The COL1A2 gene is associated with autosomal dominant osteogenesis imperfecta (MedGen UID: 45246) and Ehlers-Danlos syndrome, arthrochalasia type (MedGen UID: 78662). The COL1A2 gene is also associated with autosomal recessive Ehlers-Danlos syndrome, cardiac valvular form (MedGen UID: 347359).
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Together, pathogenic variants in COL1A1 and COL1A2 cause >90% of clinical cases of Osteogenesis Imperfecta types I, II, III, and IV and are the only known cause of Ehlers-Danlos, arthrochalasia type. Pathogenic variants in COL1A2 are the only known cause of Ehlers-Danlos syndrome, cardiac valvular form.
The COL1A2 gene encodes pro-alpha2(I) that, along with pro-alpha 1(I), forms type I collagen (PMID: 23692737). Type I collagen is the most abundant form of collagen, which strengthens and supports bones, cartilige, tendons, teeth, skin and the sclera of the eye (PMID: 23692737).
MedGen UID: 45246
COL1A1 (OMIM 129150) and COL1A2 (OMIM 120160) are associated with osteogenesis imperfecta (OI), a disorder characterized by bone fragility. Pathogenic variants in COL1A1 and COL1A2 are identified in over 90% of individuals with OI, and testing for these variants is recommended in individuals with a personal or family history of fractures not caused by trauma. Some affected individuals exhibit joint laxity and easy bruisability. Identifying radiologic findings include wormian bones, codfish vertebrae, evidence of old, healed fractures, and osteopenia (PMID: 20301472).
Testing for COL1A1 and COL1A2 is often recommended in infants and children with unexplained fractures. Diagnostic clinical and radiologic findings may not be relevant in these situations (PMID: 26566591).
Most cases of OI type I (OMIM 166200) are caused by pathogenic variants in COL1A1. Pathogenic variants in either COL1A1 or COL1A2 are associated with OI types II (OMIM 166210), III (OMIM 259420), and IV (OMIM 166220). OI type I is the mildest form, with affected individuals typically exhibiting blue/gray sclerae and hearing loss in adulthood. OI type II is the most severe and can be life threatening in infancy. Other types of OI have signs and symptoms that vary in severity. (PMID: 20301472, National Library of Medicine. Genetics Home Reference. Osteogenesis Imperfecta. https://ghr.nlm.nih.gov/condition/osteogenesis-imperfecta. Accessed May 2017).
Ehler-Danlos Syndrome (EDS; OMIM 13000) is a heterogenous group of connective tissue disorders, which have some overlap with OI. Typically, affected individuals with EDS have pathogenic variants in COL5A1 and COL5A2, although COL1A1 and COL1A2 pathogenic variants have also been identified in this patient population (PMID: 15580559).
When a short stature syndrome is identified in utero, hypophosphatasia, thanatophoric dysplasia, campomelic dysplasia, and achondroplasia may be considered in addition to a perinatal form of OI (PMID: 19265753).
Additionally, a form of autosomal dominant dentinogenesis imperfecta exists that is distinct from OI (National Library of Medicine. Genetics Home Reference. Dentinogenesis Imperfecta. https://ghr.nlm.nih.gov/condition/dentinogenesis-imperfecta. Accessed May 2017).
Pathogenic variants in CRTAP and P3H1 are associated with rare, often severe, autosomal recessive forms of OI type VII (OMIM 610682) and VIII (OMIM 610915) (PMID: 19550437, National Library of Medicine. Genetics Home Reference. CRTAP gene. https://ghr.nlm.nih.gov/gene/CRTAP. P3H1 gene. https://ghr.nlm.nih.gov/gene/P3H1. Accessed May 2017).
The COL1A1 gene codes for pro-alpha1 chains of type I collagen, which belongs to a family of proteins that provide support to many skeletal tissues (National Library of Medicine. Genetics Home Reference. COL1A1 gene. https://ghr.nlm.nih.gov/gene/COL1A1. Accessed May 2017; NCBI. Gene. Gene ID: 1277. https://www.ncbi.nlm.nih.gov/gene/1277. Accessed May 2017). Type I collagen is composed of three chains of pro-collagen molecules: two pro-alpha1 chains and one pro-alpha2 chain, which is produced by the COL1A2 gene (National Library of Medicine. Genetics Home Reference. COL1A2 gene. https://ghr.nlm.nih.gov/gene/COL1A2. Accessed May 2017; NCBI. Gene. Gene ID: 1278. https://www.ncbi.nlm.nih.gov/gene/1278. Accessed May 2017). Pathogenic variants in COL1A1 reduce the amount of type I collagen, leading to the bone fragility.
A mutation in COL1A1 is thought to be the cause of Caffey disease, which presents in infancy with hyperostosis or excessive bone formation, joint swelling, and pain. The symptoms usually improve with age, but joint laxity may persist (National Library of Medicine. Genetics Home Reference. Caffey disease. https://ghr.nlm.nih.gov/condition/caffey-disease. Accessed May 2017).
COL1A1 and COL1A2 show autosomal dominant inheritance. This means that an individual with a pathogenic variant in COL1A1 or COL1A2 has a 50% chance of passing the condition on to their offspring. With this result, it is possible to identify at-risk relatives who can pursue testing for this specific familial variant. OI may be inherited from a parent, but many cases occur spontaneously (in 60% to 100% of affected individuals depending on the OI subtype; PMID: 20301472). OI may be inherited in an autosomal recessive fashion but it is less common.
Treatment by a multidisciplinary team is highly recommended. For a list of OI treatment centers, please see the OI Clinic Directory.
Affected individuals are seen by orthopedists, orthopedic surgeons, pediatric dentists, and rehabilitation specialists. Evaluations for hearing, bone density, scoliosis, vertebral compression fractures, and assessment for craniocervical junction abnormalities are necessary (PMID: 28009709). Surgery presents a particular set of potential problems for affected individuals necessitating appropriate evaluations. Evidence also suggests that there may be some cardiovascular implications for OI patients (PMID: 2764717).
It is common for individuals with OI to receive either IV or oral bisphosphonate therapy. Bisphosphonates increase bone density and decrease fracture rates in affected children and adults, although the extent to which they improve clinical well-being is still debated (PMID: 27760454). New therapies are currently under development (PMID: 27813341).
Review date: May 2017
Invitae is a College of American Pathologists (CAP)-accredited and Clinical Laboratory Improvement Amendments (CLIA)-certified clinical diagnostic laboratory performing full-gene sequencing and deletion/duplication analysis using next-generation sequencing technology (NGS).
Our sequence analysis covers clinically important regions of each gene, including coding exons, +/- 10 base pairs of adjacent intronic sequence, and select noncoding variants. Our assay provides a Q30 quality-adjusted mean coverage depth of 350x (50x minimum, or supplemented with additional analysis). Variants classified as pathogenic or likely pathogenic are confirmed with orthogonal methods, except individual variants that have high quality scores and previously validated in at least ten unrelated samples.
Our analysis detects most intragenic deletions and duplications at single exon resolution. However, in rare situations, single-exon copy number events may not be analyzed due to inherent sequence properties or isolated reduction in data quality. If you are requesting the detection of a specific single-exon copy number variation, please contact Client Services before placing your order.
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