Collagen, Type Ii, Alpha-1

Description

Collagens are major structural components of the extracellular matrix. Type II collagen, also called cartilage collagen, is the major collagen synthesized by chondrocytes. The same type of collagen occurs in the vitreous. Type II collagen is comprised of 3 alpha-1(II) chains. These are synthesized as larger procollagen chains, which contain N- and C-terminal amino acid sequences called propeptides. After secretion into the extracellular matrix, the propeptides are cleaved, forming the mature type II collagen molecule (summary by Strom and Upholt, 1984 and Cheah et al., 1985).

Cloning and Expression

Strom and Upholt (1984) isolated overlapping genomic DNA clones containing most of the coding sequences for chicken type II procollagen. They found that the chicken type II gene is 2 to 3 times more compact than the chicken type I alpha-2 gene (COL1A2; 120160) due to smaller introns. The coding sequence shows about 75% homology with type I alpha-1 (COL1A1; 120150) and 63 to 67% homology with type I alpha-2 and type III (COL3A1; 120180) sequences. Base composition and codon usage of type II are very similar to alpha-1(I) and different from alpha-2(I) and type III. The chicken type II gene appears to be present in single copy per haploid genome. Using probes corresponding to the chicken COL2A1 procollagen gene to screen a recombinant human DNA library, Strom and Upholt (1984) isolated a portion of the human COL2A1 gene.

Sangiorgi et al. (1984) isolated from a cartilage cDNA library a bovine clone encoding the pro-alpha-1(II) collagen chain. Because of the close homology of bovine and human collagens, the bovine clone could be used to isolate the corresponding gene from a human genomic library.

By comparison of amino acid sequences, van der Rest et al. (1986) showed that chondrocalcin is the C-propeptide of type II procollagen. Chondrocalcin is a calcium-binding protein found in developing fetal cartilage matrix and in growth plate cartilage when and where mineralization occurs in the lower hypertrophic zone. It appears to play a role in enchondral ossification. The new evidence on its identity to C-propeptide indicates that it is also important in assembly of the triple helix of type II collagen. See 156550 for evidence of abnormal processing of the C-propeptide of type II collagen resulting in imperfect fibril assembly and the clinical disorder called Kniest dysplasia.

Studying the gerbil, Slepecky et al. (1992) demonstrated that types II and IX (120210) collagen show colocalization in the inner ear.

Wu and Eyre (1995) provided evidence that what was formerly termed the alpha-3 chain of type XI collagen (COL11A3) is actually transcribed from the COL2A1 gene.

Mapping

By analysis of DNA from human-mouse cell hybrids, Sangiorgi et al. (1984) localized the COL2A1 gene to chromosome 12. The results were confirmed by similar experiments with the bovine cDNA probe. Using a cloned gene as a probe on Southern blots of DNA from a panel of interspecies somatic cell hybrids, Solomon et al. (1985) also assigned the COL2A1 locus to chromosome 12.

By somatic cell hybrid studies and in situ hybridization, Huerre-Jeanpierre et al. (1986) assigned COL2A1 to 12q13.1-q13.2 and COL3A1 to 2q31-q32.3. Law et al. (1986) used a cosmid clone of the entire COL2A1 gene in Southern analysis of DNA from somatic cell hybrids containing segments of chromosome 12. Two hybrids contained a similar terminal deletion of 12q14.3-qter but 1 was positive for the gene and 1 negative. This led Law et al. (1986) to conclude that the gene is located in 12q14.3.

Takahashi et al. (1990) described a 'new' nonisotopic method of in situ hybridization. It involved replication of R-bands by incorporation of bromodeoxyuridine (BrdU) into cells synchronized with thymidine. Fluorescent signals could be detected on R-banded prometaphases stained with propidium iodide. They illustrated the strength of the system by refining the localization of the COL2A1 gene to 12q13.11-q13.12. By nonisotopic in situ hybridization, Takahashi et al. (1990) showed that the COL2A1 gene is immediately proximal to the fragile site fra(12)(q13.1).

Gene Function

Lovell-Badge et al. (1987) introduced a cosmid containing the human type II collagen gene, including 4.5 kb of 5-prime and 2.2 kb of 3-prime flanking DNA, into mouse embryonic cells in vitro. Human type II collagen mRNA was found only in tissues that showed transcription from the endogenous (mouse) gene, and human type II collagen was found in cartilage. The findings indicated that the cis-acting requirements for correct temporal and spatial regulation of the gene were fulfilled by the introduced DNA.

