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Paget’s disease from a genetic perspective
Bone Vol. 24, No. 5, Supplement May 1999:29S–30S
MOLECULAR GENETICS OF PAGET’S DISEASE
Paget’s Disease From a Genetic Perspective W. VAN HUL Department of Medical Genetics, University of Antwerp, Antwerp, Belgium
that is highly variable in number of repeats. Nowadays, any disease gene can be localized on the human genome by linkage analysis as long as the family data available is appropriate. In a second step of positional cloning, the disease gene needs to be isolated from the delineated candidate region. This involves mainly the construction of clone contigs spanning the candidate region and isolation of expressed sequences from these clones. The real disease gene can finally be identified from the remaining set of genes by mutation analysis in patients. The whole procedure has always been, and in many cases still is, a very arduous undertaking. However, genomic information nowadays accumulated into databases often significantly expedites the identification of a disease gene from a candidate region. Besides data obtained from genetic research worldwide, an extra impulse was given by the establishment of the Human Genome Project in 1991, an international project with the primary goal of sequencing the complete human genome by the year 2005. Also, initiatives have been taken to focus on the sequencing of expressed sequences and their mapping, resulting in a human gene map.1,10 In conclusion, during the last 10 years geneticists have been very successful in the identification of monogenic disease genes, but also tools have become available that can be used to identify genes involved in more complex multifactorial disorders. The identification of genes for this group of conditions is, because of their high prevalence and enormous socioeconomic impact, considered the major challenge.
Introduction In 1889, Sir James Paget wrote, “I have tried in vain to trace any hereditary tendency to the disease. I have not found it twice in the same family.” In the beginning of this century, however, the first families with more than one Paget patient were reported,13,16,21 and since then more than 50 familial cases have been described (OMIM). Several epidemiological studies confirmed the involvement of genetic factors in Paget’s disease. Despite this, even nowadays the precise role and contribution of genetic factors to the pathogenesis of Paget’s disease remains a matter of discussion and will only be solved by the identification of the predisposing genes and elucidation of the underlying pathogenic mechanisms. Identification of Disease Genes Two major approaches can be used for the cloning of a disease gene. The clinical features and biochemical characteristics of some disorders may suggest candidate aberrant proteins based on their function or expression. Purification of these gene products makes identification of the underlying gene possible. Because information about the function is used to identify the disease gene, this approach is called functional cloning.4,5 However, this has only worked for a few disorders, because, for the majority of genetic conditions, the link between the clinical features and the underlying gene defect cannot be made. During the last 15 years, a new and powerful strategy, referred to as positional cloning, has emerged, facilitating the localization and isolation of many genes of which no prior knowledge existed. Many important disease genes have been identified since then (cystic fibrosis, Duchenne muscular dystrophy, Huntington’s disease, breast and ovarian cancer, etc.). In a first step of this strategy the disease gene is localized on the human genome by linkage analysis. This implicates comparison of the segregation of the disease within families, with the segregation of different chromosomal regions. To follow the segregation of a chromosomal region through a pedigree, polymorphic DNA markers from that region are analyzed. These are sequences that are variable between individuals and therefore can be used as hallmarks to study the segregation of the chromosomal region to which they belong. The efficacy of linkage analysis relies mostly on the availability of large, multicase families and a set of precisely mapped, highly polymorphic DNA markers. For the latter, most credit must be given to the Ge´ne´thon laboratory in France, which constructed saturated genetic maps of microsatellite markers.7 These types of markers are highly polymorphic because they contain a small tandem repeat
Genetic Component in Paget’s Disease The presence of a genetic component in Paget’s disease is supported by several epidemiological studies and is therefore nowadays well recognized. In support of a genetic disease etiology is the ethnic difference in prevalence2 of the disease, which persists after migration to other countries.6,9 Sofaer et al.22 counted a tenfold increased prevalence among the parents and siblings of patients compared with these of spouses. Siris et al.20 found, for 12% of Paget’s disease patients, an affected firstdegree relative and calculated a sevenfold increased risk of developing Paget’s disease for a first-degree relative. In Spain, 40% of Paget’s disease patients were shown to have at least one affected first-degree relative.15 From these studies it is clear that Paget’s disease in general does not present as a monogenic disorder with a clear universal mode of inheritance. A multifactorial model with an environmental factor, like a virus infection affecting a genetically predisposed individual, is considered a reasonable hypothesis. Also, splitting of Paget’s disease into a “familial” form and a “sporadic” form with at least partially divergent pathogenic mechanisms may prove feasible. For “familial” Paget’s disease, different modes of inheritance have been suggested, but based on the families described so far an autosomal-dominant inheritence
Address for correspondence and reprints: Dr. Wim. Van Hul, Department of Medical Genetics, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium. © 1999 by Elsevier Science Inc. All rights reserved.
