Human Genetics

, Volume 117, Issue 1, pp 43–53 | Cite as

A homozygous nonsense mutation in SOX9 in the dominant disorder campomelic dysplasia: a case of mitotic gene conversion

  • Ramona Pop
  • Michael V. Zaragoza
  • Mara Gaudette
  • Ulrike Dohrmann
  • Gerd SchererEmail author
Original Investigation


Campomelic dysplasia (CD; MIM 114290), an autosomal dominant skeletal malformation syndrome with XY sex reversal, is caused by heterozygous de novo mutations in and around the SOX9 gene on 17q. We report a patient with typical signs of CD, including sex reversal, who was, surprisingly, homozygous for the nonsense mutation Y440X. Since neither parent carried the Y440X mutation, possible mechanisms explaining the homozygous situation were a de novo mutation followed by uniparental isodisomy, somatic crossing over, or gene conversion. As the patient was heterozygous for six microsatellite markers flanking SOX9, uniparental isodisomy and somatic crossing over were excluded. Analysis of intragenic single-nucleotide polymorphisms suggested that the homozygous mutation arose by a mitotic gene conversion event involving exchange of at least 440 nucleotides and at most 2,208 nucleotides between a de novo mutant maternal allele and a wild-type paternal allele. Analysis of cloned alleles showed that homozygous mutant cells constituted about 80% of the leukocyte cell population of the patient, whereas about 20% were heterozygous mutant cells. Heterozygous Y440X mutations, previously described in three CD cases, have been identified in seven additional cases, thus constituting the most frequent recurrent mutations in SOX9. These patients frequently have a milder phenotype with longer survival, possibly because of the retention of some transactivation activity of the mutant protein on SOX9 target genes, as shown by cell transfection experiments. The fact that the patient survived for 3 months may thus be explained by homozygosity for a hypomorphic rather than a complete loss-of-function allele, in combination with somatic mosaicism. This is, to our knowledge, the first report of mitotic gene conversion of a wild-type allele by a de novo mutant allele in humans.


Gene Conversion Clubfoot Homozygous Mutation SOX9 Gene Somatic Mosaicism 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We thank the parents of the patient for their interest and support, Maureen Bocian for providing information about the AG family, Victor Steimle for access to and help with the LightCycler, and Michael Wegner for the Neuro2A cell line. We are grateful to Drs. Mary Ann Floyd, Ephrat Levy-Lahad, Joan Paterson, Elie Picard, Rosário Santos, Eva Seemanová, Niels Tommerup, and William Wilcox for submitting samples of and providing information on patients with heterozygous Y440X mutations, and to Maureen Bocian and Jürgen Kohlhase for comments on the manuscript. We appreciate the constructive comments made by one of the reviewers. Francis Poulat, L. Bridgewater, and Benoit de Crombrugghe are acknowledged for providing plasmids. This work was supported by a grant from the Deutsche Forschungsgemeinschaft to G.S. (Sche 194/15–1 and –2).