Molecular Genetics

Several skeletal and ocular disorders have been found to be caused by mutation in the COL2A1 gene. These are sometimes referred to as type II collagenopathies.

Spondyloepiphyseal Dysplasia Congenita

The first evidence for a defect in COL2A1 in SED congenita (183900) and in Langer-Saldino achondrogenesis (200610) was the finding of abnormal patterns of digestion of type II collagen by cyanogen bromide, as demonstrated by Horton (1987). Confirmation of the defect in SED congenita was provided by demonstration of mutation in COL2A1 (120140.0001 and 120140.0002).

Achondrogenesis Type II

Godfrey and Hollister (1988) presented evidence that the patient they studied with a lethal perinatal form of short-limbed dwarfism (200610) was heterozygous for an abnormal pro-alpha-1(II) chain which impaired the assembly and/or folding of type II collagen. Vissing et al. (1989) demonstrated that the mutation in the type II procollagen gene was a single base change that converted the codon for glycine (GGC) at amino acid 943 to a codon for serine (AGC) (120140.0002).

Stickler Syndrome, Type I

Francomano et al. (1987, 1987) demonstrated absolute linkage of COL2A1 and Stickler syndrome (STL1; 108300); a total lod score of 3.96 at theta = 0.0 was obtained. In a family with Stickler syndrome, Ahmad et al. (1990, 1991) identified a mutation in the COL2A1 gene (120140.0005).

Mutation in the COL2A1 gene (120140.0014) has also been found in a nonsyndromic ocular form of type I Stickler syndrome (609508).

In a patient with Stickler syndrome type I, who had a clinical diagnosis of otospondylomegaepiphyseal dysplasia (OSMED; 215150), Miyamoto et al. (2005) identified a splice acceptor mutation in intron 10 (709-2A-G; 120140.0048) of the COL2A1 gene.

Osteoarthritis Associated with Chondrodysplasia

Knowlton et al. (1989) found tight linkage (no recombination) of the COL2A1 gene with a precocious form of familial primary generalized osteoarthritis (OA) associated with chondrodysplasia (604864). In the full report of this family, Knowlton et al. (1990) stated that a 16-year-old male had osteoarthritis of the middle metacarpophalangeal joints and hips as well as bilateral osteochondritis dissecans of the capitellum. A 38-year-old female also had osteoarthritis of the spine, wrists, proximal interphalangeal joints, and distal interphalangeal joints. Vertebral bodies were flattened with Schmorl nodes. Linkage analysis suggested that the mutation is in the COL2A1 locus with a maximum lod score of 2.39 in multipoint analysis. Morphometrics demonstrated a short trunk producing abnormally low upper segment to lower segment ratio. A mutation in the COL2A1 gene (120140.0003) in affected members of the kindred described by Knowlton et al. (1990) was identified by Ala-Kokko et al. (1990).

Nelson et al. (1998) presented further evidence that the synthesis of type II collagen is increased in osteoarthritis. Using an immunoassay, they showed that the content of the C-propeptide of type II procollagen, released extracellularly from the newly synthesized molecule, is directly related to the synthesis of this molecule in healthy and osteoarthritic articular cartilage. In OA cartilage, the content of the type II procollagen is often markedly elevated (mean 7.6-fold). The increase in type II procollagen in OA cartilage was not reflected in serum, where a significant reduction was observed.

Kniest Dysplasia

Wilkin et al. (1999) noted that 10 of 12 previously described dominant mutations in the COL2A1 gene in patients with Kniest dysplasia caused small deletions in the type II collagen molecule. They added 4 new mutations, bringing the total to 16. All 4 new mutations were also small deletions; a fifth patient was found to have a previously reported 28-bp deletion (120140.0012).

COL2A1 has 10 in-frame CGA codons that can mutate to TGA stop codons by a methylation-deamination mechanism. Wilkin et al. (2000) analyzed these 10 codons using restriction endonuclease analysis or allele-specific amplification. Mutations at 5 COL2A1 CGA codons were identified in 8 of 40 patients with Stickler syndrome, suggesting that these are common sites of mutation in this disorder.