29S
8756-3282/99/$20.00 PII S8756-3282(99)00037-X
30S
W. Van Hul Molecular genetics of Paget’s disease
Bone Vol. 24, No. 5, Supplement May 1999:29S–30S
the chromosome 18p21-22 region (PDB2) previously associated with FEO. However, linkage to HLA could not be confirmed in recent linkage studies, and recent analysis of the PDB2 region in an extended set of families suggests that only a small percentage of familial Paget cases could be linked to PDB2. This illustrates that major breakthroughs still await. Extended studies are currently being undertaken both to clone the PDB2 gene on chromosome 18 and to localize the PDB3 gene on the human genome. With the currently available molecular genetic tools, one can be confident that this goal will be reached within the next few years. Therefore, ongoing molecular genetic studies promise to deliver, in the near future, major contributions toward further understanding the pathogenesis of Paget’s disease. References
Figure 1. Representation of loci suggested to be associated with Paget’s disease.
seems most likely. Although the prevalence of the disease is high, at least in some parts of the world, only a few multigeneration families have been found to be of suitable size for linkage studies. This could of course be a reflection of the fact that “familial” Paget’s disease represents only a small minority of Paget’s patients in general. However, two characteristics of the disease, the late age of onset and the high percentage of asymptomatic cases, are complicating factors in the identification of multicase families. Therefore, the incidence “familial” Paget’s disease may well be underestimated. Only the unraveling of the genetic mechanisms underlying Paget’s disease will elucidate whether “familial” and “sporadic” Paget’s disease states need to be considered different entities and, if so, in which proportion. Current Knowledge Suggestion for linkage with Paget’s disease was first obtained with the HLA locus on chromosome 6 (Figure 1) by Fotino et al.8 and Tilyard et al.23 This locus is now referred to as PDB1 (OMIM). However, this was not confirmed in the study by Moore and Hoffman14 and, in more recent extended linkage studies, suggests that the role of the HLA genes in the etiology of Paget’s disease is only minor, if at all. More recently, the PDB2 locus (OMIM) was assigned to chromosome 18q21-22.3,24 This region was analyzed because of the previous assignment to this region of the familial expansile osteolysis (FEO) disease gene,12 a rare autosomal-dominant disease with clinical similarities to Paget’s disease.18 It is hypothesized that Paget’s disease and FEO are allelic disorders caused by mutations in the same gene. The exclusion of both PDB1 and PDB2 in some extended Paget families11 illustrates the further genetic heterogeneity of Paget’s disease, and provides evidence for the existence of at least one other gene (PDB3) predisposing to Paget’s disease. Conclusion At present, two loci have been suggested to be linked to Paget’s disease: the HLA gene cluster on chromosome 6p (PDB1), and
1. Adams, M. D. and Kerlavage, A. R. et al. Initial assessment of human gene diversity and expression patterns based upon 83 million nucleotides of cDNA sequence. Nature 377(Suppl.):3S–174S; 1995. 2. Barker, D. J. The epidemiology of Paget’s disease of bone. Br Med Bull 40:396 – 400; 1984. 3. Cody, J. D. and Singer, F. R. et al. Genetic linkage of Paget’s disease of the bone to chromosome 18q. Am J Hum Genet 61:1117–1122; 1997. 4. Collins, F. S. Positional cloning: let’s not call it reverse anymore. Nature Genet 1:3– 6; 1992. 5. Collins, F. S. Positional cloning moves from perditional to traditional. Nature Genet 9:347–350; 1995. 6. Cundy, T., and McAnulty, K. et al. Evidence for secular change in Paget’s disease. Bone 20:69 –71; 1997. 7. Dib, C. and Faure´, S. et al. A comprehensive genetic map of the human genome based on 5,264 microsatellites. 380:152–154; 1996. 