A novel G1006A substitution in the alpha 2(I) chain of type I collagen produces osteogenesis imperfecta type III

Identification and molecular characterization of two novel mutations in COL1A2 in two Chinese families with osteogenesis imperfecta

Osteogenesis imperfecta (OI, also known as brittle bone disease) is caused mostly by mutations in two type I collagen genes, COL1A1 and COL1A2 encoding the pro-α1 (I) and pro-α2 (I) chains of type I collagen, respectively. Two Chinese families with autosomal dominant OI were identified and characterized. Linkage analysis revealed linkage of both families to COL1A2 on chromosome 7q21.3-q22.1. Mutational analysis was carried out using direct DNA sequence analysis. Two novel missense mutations, c.3350A>G and c.3305G>C, were identified in exon 49 of COL1A2 in the two families, respectively. The c.3305G>C mutation resulted in substitution of a glycine residue (G) by an alanine residue (A) at codon 1102 (p.G1102A), which was found to be mutated into serine (S), argine (R), aspartic acid (D), or valine (V) in other families. The c.3350A>G variant may be a de novo mutation resulting in p.Y1117C. Both mutations co-segregated with OI in respective families, and were not found in 100 normal controls. The G1102 and Y1117 residues were evolutionarily highly conserved from zebrafish to humans. Mutational analysis did not identify any mutation in the COX-2 gene (a modifier gene of OI). This study identifies two novel mutations p.G1102A and p.Y1117C that cause OI, significantly expands the spectrum of COL1A2 mutations causing OI, and has a significant implication in prenatal diagnosis of OI.

Sequence of normal canine COL1A1 cDNA and identification of a heterozygous alpha1(I) collagen Gly208Ala mutation in a severe case of canine osteogenesis imperfecta

The sequence of canine COL1A1 cDNA was determined from four overlapping COL1A1 RT-PCR products generated from canine fibroblast RNA. In the translated region, nucleotide identity between canine and human COL1A1 cDNA was 93.2%, although the canine sequence lacked nucleotides 204 to 215 in the region coding for the N-propeptide. Amino acid identity was 97.7%. Total RNA and type I collagen were collected from cultured skin fibroblasts of a 12-week-old male golden retriever with pathologic fractures suggestive of osteogenesis imperfecta (OI) and dentinogenesis imperfecta. Sequential, overlapping approximately 1,000-bp fragments of COL1A1 and COL1A2 cDNA were each amplified by RT-PCR using primers containing 5' T7 polymerase sites. These PCR products were transcribed with T7 RNA polymerase, hybridized into RNA duplexes, and cleaved at mismatch sites with RNase. The proband had an unique cleavage pattern for the fragment of COL1A1 mRNA spanning nucleotides 709 to 1,531. Sequence analysis identified a G to C point mutation for nucleotide 1,276, predicting a codon change from glycine (GGA) to alanine (GCA) for amino acid 208. This change disrupts the normal Gly-X-Y pattern of the collagen triple helix. Restriction enzyme digestion of the RT-PCR product was consistent with a heterozygous COL1A1 mutation. Type I collagen was labeled with 3H-proline, salt precipitated, and analyzed by SDS-PAGE. Pepsin digested alpha chains were over-hydroxylated, and procollagen processing was delayed. Thus, canine and human OI appear homologous in terms of clinical presentation, etiology, and pathogenesis.

Multiple epiphyseal dysplasia and pseudoachondroplasia due to novel mutations in the calmodulin-like repeats of cartilage oligomeric matrix protein

A child with a mild form of pseudoachondroplasia was heterozygous for a deletion of 12 nucleotides from exon 10 of the cartilage oligomeric matrix protein (COMP) gene. It resulted in the deletion of valine 513 to lysine 516 from the eighth calmodulin-like repeat of COMP monomers. A child with the Fairbank's type of multiple epiphyseal dysplasia was also heterozygous for a COMP mutation. It substituted cysteine 371 by serine in the fourth calmodulin-like repeat. Both mutations were likely to alter the conformation and calcium binding of the mutant COMP protein chains. These findings support the proposal that deletions and insertions within the calmodulin-like domain produce pseudoachondroplasia, while amino acid substitutions with this domain may produce either pseudoachondroplasia or multiple epiphyseal dysplasia.