Korkko et al. (2000) performed COL2A1 mutation analysis on 12 patients with achondrogenesis type II/hypochondrogenesis, using conformation sensitive gel electrophoresis, followed by sequencing. Mutations were identified in all patients. Ten had single base substitutions, 1 had a change in a consensus RNA splice site, and 1 was an 18-bp deletion of coding sequences. Mutations were widely distributed across the gene.

In 2 sporadic cases of the Torrance type of platyspondylic skeletal dysplasia (151210), Nishimura et al. (2004) identified de novo mutations in the COL2A1 gene (120140.0039-120140.0040).

Avascular Necrosis of the Femoral Head and Legg-Calve-Perthes Disease

Avascular necrosis of the femoral head (see ANFH1, 608805) causes disability that often requires surgical intervention. Most cases of ANFH are sporadic, but Liu et al. (2005) identified 3 families in which there was autosomal dominant inheritance of the disease with mapping of the phenotype to 12q13. Liu et al. (2005) carried out haplotype analysis in the families, selected candidate genes from the critical interval for an ANFH on 12q13, and sequenced the promoter and exonic regions of the COL2A1 gene from persons with inherited and sporadic forms of ANFH. In 2 of the families they identified the same gly1170-to-ser mutation (120140.0043), on different haplotype backgrounds. The gly717-to-ser mutation was detected in the third family (120140.0044).

Miyamoto et al. (2007) identified the gly1170-to-ser mutation (120140.0043) in affected members of a Japanese family with an autosomal dominant disorder manifesting as Legg-Calve-Perthes disease (LCPD; 150600), a form of ANFH in growing children.

In a 40-year-old man who was diagnosed with avascular necrosis of the femoral head at 18 years of age and underwent bilateral hip replacement at 33 years of age, Kannu et al. (2011) identified a heterozygous missense mutation in the C-propeptide region of the COL2A1 gene (120140.0054). The authors noted that mutations in the C-propeptide region typically cause significant skeletal findings unlike those found in this patient.

Other Disorders Caused by COL2A1 Mutations

Other disorders caused by mutation in the COL2A1 gene include spondylometaphyseal dysplasia (SMD; 184252; see 120140.0013); Strudwick type of spondyloepimetaphyseal dysplasia (184250; see 120140.0017); multiple epiphyseal dysplasia with myopia and conductive deafness (132450; see 120140.0029); spondyloperipheral dysplasia (271700; see 120140.0030); platyspondylic skeletal dysplasia, Torrance type (151210; see 120140.0039); Czech dysplasia (609162; see 120140.0018); rhegmatogenous retinal detachment (see 609508; see 120140.0045); vitreoretinopathy with phalangeal epiphyseal dysplasia (120140.0037); and Stanescu type of spondyloepiphyseal dysplasia (SEDSTN; 616583; see 120140.0055).

Machol et al. (2017) reported 2 unrelated patients diagnosed with the corner fracture type of spondylometaphyseal dysplasia (see SMDCF, 184255) in whom heterozygous mutations in the COL2A1 gene were reported, G345D and G945S, respectively. The G345D mutation had previously been detected in a patient diagnosed with the Strudwick type of spondyloepimetaphyseal dysplasia (SEMDSTWK, 184250) by Barat-Houari et al. (2016), and the G945S mutation had previously been reported by Terhal et al. (2015) in 5 affected members of a Dutch family diagnosed with mild spondyloepiphyseal dysplasia congenita resembling multiple epiphyseal dysplasia (see EDM1, 132400). Noting that Walter et al. (2007) also described a COL2A1-mutated patient with primarily metaphyseal involvement and apparent 'corner fractures,' Machol et al. (2017) suggested that SMDCF may be a heterogeneous disorder with a subset of patients showing overlap with type II collagenopathies.

Somatic Mutation in Chondrosarcoma

Tarpey et al. (2013) reported comprehensive genomic analyses of 49 individuals with chondrosarcoma (215300) and identified hypermutability of the major cartilage collagen gene COL2A1, with insertions, deletions, and rearrangements identified in 37% of cases. The patterns of mutation were consistent with selection for variants likely to impair normal collagen biosynthesis. In addition, Tarpey et al. (2013) identified mutations in IDH1 (147700) or IDH2 (147650) (59%), TP53 (191170) (20%), the RB1 pathway (see 614041) (33%), and Sonic hedgehog signaling (600725) (18%).

