PTCH1 and Smith-Lemli-Opitz syndrome: Similarities in the phenotypes of humans with inherited disorders of sterol biosynthesis (Figure 1A, lathosterolosis and Smith-Lemli-Opitz syndrome [SLOS]) and the phenotypes seen with mutations in the Hh signalling pathway have led to the suggestion that cholesterol-synthesizing enzymes may somehow be involved in Ptch1-dependent Smo inhibition [1].