: a new syndrome with autosomal recessive inheritance?

The follow-up history and oral findings in two brothers from consanguineous parents suggest that the association of dentinogenesis imperfecta (DI), delayed tooth eruption, mild mental retardation, proportionate short stature, sensorineural hearing loss and dysmorphic facies may represent a new syndrome with autosomal recessive inheritance. Histological examination of the dentin matrix of a permanent molar from one of the siblings reveals morphological similarities with defective dentinogenesis as presenting in patients affected with Osteogenesis Imperfecta (OI), a condition caused by deficiency of type I collagen. A number of radiographic and histological characteristics, however, are inconsistent with classical features of DI. These findings suggest that DI may imply greater genetical heterogeneity than currently assumed.

The diagnosis of skeletal dysplasias: a multidisciplinary approach.

Skeletal dysplasias are heritable connective tissue disorders affecting skeletal morphogenesis and development. They represent a heterogeneous group of genetic disorders with more than 200 different entities being delineated to date. Because of this diversity, the diagnosis of a skeletal dysplasia is usually based on a combination of clinical, radiographic, morphologic, and, in some instances, biochemical and molecular studies. Tremendous advances have been made in the elucidation of the genetic defect of several of these conditions over the past 10 years. This progress has provided us with more insights into the genes controlling normal skeletal development. It also has opened new diagnostic perspectives. For several disorders, identification of the causal gene allows us now to confirm with a molecular test the diagnosis postulated on the basis of clinical, radiographic and/or morphologic studies. It also enables us to establish the diagnosis early in pregnancy. An accurate diagnosis is not only important for proper management of the affected individual but also the cornerstone for adequate genetic counseling.

Clinical and radiographic features of multiple epiphyseal dysplasia not linked to the COMP or type IX collagen genes.

Multiple epiphyseal dysplasia (MED) is a mild chondrodysplasia affecting the structural integrity of cartilage and causing early-onset osteoarthrosis in adulthood. The condition is genetically heterogeneous. Mutations in the COMP gene and in two genes (COL9A2; COL9A3), coding respectively for the alpha2(IX) and alpha3(IX) chains of type IX collagen, can cause the autosomal dominant forms of MED. Mutations in the DTDST gene have recently been identified in a recessive form of MED. However, for the majority of MED cases, the genetic defect still remains undetermined. We report a three-generation family with an autosomal dominant form of MED, characterised by normal stature, joint pain in childhood and early-onset osteoarthrosis, affecting mainly the hips and knees. Based on discordant inheritance among affected individuals linkage of the phenotype to the COMP, COL9A1, COL9A2, COL9A3 genes was excluded. Our study provides evidence that at least another locus, distinct from COL9A1, is involved in autosomal dominant MED.

Mutations in the region encoding the von Willebrand factor A domain of matrilin-3 are associated with multiple epiphyseal dysplasia.

Multiple epiphyseal dysplasia (MED) is a relatively mild and clinically variable osteochondrodysplasia, primarily characterized by delayed and irregular ossification of the epiphyses and early-onset osteoarthritis. Mutations in the genes encoding cartilage oligomeric matrix protein (COMP) and type IX collagen (COL9A2 and COL9A3) have previously been shown to cause different forms of MED (refs. 4-13). These dominant forms of MED (EDM1-3) are caused by mutations in the genes encoding structural proteins of the cartilage extracellular matrix (ECM); these proteins interact with high affinity in vitro. A recessive form of MED (EDM4) has also been reported; it is caused by a mutation in the diastrophic dysplasia sulfate transporter gene (SLC26A). A genomewide screen of family with autosomal-dominant MED not linked to the EDM1-3 genes provides significant genetic evidence for a MED locus on the short arm of chromosome 2 (2p24-p23), and a search for candidate genes identified MATN3 (ref. 18), encoding matrilin-3, within the critical region. Matrilin-3 is an oligomeric protein that is present in the cartilage ECM. We have identified two different missense mutations in the exon encoding the von Willebrand factor A (vWFA) domain of matrilin-3 in two unrelated families with MED (EDM5). These are the first mutations to be identified in any of the genes encoding the matrilin family of proteins and confirm a role for matrilin-3 in the development and homeostasis of cartilage and bone.

Imaging studies in the diagnostic workup of neonatal nasal obstruction.

Twelve neonates presenting with nasal obstruction after birth were evaluated by imaging studies for diagnostic reasons. Four groups were recognized: Group I: choanal atresia (n = 5) and choanal stenosis (n = 1); Group II: congenital nasal pyriform aperture stenosis (CNPAS) (n = 3) and holoprosencephaly (n = 1); Group III: nasolacrimal duct mucocele (n = 1); Group IV: nasal hypoplasia (n = 1). Associated anomalies were found in eight patients. Four patients with choanal atresia showed manifestations of the CHARGE (coloboma, congenital heart defect, atretic choanae, retarded physical and neuromotor development associated with central nervous system anomalies, genital hypoplasia, and ear anomaly and/or deafness) association. In the fifth patient with choanal atresia, the diagnosis of amnion disruption sequence was made. One patient with CNPAS had a solitary maxillary central incisor (SMCI), a mild form of holoprosencephaly. Besides proboscis and synophthalmos, SMCI was also present in the holoprosencephaly case. The patient with severe nasal hypoplasia had warfarin embryopathy. This review emphasizes the need for performing imaging studies in the diagnostic workup of neonates born with nasal obstruction.

