SHH and progressive pseudorheumatoid arthropathy of childhood: Currently, six loci have been identified in nonsyndromic PPD cases, including GLI1, GLI3, STKLD1, the zone of polarizing activity (ZPA) regulatory region (ZRS), which is a limb-specific enhancer of SHH that is located within intron five of LMBR1, the pre-ZRS region (a noncoding evolutionary conserved sequence 500 bp upstream of the ZRS), and a deletion located 240 kb from the SHH promotor.