Our results suggest a molecular mechanism underlying both the clinical similarities, as well as the disparities, between three developmental disorders, OS, caused by loss-of-function mutations in MID1 [20], GCPS, caused by loss-of-function in one GLI3 allele [11], [12], and PHS, caused by expression of truncated GLI3 due to premature stop codon formation [5], [13], [14]. The gene discussed is GLI3; the disease is Pallister-Hall syndrome.