8. Fotino, M., Haymivits, A., and Falk, C. T. Evidence for linkage between HLA and Paget’s disease. Transplant Proc 9:1876 –1868; 1977. 9. Gardner, M. J., Guyer, P. B., and Barker, D. J. P. Radiological prevalence of Paget’s disease of bone in British migrants to Australia. Br Med J 1:1655– 1657; 1978. 10. Goodfellow, P. A big book of the human genome. Complementary endeavours. Nature 377:285–286; 1995. 11. Haslam, S. I., and Van Hul, W. et al. Paget’s disease of bone: evidence for a susceptibility locus on chromosome 18q and for genetic heterogeneity. J Bone Miner Res. In press. 12. Hughes, A. E., Shearman, A. M. et al. Genetic linkage of familial expansile osteolysis to chromosome 18q. Hum Molec Genet 3:359 –361; 1994. 13. Kilner, W. Two cases of osteitis deformans in one family. J. Lancet i1:221; 1904. 14. Moore, S. B., and Hoffman, D. L. Absence of HLA linkage in a family with osteitis deformans (Paget’s disease of bone). Tissue Antig 31:69 –70; 1988. 15. Morales-Piga, A. A., Rey-Rey, J. S. et al. Frequency and characteristics of familial aggregation of Paget’s disease of bone. J Bone Miner Res 10:663– 670; 1995. 16. Stahl B. F. Osteitis deformans, Paget’s disease, with reports of two cases and autopsy in one. Am J Med Sci 143:525; 1912. 17. Online Mendelian Inheritance in Man (OMIM). World Wide Web URL: http:// www.ncbi.nlm.nih.gov/omim/ 18. Osterberg, P. H., Wallace, R. G. H. et al. Familial expansile osteolysis. A new dysplasia. J Bone Jt Surg (Br) 70-B:255–260; 1988. 19. Paget, J. Remarks on osteitis deformans. Illus Med News 2:181; 1889. 20. Siris, E., Ottman, R. et al. Familial aggregation of Paget’s disease of bone. J Bone Miner Res 6:495–500; 1991. 21. Smith, S. M. A case of osteitis deformans in which the disease is present in father and son. Trans Med Soc Lond 28:324; 1905. 22. Sofaer, J. A., Holloway, S. M., and Emery, A. E. H. A family study of Paget’s disease of bone. J Epidemiol Commun Health 37:226 –231; 1983. 23. Tilyard, M. W. and Gardner, R. J. M. et al. A probable linkage between familial Paget’s disease and the HLA loci. Aust NZ J Med 12:498 –500; 1982. 24. Van Hul, W. and Haslam, S. I. et al. Genetic studies in familial Paget’s disease: suggestion for a susceptibility locus on chromosome 18 and for genetic heterogeneity. J Bone Miner Res 12(Suppl.):S179; 1997.
MOLECULAR GENETICS OF PAGET’S DISEASE
Paget’s Disease From a Genetic Perspective W. VAN HUL Department of Medical Genetics, University of Antwerp, Antwerp, Belgium
that is highly variable in number of repeats. Nowadays, any disease gene can be localized on the human genome by linkage analysis as long as the family data available is appropriate. In a second step of positional cloning, the disease gene needs to be isolated from the delineated candidate region. This involves mainly the construction of clone contigs spanning the candidate region and isolation of expressed sequences from these clones. The real disease gene can finally be identified from the remaining set of genes by mutation analysis in patients. The whole procedure has always been, and in many cases still is, a very arduous undertaking. However, genomic information nowadays accumulated into databases often significantly expedites the identification of a disease gene from a candidate region. Besides data obtained from genetic research worldwide, an extra impulse was given by the establishment of the Human Genome Project in 1991, an international project with the primary goal of sequencing the complete human genome by the year 2005. Also, initiatives have been taken to focus on the sequencing of expressed sequences and their mapping, resulting in a human gene map.1,10 In conclusion, during the last 10 years geneticists have been very successful in the identification of monogenic disease genes, but also tools have become available that can be used to identify genes involved in more complex multifactorial disorders. The identification of genes for this group of conditions is, because of their high prevalence and enormous socioeconomic impact, considered the major challenge.
