Clonal status of fibrous dysplasia

The purpose of this study was to elucidate the clonality of fibrous dysplasia based on X-chromosome inactivation mosaicism and polymorphism in female somatic cells at the phosphoglycerate kinase (PGK) and androgen receptor (AR) loci using microdissection technology.

Nine patients with fibrous dysplasia were examined using clonality assays based on X-chromosome inactivation mosaicism. Lesions and surrounding soft tissues were microdissected from paraffin sections, and genomic DNA was extracted, pretreated with Hpa II or Hha I, and the PGK and AR genes were amplified by nested PCR. The single nucleotide polymorphism (SNP) at the PGK locus was identified by incubation with Bst XI and agarose gel electrophoresis. The CAG repeat length polymorphism at the AR locus was revealed on denaturing polyacrylamide gels and visualised by silver staining.

Microscopically, typical histological characteristics were seen in each sample. Lesions consisted of varying proportions of fibrous tissue and immature trabecular bone. Tissue consisted of collagenous fibres and fish-hook or comma-shaped trabecular bone without rows of cuboidal appositional osteoblasts on the surface. Restriction fragment length polymorphism (RFLP) of AR was found in seven of nine cases. The results of clonality assays demonstrated that seven cases of fibrous dysplasia were monoclonal, suggesting that they are neoplastic lesions.

We conclude that fibrous dysplasia may not be a hyperplastic lesion, but a neoplastic lesion. Additional studies with larger sample sizes will be needed to conclusively prove our hypothesis.