GREM1 , FRZB and DKK1 expression in healthy cartilage and osteoarthritic cartilage. Relative GREM1, FRZB and DKK1 mRNA expression levels of paired specimens of macroscopically preserved and degenerating osteoarthritic cartilage from a single osteoarthritic joint (n = 23) were assessed by quantitative PCR and were compared with healthy preadolescent (n = 4) and healthy adult (n = 3) articular cartilage specimen. Data expressed as fold-change relative to the specimen with the mRNA expression level on a log scale. *P <0.05. DKK1, dickkopf 1 homolog (Xenopus laevis); FRZB, frizzled-related protein; GADPH, glyceraldehyde 3-phosphate dehydrogenase; GREM1, Gremlin 1; OA, osteoarthritis.