Introduction In 1889, Sir James Paget wrote, “I have tried in vain to trace any hereditary tendency to the disease. I have not found it twice in the same family.” In the beginning of this century, however, the first families with more than one Paget patient were reported,13,16,21 and since then more than 50 familial cases have been described (OMIM). Several epidemiological studies confirmed the involvement of genetic factors in Paget’s disease. Despite this, even nowadays the precise role and contribution of genetic factors to the pathogenesis of Paget’s disease remains a matter of discussion and will only be solved by the identification of the predisposing genes and elucidation of the underlying pathogenic mechanisms. Identification of Disease Genes Two major approaches can be used for the cloning of a disease gene. The clinical features and biochemical characteristics of some disorders may suggest candidate aberrant proteins based on their function or expression. Purification of these gene products makes identification of the underlying gene possible. Because information about the function is used to identify the disease gene, this approach is called functional cloning.4,5 However, this has only worked for a few disorders, because, for the majority of genetic conditions, the link between the clinical features and the underlying gene defect cannot be made. During the last 15 years, a new and powerful strategy, referred to as positional cloning, has emerged, facilitating the localization and isolation of many genes of which no prior knowledge existed. Many important disease genes have been identified since then (cystic fibrosis, Duchenne muscular dystrophy, Huntington’s disease, breast and ovarian cancer, etc.). In a first step of this strategy the disease gene is localized on the human genome by linkage analysis. This implicates comparison of the segregation of the disease within families, with the segregation of different chromosomal regions. To follow the segregation of a chromosomal region through a pedigree, polymorphic DNA markers from that region are analyzed. These are sequences that are variable between individuals and therefore can be used as hallmarks to study the segregation of the chromosomal region to which they belong. The efficacy of linkage analysis relies mostly on the availability of large, multicase families and a set of precisely mapped, highly polymorphic DNA markers. For the latter, most credit must be given to the Ge´ne´thon laboratory in France, which constructed saturated genetic maps of microsatellite markers.7 These types of markers are highly polymorphic because they contain a small tandem repeat
Genetic Component in Paget’s Disease The presence of a genetic component in Paget’s disease is supported by several epidemiological studies and is therefore nowadays well recognized. In support of a genetic disease etiology is the ethnic difference in prevalence2 of the disease, which persists after migration to other countries.6,9 Sofaer et al.22 counted a tenfold increased prevalence among the parents and siblings of patients compared with these of spouses. Siris et al.20 found, for 12% of Paget’s disease patients, an affected firstdegree relative and calculated a sevenfold increased risk of developing Paget’s disease for a first-degree relative. In Spain, 40% of Paget’s disease patients were shown to have at least one affected first-degree relative.15 From these studies it is clear that Paget’s disease in general does not present as a monogenic disorder with a clear universal mode of inheritance. A multifactorial model with an environmental factor, like a virus infection affecting a genetically predisposed individual, is considered a reasonable hypothesis. Also, splitting of Paget’s disease into a “familial” form and a “sporadic” form with at least partially divergent pathogenic mechanisms may prove feasible. For “familial” Paget’s disease, different modes of inheritance have been suggested, but based on the families described so far an autosomal-dominant inheritence
Address for correspondence and reprints: Dr. Wim. Van Hul, Department of Medical Genetics, University of Antwerp, Universiteitsplein 1, 2610 Antwerp, Belgium. © 1999 by Elsevier Science Inc. All rights reserved.
29S
8756-3282/99/$20.00 PII S8756-3282(99)00037-X
30S
W. Van Hul Molecular genetics of Paget’s disease
Bone Vol. 24, No. 5, Supplement May 1999:29S–30S
the chromosome 18p21-22 region (PDB2) previously associated with FEO. However, linkage to HLA could not be confirmed in recent linkage studies, and recent analysis of the PDB2 region in an extended set of families suggests that only a small percentage of familial Paget cases could be linked to PDB2. This illustrates that major breakthroughs still await. Extended studies are currently being undertaken both to clone the PDB2 gene on chromosome 18 and to localize the PDB3 gene on the human genome. With the currently available molecular genetic tools, one can be confident that this goal will be reached within the next few years. Therefore, ongoing molecular genetic studies promise to deliver, in the near future, major contributions toward further understanding the pathogenesis of Paget’s disease. References
Figure 1. Representation of loci suggested to be associated with Paget’s disease.