Associations Pending Confirmation

Helfgott et al. (1991) suggested that collagen type II may not only be involved in the sensorineural deafness that accompanies hereditary disorders such as spondyloepiphyseal dysplasia congenita and Stickler syndrome but may also be the target of an autoimmune process in some cases of acquired bilateral progressive sensorineural hearing loss.

Genotype/Phenotype Correlations

Liberfarb et al. (2003) performed genotype/phenotype correlations in 47 affected members from 10 families with 7 defined mutations in the COL2A1 gene based on review of medical records and clinical evaluation of 25 additional family members from 6 of the 10 families. The ages ranged from 2 to 73 years with a mean age of 34.7 years. The classic Stickler phenotype was expressed clinically in all 10 Stickler families with COL2A1 mutations and all had evidence of vitreous degeneration type 1. Myopia was present in 41 of 47 family members. There was considerable interfamilial and intrafamilial variability in clinical expression. The prevalence of certain clinical features was a function of age. Liberfarb et al. (2003) concluded that it is difficult to predict the severity of the phenotype based on the genotype of COL2A1 mutation.

Nishimura et al. (2005) searched for COL2A1 mutations in 56 families suspected of having type II collagenopathies and found 38 mutations in 41 families. There were no radiologic differences between the cases with and those without mutations. Phenotypes for all 22 missense mutations and 1 in-frame deletion in the triple-helical region fell along the SED spectrum. Glycine-to-serine substitutions resulted in alternating zones that produced more severe and milder phenotypes; glycine-to-nonserine residue substitutions exclusively created more severe phenotypes. The gradient of the SED spectrum did not necessarily correlate with the occurrence of extraskeletal manifestations. All 9 truncation or splice site mutations in the triple-helical or N-propeptide region caused either Stickler syndrome type I or Kniest dysplasia (156550), and extraskeletal changes were consistently present in both phenotypes. All 6 C-propeptide mutations produced a range of atypical skeletal phenotypes and created ocular, but not otolaryngologic, changes.

Hoornaert et al. (2006) noted that the majority of COL2A1 mutations are substitutions of obligatory glycine residues in the triple-helical domain; of the few nonglycine missense mutations that have been reported, arginine-to-cysteine substitutions predominate. Hoornaert et al. (2006) investigated the clinical and radiologic phenotype in 11 patients in whom they had identified arg-to-cys mutations in the COL2A1 gene. 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 (120140.0018), R519C (120140.0003), or R1076C mutation. Short third and fourth toes were a distinguishing feature of the R75C mutation, and brachydactyly with enlarged finger joints was a key feature of the R1076C substitution. Stickler dysplasia with brachydactyly was observed in patients with the R704C (120140.0029) mutation. The R365C (120140.0033) and R789C (120140.0016) mutations resulted in classic Stickler dysplasia and spondyloepiphyseal dysplasia congenita, respectively.

Barat-Houari et al. (2016) screened the COL2A1 gene in a cohort of 136 probands with clinical and/or radiographic suspicion of a type II collagen disorder. The authors identified 66 different mutations, spread throughout the COL2A1 gene, in 71 probands. They noted that the molecular spectrum was different across various diseases, e.g., all variant types were seen in Stickler syndrome, whereas only missense variants were seen in SEDC. Barat-Houari et al. (2016) stated that their results demonstrated the limits of focusing on a single gene for genetic diagnosis, given the lack of clear phenotype-to-genotype correlation, and suggested that a targeted next-generation sequencing approach should be used to screen patients with skeletal dysplasias for other candidate genes.

Reviews

Kuivaniemi et al. (1997) tabulated all reported disease-producing mutations in the COL2A1 gene.

Animal Model

Vandenberg et al. (1991) found that transgenic mice carrying a partially deleted human COL2A1 gene developed the phenotype of a chondrodysplasia with dwarfism, short and thick limbs, short snout, cranial bulge, cleft palate, and delayed mineralization of bone. In cultured chondrocytes from transgenic mice, the minigene was expressed as shortened pro-alpha-1(II) chains that were disulfide-linked to normal mouse type II collagen chains. Therefore, the phenotype was probably explained by depletion of endogenous mouse type II procollagen through the phenomenon of procollagen suicide. Garofalo et al. (1991) generated transgenic mice harboring a glycine-to-cysteine mutation at residue 85 of the triple-helical domain of mouse type II collagen. Offspring displayed severe chondrodysplasia with short limbs and trunk, craniofacial deformities, and cleft palate. Affected pups died of acute respiratory distress caused by inability to inflate the lungs at birth. Electron microscopic analysis showed a pronounced decrease in the number of typical thin cartilage collagen fibrils, distention of the rough endoplasmic reticulum of chondrocytes, and the presence of abnormally large banded collagen fibril bundles. Garofalo et al. (1991) postulated that the abnormally thick collagen bundles were related to a defect in crosslinking. They pointed out similarities to the chondrodysplasias of the spondyloepiphyseal dysplasia group.