  1. Akiyama H, Chaboissier MC, Martin JF, Schedl A, Crombrugghe B de (2002) The transcription factor Sox9 has essential roles in successive steps of the chondrocyte differentiation pathway and is required for expression of Sox5 and Sox6. Genes Dev 16:2813–2828CrossRefGoogle Scholar
  2. Arango NA, Lovell-Badge R, Behringer RR (1999) Targeted mutagenesis of the endogenous mouse Mis gene promoter: in vivo definition of genetic pathways of vertebrate sexual development. Cell 99:409–419Google Scholar
  3. Bentley DL, Rabbits TH (1983) Evolution of immunoglobulin V genes: evidence indicating that recently duplicated human Vκ sequences have diverged by gene conversion. Cell 32:181–189Google Scholar
  4. Bernard P, Tang P, Liu S, Dewing P, Harley VR, Vilain E (2003) Dimerization of SOX9 is required for chondrogenesis, but not for sex determination. Hum Mol Genet 12:1755–1765Google Scholar
  5. Bi W, Deng JM, Zhang Z, Behringer RB, Crombrugghe B de (1999) Sox9 is required for cartilage formation. Nat Genet 22:85–89Google Scholar
  6. Bottema CDK, Bottema MJ, Ketterling RP, Yoon HS, Janco RL, Phillips JA III, Sommer SS (1991) Why does the human factor IX gene have a G + C content of 40%? Am J Hum Genet 49:839–850Google Scholar
  7. Bridgewater LC, Lefebvre V, Crombrugghe B de (1998) Chondrocyte-specific enhancer elements in the Col11a2 gene resemble the Col2a1 tissue-specific enhancer. J Biol Chem 273:14998–15006Google Scholar
  8. Bridgewater LC, Walker MD, Miller GC, Ellison TA, Holsinger LD, Potter JL, Jackson TL, Chen RK, Winkel VL, Zhang Z, McKinney S, Crombrugghe B de (2003) Adjacent DNA sequences modulate Sox9 transcriptional activation at paired Sox sites in three chondrocyte-specific enhancer elements. Nucleic Acids Res 31:1541–1553Google Scholar
  9. Cavenee WK, Dryja TP, Phillips RA, Benedict WF, Godbout R, Gallie BL, Murphree AL, Strong LC, White RL (1993) Expression of recessive alleles by chromosomal mechanisms in retinoblastoma. Nature 305:779–784Google Scholar
  10. Chaboissier MC, Kobayashi A, Vidal VIP, Lützkendorf S, Kant HJK van de, Wegner M, Rooij DG de, Behringer RR, Schedl A (2004) Functional analysis of Sox8 and Sox9 during sex determination in the mouse. Development 131:1891–1901Google Scholar
  11. Collier S, Tassabehji M, Sinnott P, Strachan T (1993) A de novo pathological point mutation at the 21-hydroxylase locus: implications for gene conversion in the human genome. Nat Genet 3:260–265Google Scholar
  12. Cooper DN, Youssouffian H (1988) The CpG dinucleotide and human genetic disease. Hum Genet 78:151–155CrossRefPubMedGoogle Scholar
  13. Eikenboom JCJ, Vink T, Briet E, Sixma JJ, Reitsma PH (1994) Multiple substitutions in the von Willebrand factor gene that mimic the pseudogene sequence. Proc Natl Acad Sci USA 91:2221–2224Google Scholar
  14. Fearon ER, Winkelstein JA, Civin CI, Pardoll DM, Vogelstein B (1987) Carrier detection in X-linked agammaglobulinemia by analysis of X-chromosome inactivation. N Engl J Med 316:427–431Google Scholar
  15. Foster JW, Dominguez-Steglich MA, Guioli S, Kwok C, Weller PA, Stevanovic M, Weissenbach J, Mansour S, Young ID, Goodfellow PN, Brook JD, Schafer AJ (1994) Campomelic dysplasia and autosomal sex reversal caused by mutations in an SRY-related gene. Nature 372:525–530Google Scholar
  16. Hageman RM, Cameron FJ, Sinclair AH (1998) Mutation analysis of the SOX9 gene in a patient with campomelic dysplasia. Hum Mutat Suppl 1:S112–S113Google Scholar
  17. Hirschhorn R (2003) In vivo reversion to normal of inherited mutations in humans. J Med Genet 40:721–728Google Scholar
  18. Houston CS, Opitz JM, Spranger JW, Macpherson RI, Reed MH, Gilbert EF, Herrmann J, Schinzel A (1983) The campomelic syndrome: review, report of 17 cases, and follow-up on the currently 17-year-old boy first reported by Maroteaux et al. in 1971. Am J Med Genet 15:3–28Google Scholar
  19. Johnson RD, Jasin M (2001) Double-strand-break-induced homologous recombination in mammalian cells. Biochem Soc Trans 29:196–201CrossRefGoogle Scholar
  20. Jonkman MF, Scheffer H, Stulp R, Pas HH, Nijenhuis M, Heeres K, Owaribe K, Pulkkinen L, Uitto J (1997) Revertant mosaicism in epidermolysis bullosa caused by mitotic gene conversion. Cell 88:543–551CrossRefPubMedGoogle Scholar
  21. Kent J, Wheatley SC, Andrews JE, Sinclair AH, Koopman P (1996) A male-specific role for SOX9 in vertebrate sex determination. Development 122:2813–2822Google Scholar
  22. Kourilsky P (1986) Molecular mechanisms for gene conversion in higher cells. Trends Genet 2:60–63Google Scholar
  23. Kuhner MK, Lawlor DA, Ennis PD, Parham P (1991) Gene conversion in the evolution of the human and chimpanzee MHC class I loci. Tissue Antigens 38:152–164Google Scholar