Disrupted growth plates and progressive deformities in osteogenesis imperfecta as a result of the substitution of glycine 585 by valine in the alpha 2 (I) chain of type I collagen

The skeleton of a child with osteogenesis imperfecta type III, resulting from the substitution of glycine 586 by valine in the triple helical domain of the alpha 2 (I) chain of type I collagen, was severely porotic but contained lamellar bone and Haversian systems. From early childhood, structural failure of the bone resulted in the disruption of growth plates, progressive bone deformities, and severe growth retardation.

Alternative splicing of exon 12 of the COL2A1 gene interrupts the triple helix of type-II collagen in the Kniest form of spondyloepiphyseal dysplasia

An autosomal dominant mutation in the COL2A1 gene was identified in a child with the Kniest form of spondyloepiphyseal dysplasia. A C to T transition at nucleotide 35 of exon 12 changed the codon GCG for alanine 102 of the triple helical domain of alpha 1(II) chains of type-II collagen to GTG for valine. The transition also introduced a GT dinucleotide into exon 12. Analysis of cDNA prepared from Kniest cartilage showed that in vivo the transition resulted in an alternatively spliced mRNA that lacked the 213' nucleotides from exon 12. The cartilage cDNA contained approximately equal amounts of normal cDNA and shortened mutant cDNA. The deletion of 21 nucleotides from the mutant cDNA maintained the translational reading frame but resulted in the loss of alanine 102 to lysine 108, which interrupted the repetitive glycine-X-Y triplet sequence required for formation of the triple helix. Type-II collagen molecules containing one or more mutant chains were expected, therefore, to contain interrupted triple helices with a short amino-terminal helical domain A and a large carboxy-terminal helical domain B. Kniest cartilage contained a reduced amount of pepsin-solubilized type-II collagen that consisted of overmodified alpha 1(II) chains. Peptide mapping showed that the overmodifications extended to the carboxy terminus of the alpha 1(II) chains. Pepsin digestion also yielded shortened alpha 1(II) chains corresponding to helical domain B. Kniest chondrocytes cultured in alginate beads produced type-II collagen that was not stably incorporated into the pericellular matrix. This study highlights the importance of dominant negative mutations of COL2A1 in producing Kniest dysplasia.

Arachnoid cyst and chronic subdural haematoma in a child with osteogenesis imperfecta type III resulting from the substitution of glycine 1006 by alanine in the pro alpha 2(I) chain of type I procollagen

The features of a child with osteogenesis imperfecta type III (OI III) resulting from the heterozygous substitution of glycine 1006 by alanine in the pro alpha 2(I) chain of type I procollagen were studied. He was born at term with the clinical features of severe OI, including deep grey-blue sclerae. He had severe osteopenia and all long bones were smaller than normal with cortical thinning, metaphyseal expansion, poor metaphyseal modelling, and multiple fractures. However, the vertebrae, pelvis, and shoulder girdle were of normal shape and there were few rib fractures. Histological examination of the calvarium and tibial shaft showed woven bone without lamellar bone or Haversian systems. The shafts of the long bones were widened owing to repeated fractures. Progressive enlargement of the calvarium occurred between 3 and 4.5 months of age owing to bilateral chronic subdural haematomata and a large arachnoid cyst in the Sylvian fissure. The cyst was probably developmental in origin while the subdural collections were probably the result of perinatal skull trauma. The cyst and the subdural collections resolved following drainage but ventricular dilatation with normal cerebrospinal fluid pressure followed. The proband is the first reported case of OI with a glycine substitution by alanine in the pro alpha 2(I) chain of type I procollagen.