Unilateral semicircular canal aplasia in Goldenhar's syndrome.

A patient with Goldenhar's syndrome (oculoauriculovertebral dysplasia) and unilateral aplasia of all semicircular canals is presented. This is the first report of such a finding and may support the hypothesis that Goldenhar's syndrome and the CHARGE association have a common pathogenetic mechanism.

Report of five novel and one recurrent COL2A1 mutations with analysis of genotype-phenotype correlation in patients with a lethal type II collagen disorder.

Achondrogenesis II-hypochondrogenesis and severe spondyloepiphyseal dysplasia congenita (SEDC) are lethal forms of dwarfism caused by dominant mutations in the type II collagen gene (COL2A1). To identify the underlying defect in seven cases with this group of conditions, we used the combined strategy of cartilage protein analysis and COL2A1 mutation analysis. Overmodified type II collagen and the presence of type I collagen was found in the cartilage matrix of all seven cases. Five patients were heterozygous for a nucleotide change that predicted a glycine substitution in the triple helical domain (G313S, G517V, G571A, G910C, G943S). In all five cases, analysis of cartilage type II collagen suggested incorporation of the abnormal alpha1(II) chain in the extracellular collagen trimers. The G943S mutation has been reported previously in another unrelated patient with a strikingly similar phenotype, illustrating the possible specific effect of the mutation. The radiographically less severely affected patient was heterozygous for a 4 bp deletion in the splice donor site of intron 35, likely to result in aberrant splicing. One case was shown to be heterozygous for a single nucleotide change predicted to result in a T1191N substitution in the carboxy-propeptide of the proalpha1(II) collagen chain. Study of the clinical, radiographic, and morphological features of the seven cases supports evidence for a phenotypic continuum between achondrogenesis II-hypochondrogenesis and lethal SEDC and suggests a relationship between the amount of type I collagen in the cartilage and the severity of the phenotype.

Identification of novel pro-alpha2(IX) collagen gene mutations in two families with distinctive oligo-epiphyseal forms of multiple epiphyseal dysplasia.

Multiple epiphyseal dysplasia (MED) is a genetically heterogeneous disorder with marked clinical and radiographic variability. Traditionally, the mild "Ribbing" and severe "Fairbank" types have been used to define a broad phenotypic spectrum. Mutations in the gene encoding cartilage oligomeric-matrix protein have been shown to result in several types of MED, whereas mutations in the gene encoding the alpha2 chain of type IX collagen (COL9A2) have so far been found only in two families with the Fairbank type of MED. Type IX collagen is a heterotrimer of pro-alpha chains derived from three distinct genes-COL9A1, COL9A2, and COL9A3. In this article, we describe two families with distinctive oligo-epiphyseal forms of MED, which are heterozygous for different mutations in the COL9A2 exon 3/intron 3 splice-donor site. Both of these mutations result in the skipping of exon 3 from COL9A2 mRNA, but the position of the mutation in the splice-donor site determines the stability of the mRNA produced from the mutant COL9A2 allele.

Exon 10b of the NF1 gene represents a mutational hotspot and harbors a recurrent missense mutation Y489C associated with aberrant splicing.

PURPOSE: To analyze the spectrum and frequency of NF1 mutations in exon 10b. METHODS: Mutation and sequence analysis was performed at the DNA and cDNA level. RESULTS: We identified nine exon 10b mutations in 232 unrelated patients. Some mutations were recurrent (Y489C and L508P), others were unique (1465-1466insC and IVS10b+2delTAAG). Surprisingly, at the RNA level, Y489C causes skipping of the last 62 nucleotides of exon 10b. Another recurrent mutation, L508P, is undetectable by the Protein Truncation Test. CONCLUSION: As exon 10b shows the highest mutation rate yet found in any of the 60 NF1 exons, it should be implemented with priority in mutation analysis.

Chondrodysplasia punctata with multiple congenital anomalies: a new syndrome?

We report a male neonate with craniofacial dysmorphic features, multiple congenital anomalies and an unusual form of chondrodysplasia punctata. Radiographic examination revealed punctate epiphyses and coronal clefting of the thoracic spine. The hand radiographs showed some similarities to the brachytelephalangic type of chondrodysplasia punctata. However, the disorder did not fit well with any known entity of chondrodysplasia punctata or other condition characterized by punctate epiphyses.

Correlation of linkage data with phenotype in eight families with Stickler syndrome.

