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Genotype-Phenotype Correlations, Response to Bisphosphonate Treatment and Pharmaco-genetics in 150 Swedish Families with Osteogenesis Imperfecta (Type I, IV and III)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Metabolic Bone Diseases. (Metabola bensjukdomar)
Karolinska Institutet.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Metabolic Bone Diseases. Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology.
Karolinska Institutet.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Introduction: Osteogenesis imperfecta (OI) is a rare heterogeneous disorder leading to bone fragility, spanning from mild to lethal in severity. Over 1500 mutations have been described in collagen type I, encoded by COL1A1 and COL1A2. Bisphosphonate treatment is standard of care and published studies clearly show beneficial effects on Bone Mineral Density (BMD) and vertebral geometry. However, information on BMD increase in relation to age and BMD at onset is limited and there are few studies on influence of mutation type on treatment response. In this study Swedish patients with OI types I, IV and III were investigated with respect to genotype-phenotype correlations, BMD response on bisphosphonate treatment, and pharmaco-genetics.

Materials and Methods: 150 families (202 individuals) with OI participated: 137 type I, 40 type IV and 25 type III. Data on phenotype and bisphosphonate treatment were collected and sequencing of COL1A1 and COL1A2 performed.

Results: In 119 families a mutation was detected; in COL1A1 52 quantitative and 35 qualitative mutations were found and in COL1A2 32 qualitative mutations were found. Several unrelated individuals were found to harbor mutations with the same positions and substitutions and only 15 qualitative mutations were novel, supporting the idea of mutational hotspots. Genotype-phenotype analysis confirmed that mutations situated in the a1-chain are associated with a more severe phenotype, blue sclerae are strongly associated with COL1A1 null alleles, qualitative mutations are associated with DI, and for qualitative mutations position relative to N- and C-terminal is correlated to phenotype. A few novel mutations with unconventional locations were found.

Bisphosphonate treatment response was inversely correlated with age (p=<0.0001) and lumbar spine BMD at onset (p=0.006). Mutations associated with a more severe phenotype had an improved response to treatment when analyzing 2-year delta lumbar spine Z-score values; mutations in COL1A1 vs. COL1A2 (p=0.03), qualitative mutations in COL1A1 vs. COL1A2 (p=0.006), serine substitutions in COL1A1 vs. COL1A2 (p=0.007) and qualitative vs. qualitative mutations in COL1A1 (p=0.02) all exhibited this pattern. Bisphosphonate response was not correlated to either OI type or gender.

Conclusions: The genotype-phenotype correlations described here confirm previous reports of influence of chain affected, intrachain location, and mutation type on phenotype. BMD response to bisphosphonate treatment is inversely related to age and BMD at onset. Pharmaco-genetic analyses show an increased response to bisphosphonate treatment for more severe mutations types. This effect is attenuated over time.

Keyword [en]
Osteogenesis imperfecta, OI, Bisphosphonate, Therapy, Genotype, Phenotype, Parmaco-genetics, Mutation
National Category
Endocrinology and Diabetes
Research subject
Medical Genetics; Genetics; Medicine
URN: urn:nbn:se:uu:diva-208940OAI: oai:DiVA.org:uu-208940DiVA: diva2:655410
Available from: 2013-10-11 Created: 2013-10-11 Last updated: 2013-12-05
In thesis
1. Osteogenesis Imperfecta: Genetic and Therapeutic Studies
Open this publication in new window or tab >>Osteogenesis Imperfecta: Genetic and Therapeutic Studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Osteogenesis imperfecta (OI) is a heterogeneous disease of connective tissue, the cardinal symptom being fractures and severity ranging from mild to lethal. Dominant mutations in collagen I, encoded by COL1A1 and COL1A2, cause >90% of cases.

To delineate genotype-phenotype correlations and pharmaco-genetic response, collagen I was sequenced in 150 unrelated Swedish families and clinical data were collected in Paper I. Mutation type, gene affected, and N- to C-terminal location correlated with phenotype and severity. Bisphosphonate response assessed by calculated yearly change in lumbar spine bone mineral density (BMD) was inversely related to age and BMD at treatment initiation. Mutations associated with a more severe phenotype exhibited an increased response after 2 years; however, all types of OI responded well.

To investigate the effect of naturally occurring variations in collagen I, the only common coding single nucleotide polymorphism (rs42524 in COL1A2) was genotyped in 2004 healthy men in Paper II. Heterozygous genotype was associated with decreased BMD and an increased risk of stroke.

An adolescent with repeated fractures despite a markedly high BMD harbored a unique C-terminal procollagen cleavage-site mutation in COL1A1, which motivated extensive investigations in concert with a similar COL1A2 case in Paper III. The probands were found to have impaired procollagen processing, incorporation of collagen with retained C-propeptide in matrix and increased mineral to matrix ratio, which demonstrates that C-propeptide cleavage is crucial to normal bone mineralization and structure.

Bisphosphonate therapy has insufficient effect in OI, and as classical OI is a dominant disorder severe cases would benefit from silencing of the mutated allele. In Paper IV and V small interfering RNAs (siRNAs) were used to allele-specifically target primary human bone cells heterozygous for I) a coding polymorphism in COL1A2 and II) insertion/deletions in the 3’UTR of COL1A1 and COL1A2. Results were promising with altered allele ratios and decreased mRNA levels in the predicted fashion.

To summarize, this thesis found that collagen I is crucial to bone and connective tissue and that collagen I mutations create markedly diverse phenotypes. Age, BMD and pharmaco-genetic effects influence the response to bisphosphonate therapy in individuals with OI; however, novel approaches are needed. Utilizing allele-specific siRNAs may be a way forward in the treatment of severe OI.


Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 96 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 936
OI, BMD, Genotype, Phenotype, Pharmaco-genetics, Bisphosphonate, Therapy, Gene-therapy, Mutation, Collagen, Collagen type I, Allele-specific silencing, siRNA, RNAi, COL1A1, COL1A2, Stroke, C-propeptide, Mineralization, Heterozygous disadvantage
National Category
Endocrinology and Diabetes
Research subject
Genetics; Medicine; Medical Genetics
urn:nbn:se:uu:diva-208942 (URN)978-91-554-8772-0 (ISBN)
Public defence
2013-11-29, Enghoffsalen, Ingång 50, Akademiska Sjukhuset, Uppsala, 09:15 (English)
Swedish Research Council
Available from: 2013-11-08 Created: 2013-10-11 Last updated: 2014-01-23

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