  24. Lefebvre V, Huang W, Harley VR, Goodfellow PN, Crombrugghe B de (1997) SOX9 is a potent activator of the chondrocyte-specific enhancer of the pro alpha1(II) collagen gene. Mol Cell Biol 17:2336–1246Google Scholar
  25. Mansour S, Hall CM, Pembrey ME, Young ID (1995) A clinical and genetic study of campomelic dysplasia. J Med Genet 32:415–420Google Scholar
  26. McDowall S, Argentaro A, Ranganathan S, Weller P, Mertin S, Mansour S, Tolmie J, Harley V (1999) Functional and structural studies of wild type SOX9 and mutations causing campomelic dysplasia. J Biol Chem 274:24023–24030Google Scholar
  27. Meyer J, Südbeck P, Held M, Wagner T, Schmitz ML, Bricarelli FD, Eggermont E, Friedrich U, Haas OA, Kobelt A, Leroy JG, Maldergem L van, Michel E, Mitulla B, Pfeiffer RA, Schinzel A, Schmidt H, Scherer G (1997) Mutational analysis of the SOX9 gene in campomelic dysplasia and autosomal sex reversal: lack of genotype/phenotype correlations. Hum Mol Genet 6:91–98Google Scholar
  28. Morais da Silva S, Hacker A, Harley V, Goodfellow P, Swain A, Lovell-Badge R (1996) Sox9 expression during gonadal development implies a conserved role for the gene in testis differentiation in mammals and birds. Nat Genet 14:62–68Google Scholar
  29. Ng LJ, Wheatley S, Muscat GEO, Conway-Campbell J, Bowles J, Wright E, Bell DM, Tam PP, Cheah KS, Koopman P (1997) SOX9 binds DNA, activates transcription, and coexpresses with type II collagen during chondrogenesis in the mouse. Dev Biol 183:108–121CrossRefPubMedGoogle Scholar
  30. Olney PN, Kean LS, Graham D, Elsas LJ, May KM (1999) Campomelic syndrome and deletion of SOX9. Am J Med Genet 84:20–24Google Scholar
  31. Pfeifer D, Kist R, Dewar K, Devon K, Lander ES, Birren B, Korniszewski L, Back E, Scherer G (1999) Campomelic dysplasia translocation breakpoints are scattered over 1 Mb proximal to SOX9: evidence for an extended control region. Am J Hum Genet 65:111–124Google Scholar
  32. Pop R, Conz C, Lindenberg KS, Blesson S, Schmalenberger B, Briault S, Pfeifer D, Scherer G (2004) Screening of the 1 Mb SOX9 5′ control region by array CGH identifies a large deletion in a case of campomelic dysplasia with XY sex reversal. J Med Genet 41:e47Google Scholar
  33. Reyniers E, Thienen MN van, Meire F, Boulle K de, Devries K, Kestelijn P, Willems PJ (1995) Gene conversion between red and defective green opsin gene in blue cone monochromacy. Genomics 29:323–328Google Scholar
  34. Santa Barbara P de, Bonneaud N, Boizet B, Desclozeaux M, Moniot B, Südbeck P, Scherer G, Poulat F, Berta P (1998) Direct interaction of SRY-related protein SOX9 and steroidogenic factor 1 regulates transcription of the human anti-Müllerian hormone gene. Mol Cell Biol 18:6653–6665Google Scholar
  35. Slightom JL, Blechl AE, Smithies O (1980) Human fetal Gγ- and Aγ-globin genes: complete nucleotide sequences suggest that DNA can be exchanged between these duplicate genes. Cell 21:627–638Google Scholar
  36. Sock E, Pagon RA, Keymolen K, Lissens W, Wegner M, Scherer G (2003) Loss of DNA-dependent dimerization of the transcription factor SOX9 as a cause for campomelic dysplasia. Hum Mol Genet 12:1439–1447Google Scholar
  37. Südbeck P, Schmitz ML, Baeuerle PA, Scherer G (1996) Sex reversal by loss of the C-terminal transactivation domain of human SOX9. Nat Genet 13:230–232Google Scholar
  38. Vidal VP, Chaboissier MC, Rooij DG de, Schedl A (2001) Sox9 induces testis development in XX transgenic mice. Nat Genet 28:216–217Google Scholar
  39. Wagner T, Wirth J, Meyer J, Zabel B, Held M, Zimmer J, Pasantes J, Dagna Bricarelli F, Keutel J, Hustert E, Wolf U, Tommerup N, Schempp W, Scherer G (1994) Autosomal sex reversal and campomelic dysplasia are caused by mutations in and around the SRY-related gene SOX9. Cell 79:1111–1120Google Scholar
  40. Watnick TJ, Gandolph MA, Weber H, Neumann HPH, Germino GG (1998) Gene conversion is a likely cause of mutation in PKD1. Hum Mol Genet 7:1239–1243Google Scholar
  41. Wiese C, Pierce AJ, Gauny SS, Jasin M, Kronenberg A (2002) Gene conversion is strongly induced in human cells by double-strand breaks and is modulated by the expression of BCL-x(L). Cancer Res 62:1279–1283Google Scholar

Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Ramona Pop
    • 1
    • 2
    • 4
    • 4
  • Michael V. Zaragoza
    • 3
  • Mara Gaudette
    • 3
  • Ulrike Dohrmann
    • 1
  • Gerd Scherer
    • 1
  1. 1.Institute of Human Genetics and AnthropologyUniversity of FreiburgFreiburgGermany
  2. 2.Faculty for BiologyUniversity of FreiburgFreiburgGermany
  3. 3.Division of Human Genetics, Department of PediatricsUniversity of California IrvineOrangeUSA
  4. 4.Division of Hematology/Oncology, Department of Cancer Biology/PediatricsUniversity of Massachusetts Medical SchoolWorcesterUSA

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