The clinical findings of eight families with Stickler syndrome were analyzed and compared with the results of linkage studies using a marker for the type II collagen gene (COL2A1). In six families, there was linkage of the phenotype to COL2A1. The manifestations of the affected individuals were similar to those of the original Stickler syndrome family [Stickler et al., Mayo. Clin. Proc. 40:433-455, 1965] and resembled the phenotype of the previously reported individuals or families with Stickler syndrome in which a dominant mutation in the COL2A1 gene has been identified. Linkage to COL2A1 was excluded in the two remaining families. The most striking difference between these two types of families was the absence of severe myopia and retinal detachment in the two unliked families. In the COL2A1 unlinked families, linkage of the phenotype to genes (COL11A1 and COL11A2) that encode pro alpha chains of type XI collagen, a minor cartilage-specific collagen, was also excluded. Since Stickler syndrome can be produced by mutations in COL2A1, COL11A1, and COL11A2, our data suggest that there is at least a fourth locus for Stickler syndrome.

Syndrome of coronal craniosynostosis with brachydactyly and carpal/tarsal coalition due to Pro250Arg mutation in FGFR3 gene.

Recently, a unique Pro250Arg point mutation in fibroblast growth factor receptor 3 (FGFR3) was reported in 61 individuals with coronal craniosynostosis from 20 unrelated families [Muenke et al. (1997): Am J Hum Genet 60:555-564]. The discovery of this apparently common mutation has resulted in the definition of a recognizable syndrome, through analysis of subtle clinical findings in families who were previously thought to have a variety of other craniosynostosis syndromes. Previous diagnoses in some of these families have included Jackson-Weiss, Saethre-Chotzen, and Pfeiffer syndromes, as well as Adelaide-type craniosynostosis and brachydactyly-craniosynostosis syndrome [Adès et al. (1994): Am J Med Genet 51:121-130; von Gernet et al. (1996): Am J Med Genet 63:177-184; Reardon et al. (1997): J Med Genet 34:632-636; Bellus et al. (1996): Nat Genet 14:174-176; Hollaway et al. (1995): Hum Mol Genet 4:681-683; Glass et al. (1994): Clin Dysmorphol 3:215-223]. There appears to be a need to further delineate the phenotype associated with this common mutation in FGFR3. We compare the clinical characteristics of previously reported cases of this unique Pro250Arg mutation with those of two additional families and suggest that this syndrome with a unique mutational basis be designated coronal craniosynostosis with brachydactyly and carpal/tarsal coalition due to Pro250Arg mutation in FGFR3 gene, to emphasize the distinctive findings which may be present even in the absence of coronal craniosynostosis.

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.

The scapula as a window to the diagnosis of skeletal dysplasias.

Evaluation of the scapula can be useful in the diagnosis of skeletal dysplasias and helpful for the classification and delineation of new entities. A review of 2100 computerized cases of skeletal dysplasias in the International Skeletal Dysplasia Registry was performed. We found that the Luton type of platyspondylic lethal skeletal dysplasia differed radiographically from the San Diego type and Torrance type by the presence of two spikes at the inferior angle of the scapula. Hypoplasia of the body of the scapula, which is characteristic for campomelic dysplasia but not for kyphomelic dysplasia, is also present in Antley-Bixler syndrome. Radiographic and clinical similarities between campomelic dysplasia and Antley-Bixler syndrome suggest that they might be related disorders and that the latter condition should be included in the bent-bone dysplasia group. Similarity between the metaphyseal regions of the scapula and the metaphyses of the long tubular bones in the different types of short-rib polydactyly syndrome illustrates the importance of evaluation of the scapula in this group as well as in other well-defined or unknown osteochondrodysplasias.

Multiple vertebral segmentation defects: analysis of 26 new patients and review of the literature.

To further delineate and classify those forms of short trunk dwarfism characterized by multiple vertebral segmentation defects, we analyzed 26 new patients and reviewed 115 described in the literature. Three distinct entities were recognized based on radiographic and clinical findings. Jarcho-Levin syndrome is the lethal autosomal recessive form, characterized by a symmetric crab-like chest. Spondylocostal dysostosis is the benign autosomal dominant condition. Spondylothoracic dysostosis shows considerable clinical and radiographic overlap with spondylocostal dysostosis. Malformations observed in association with multiple vertebral segmentation defects are more common in the sporadic patients. Analysis of the 26 new individuals revealed that the body segment in which these nonvertebral malformations occur corresponds to the site of the vertebral segmentation defects.

Pseudoachondroplasia and multiple epiphyseal dysplasia due to mutations in the cartilage oligomeric matrix protein gene.

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are dominantly inherited chondrodysplasias characterized by short stature and early-onset osteoarthrosis. The disease genes in families with PSACH and MED have been localized to an 800 kilobase interval on the short arm of chromosome 19. Recently the gene for cartilage oligomeric matrix protein (COMP) was localized to chromosome 19p13.1. In three patients with these diseases, we identified COMP mutations in a region of the gene that encodes a Ca++ binding motif. Our data demonstrate that PSACH and some forms of MED are allelic and suggest an essential role for Ca++ binding in COMP structure and function.