Li et al. (1995) used homologous recombination in embryonic stem cells to prepare transgenic mice with an inactivated COL2A1 gene. Heterozygous mice had minimal phenotypic changes. Homozygous mice were delivered vaginally but died either just before or shortly after birth. In these mice the cartilage consisted of highly disorganized chondrocytes with a complete lack of extracellular fibrils discernible by electron microscopy. There was no endochondral bone or epiphyseal growth plate in long bones; however, many skeletal structures such as the cranium and ribs were normally developed and mineralized. Li et al. (1995) concluded that a well-organized cartilage matrix is required as a primary tissue for development of some components of the skeleton but is not essential for others.

Gaiser et al. (2002) constructed a transgenic mouse model of SED congenita using a type II collagen transgene with an arg789-to-cys change (R789C; 120140.0016) in combination with a murine Col2a1 promoter directing the gene expression to cartilage. Mice carrying the transgene were shorter overall, had shorter limbs with disorganized growth plates, a short nose, cleft palate, and died at birth. Using cell culture experiments and molecular modeling, Gaiser et al. (2002) suggested that this Y-position mutation acts in a dominant-negative way, resulting in destabilization of collagen molecules during assembly, reduction in the number of fibrils formed, and abnormal cartilage template function. Donahue et al. (2003) identified a naturally occurring arg1147-to-cys mutation in the Col2a1 gene in the mouse which resulted in recessive SED congenita with a less severe phenotype, as indicated by the fact that the mice survived to adulthood and reproduced normally.

History

The following is an account of a temporarily confusing aspect of the collagen II gene. Weiss et al. (1982) described a collagen gene isolated in a 40-kb cosmid clone, cosHco11, which has some sequence homology to the alpha-1(I) gene, but which is clearly a different gene. Using this collagen alpha-1(I)-like probe on Southern blots of DNA from somatic cell hybrids, Solomon et al. (1984) found that the gene segregated with chromosome 12 and is not syntenic with the alpha-2(I) gene assigned to chromosome 7 (120160) or the alpha-1(I) gene assigned to chromosome 17 (120150). This gene contains an RFLP with HindIII. A 300-basepair deletion in the alpha-1(I)-like gene mapped by Solomon et al. (1984) was demonstrated by Pope et al. (1984) in a father and son with one form of Ehlers-Danlos syndrome II (EDS II; 130010). The deletion was found at or near the 3-prime end of the gene and was not identified in other cases of EDS II or in 400 normal controls. It was found, however, in 4 babies with lethal osteogenesis imperfecta congenita. The father and son with EDS II and the deletion showed altered collagen fibril size and shape. Subsequently, the 'alpha-1(I)-like' gene was shown to encode the alpha subunit of cartilage collagen and it was further shown that there is a polymorphism in this gene that is frequent in Asiatic Indians (Sykes et al., 1985). Of the 4 cases of Pope et al. (1984), 3 originated from India or Sri Lanka. This experience illustrates the hazards of confusing polymorphism with pathology.

Meulenbelt et al. (1996) determined the allele frequencies and pairwise linkage disequilibria of RFLPs distributed over the COL2A1 gene in a population of unrelated Dutch Caucasians. Their data indicated that disease-related population studies should include a minimum of 4 RFLPs.

Strom (1984) purported to find abnormality of the type II collagen gene in achondroplasia. If such a defect were present, one would expect ocular abnormality in achondroplasia inasmuch as type II collagen is present in vitreous. SED congenita is a more plausible candidate for a structural defect of type II collagen because it is a dominant disorder that combines skeletal dysplasia with vitreous degeneration and deafness (experimental studies with antibodies to type II collagen indicate that this collagen type is represented in the inner ear; Yoo et al., 1983). The work of Strom (1984) may be technically flawed.