seems most likely. Although the prevalence of the disease is high, at least in some parts of the world, only a few multigeneration families have been found to be of suitable size for linkage studies. This could of course be a reflection of the fact that “familial” Paget’s disease represents only a small minority of Paget’s patients in general. However, two characteristics of the disease, the late age of onset and the high percentage of asymptomatic cases, are complicating factors in the identification of multicase families. Therefore, the incidence “familial” Paget’s disease may well be underestimated. Only the unraveling of the genetic mechanisms underlying Paget’s disease will elucidate whether “familial” and “sporadic” Paget’s disease states need to be considered different entities and, if so, in which proportion. Current Knowledge Suggestion for linkage with Paget’s disease was first obtained with the HLA locus on chromosome 6 (Figure 1) by Fotino et al.8 and Tilyard et al.23 This locus is now referred to as PDB1 (OMIM). However, this was not confirmed in the study by Moore and Hoffman14 and, in more recent extended linkage studies, suggests that the role of the HLA genes in the etiology of Paget’s disease is only minor, if at all. More recently, the PDB2 locus (OMIM) was assigned to chromosome 18q21-22.3,24 This region was analyzed because of the previous assignment to this region of the familial expansile osteolysis (FEO) disease gene,12 a rare autosomal-dominant disease with clinical similarities to Paget’s disease.18 It is hypothesized that Paget’s disease and FEO are allelic disorders caused by mutations in the same gene. The exclusion of both PDB1 and PDB2 in some extended Paget families11 illustrates the further genetic heterogeneity of Paget’s disease, and provides evidence for the existence of at least one other gene (PDB3) predisposing to Paget’s disease. Conclusion At present, two loci have been suggested to be linked to Paget’s disease: the HLA gene cluster on chromosome 6p (PDB1), and
1. Adams, M. D. and Kerlavage, A. R. et al. Initial assessment of human gene diversity and expression patterns based upon 83 million nucleotides of cDNA sequence. Nature 377(Suppl.):3S–174S; 1995. 2. Barker, D. J. The epidemiology of Paget’s disease of bone. Br Med Bull 40:396 – 400; 1984. 3. Cody, J. D. and Singer, F. R. et al. Genetic linkage of Paget’s disease of the bone to chromosome 18q. Am J Hum Genet 61:1117–1122; 1997. 4. Collins, F. S. Positional cloning: let’s not call it reverse anymore. Nature Genet 1:3– 6; 1992. 5. Collins, F. S. Positional cloning moves from perditional to traditional. Nature Genet 9:347–350; 1995. 6. Cundy, T., and McAnulty, K. et al. Evidence for secular change in Paget’s disease. Bone 20:69 –71; 1997. 7. Dib, C. and Faure´, S. et al. A comprehensive genetic map of the human genome based on 5,264 microsatellites. 380:152–154; 1996. 8. Fotino, M., Haymivits, A., and Falk, C. T. Evidence for linkage between HLA and Paget’s disease. Transplant Proc 9:1876 –1868; 1977. 9. Gardner, M. J., Guyer, P. B., and Barker, D. J. P. Radiological prevalence of Paget’s disease of bone in British migrants to Australia. Br Med J 1:1655– 1657; 1978. 10. Goodfellow, P. A big book of the human genome. Complementary endeavours. Nature 377:285–286; 1995. 11. Haslam, S. I., and Van Hul, W. et al. Paget’s disease of bone: evidence for a susceptibility locus on chromosome 18q and for genetic heterogeneity. J Bone Miner Res. In press. 12. Hughes, A. E., Shearman, A. M. et al. Genetic linkage of familial expansile osteolysis to chromosome 18q. Hum Molec Genet 3:359 –361; 1994. 13. Kilner, W. Two cases of osteitis deformans in one family. J. Lancet i1:221; 1904. 14. Moore, S. B., and Hoffman, D. L. Absence of HLA linkage in a family with osteitis deformans (Paget’s disease of bone). Tissue Antig 31:69 –70; 1988. 15. Morales-Piga, A. A., Rey-Rey, J. S. et al. Frequency and characteristics of familial aggregation of Paget’s disease of bone. J Bone Miner Res 10:663– 670; 1995. 16. Stahl B. F. Osteitis deformans, Paget’s disease, with reports of two cases and autopsy in one. Am J Med Sci 143:525; 1912. 17. Online Mendelian Inheritance in Man (OMIM). World Wide Web URL: http:// www.ncbi.nlm.nih.gov/omim/ 18. Osterberg, P. H., Wallace, R. G. H. et al. Familial expansile osteolysis. A new dysplasia. J Bone Jt Surg (Br) 70-B:255–260; 1988. 19. Paget, J. Remarks on osteitis deformans. Illus Med News 2:181; 1889. 20. Siris, E., Ottman, R. et al. Familial aggregation of Paget’s disease of bone. J Bone Miner Res 6:495–500; 1991. 21. Smith, S. M. A case of osteitis deformans in which the disease is present in father and son. Trans Med Soc Lond 28:324; 1905. 22. Sofaer, J. A., Holloway, S. M., and Emery, A. E. H. A family study of Paget’s disease of bone. J Epidemiol Commun Health 37:226 –231; 1983. 23. Tilyard, M. W. and Gardner, R. J. M. et al. A probable linkage between familial Paget’s disease and the HLA loci. Aust NZ J Med 12:498 –500; 1982. 24. Van Hul, W. and Haslam, S. I. et al. Genetic studies in familial Paget’s disease: suggestion for a susceptibility locus on chromosome 18 and for genetic heterogeneity. J Bone Miner Res 12(Suppl.):S179; 1997.