Three new polymorphisms at the COL1A2 locus

Ehlers-Danlos syndrome type VII: clinical features and molecular defects

We evaluated the clinical features, molecular defects, and problems associated with the management of two patients who had type-VII Ehlers-Danlos syndrome and reviewed the cases of eighteen patients with this condition who had been reported on previously. The typical clinical features associated with this syndrome include bilateral congenital dislocation of the hip; severe generalized hypermobility of the joints; multiple dislocations of joints other than the hip; muscular hypotonia; and hyperelasticity, fragility, and a doughy texture of the skin. Collagen and DNA analyses demonstrated that both of our patients had type-VIIB Ehlers-Danlos syndrome, which is caused by heterozygous new mutations of the COL1A2 gene that encodes the proalpha2(I) chain of type-I procollagen. The obligatory GT dinucleotide at the splice donor site of intron 6 was altered in both of our patients: one patient (Case 1) had an A substitution of the G nucleotide, and the other patient (Case 2) had a C substitution of the T nucleotide. Abnormal splicing resulted in the loss of the exon 6-encoded N-telopeptide, which includes the N-proteinase cleavage site. Despite multiple operative procedures, one of our patients, who was thirty-seven years old at the time of the most recent follow-up, continued to have persistent subluxation of the right hip and osteoarthritis of the left hip. Closed reduction of the dislocated hips, regardless of the type of immobilization used, was unsuccessful in all twenty patients. The results of open reduction were improved when capsulorrhaphy was combined with iliac or femoral osteotomy, or both.

The human type I collagen mutation database

Type I collagen is the most abundant and ubiquitously distributed of the collagen family of proteins. It is a heterotrimer comprising two alpha1(I) chains and one alpha2(I) chain which are encoded by the unlinked loci COL1A1 and COL1A2 respectively. Mutations at these loci result primarily in the connective tissue disorders osteogenesis imperfecta and Ehlers-Danlos syndrome types VIIA and VIIB. Two instances of osteoporosis and a single instance of Marfan syndrome are also the result of mutations at these loci. The mutation data are accessible on the world wide web at http://www.le.ac.uk/depts/ge/collagen/collagen.html

Direct sequencing of PCR products derived from cDNAs for the pro alpha 1 and pro alpha 2 chains of type I procollagen as a screening method to detect mutations in patients with osteogenesis imperfecta

More than 150 mutations in the genes for type I procollagen have been found in unrelated patients with osteogenesis imperfecta (OI), but mutations have been difficult to define in many patients with the mildest forms of the disease. Here, we have used robotically automated sequencing of the cDNAs for type I procollagen to screen for mutations in 12 patients suspected of having nonlethal OI (types I, III, and IV). Single base mutations that changed codons for obligate glycine residues were found in seven of the patients. Altogether, we analyzed 4,379 bp of sequences of both alleles of the pro alpha 1 (I) collagen (8,758 bp of allelic sequences) and 4,200 bp of sequences of both alleles of the pro alpha 2(I) collagen (8,400 bp of allelic) from each patient.

Mutation analysis of coding sequences for type I procollagen in individuals with low bone density

Mutations in one of the two genes encoding type I procollagen (COL1A1 and COL1A2) are frequently the cause of osteogenesis imperfecta (OI), a disorder characterized by brittle bones. Here we tested whether patients with low bone density also have mutations in these genes. The 26 patients studied had no apparent metabolic bone disease, but most had a positive family history of osteopenia or osteoporosis. Although a diagnosis of OI was considered by the clinician in some cases, the clinical criteria for OI were not satisfied. Our strategy for mutation analysis consisted of PCR amplification of cDNA made to fibroblast mRNA using primers specific for the coding regions of COL1A1 and COL1A2. The PCR products were then sequenced directly with primers located within each PCR product. We found that 3 of 26 patients had mutations that altered the encoded amino acid. One mutation, at position alpha 2(I)-661 has been reported (Spotila et al. 1991 Proc Natl Acad Sci USA PNAS 88:5423). The other 2 patients, who were not related to each other, had a mutation that altered the proline codon at alpha 1(I)-27 to alanine. This mutation was not found in 81 normal individuals or in 37 additional osteopenic individuals. However, its effect on the biologic function of type I collagen, as well as its role in osteopenia, is uncertain. In addition to the two mutations, we found a polymorphism in codon alpha 2(I)-459. Although this polymorphism involved an amino acid substitution, it was present with equal frequency in the patient and the normal population. By analyzing this and previously reported neutral sequence variants in the COL1A2 gene, we determined that all patients expressed both alleles of the COL1A2 gene. The 12 patients who were heterozygous for a COL1A1 neutral sequence variant also expressed both alleles. Here we present all PCR primer and sequencing primer information. The results suggest that surveying a larger group of similarly selected individuals may reveal additional mutations in the COL1A1 or COL1A2 genes.

Identification of type I collagen gene polymorphisms: tolerance of sequence variation at an alpha 2(I) helix Y position

This study has examined the frequency and distribution of polymorphisms in the type I collagen coding sequences. RNA from a group of human skin fibroblast cell lines was analyzed by the chemical cleavage mismatch detection method using hydroxylamine, a reagent specific for C-base mismatches, and overlapping cDNA probes covering the entire prepro alpha 1(I) and prepro alpha 2(I) coding regions. Mismatches were detected at only two nucleotide positions, one in each of the type I collagen sequences, suggesting that polymorphisms are relatively rare within these cDNAs. cDNA sequence analysis demonstrated that the prepro alpha 1(I) mismatch, detected in only one cell line, was due to a sequence polymorphism involving the wobble position of the codon for arginine residue 59 within the amino-propeptide globular subdomain of the pro alpha 1(I) chain and not resulting in a change in the polypeptide primary structure. In contrast, the prepro alpha 2(I) mismatch, detected in 6 of the 16 cell lines, was shown to arise from a sequence polymorphism affecting the identity of Y-position residue 459 of the alpha 2(I) triple helical domain, resulting in an alanine/proline dimorphism at this position. This study is the first to identify a type I collagen coding sequence polymorphism resulting in an alteration at the level of the amino acid sequence. The data suggest that at least some alpha 1(I) and alpha 2(I) helix Y positions may be tolerant of sequence variation, particularly if the replacing amino acid is proline, a residue involved in stabilizing the collagen triple helix.