Greig cephalopolysyndactyly syndrome (GCPS, MIM#175700) and isolated preaxial polydactyly type IV (PPD-IV, MIM#174700) are rare autosomal dominant disorders, both caused by mutations in the GLI3 zinc-finger transcription factor gene (Vortkamp et al. 1991). Here, GLI3 is linked to progressive pseudorheumatoid arthropathy of childhood.