Macrostomia, (horizontal facial cleft, lateral facial cleft, transversefacialcleft)isararecongenitalmalformation.Onoccasion,itcanbea sign in certain syndromes, such as Goldenhar syndrome orTreacher–Collin syndrome [McCarthy and West, 1977]. Rarely,it occurs as an isolated malformation. The cause has remainedunknown.We studied autosomal dominantly inherited macrosomia in alarge family of Chinese Han origin (Fig. 1A and Table I). Linkageandhaplotypeanalysisidentifiedthemacrostomia-associatedlocusbetween markers D1S193 and D1S2652 on 1p32–1p34; the maxi-mum LOD score at D1S2797 was 4.18 (q¼0.00, Table II). At thislocus, we identified a heterozygous mutation in exon 11(NC_000001.9) of PTCH2 (1423G!A, resulting in Val471Ile inthe 4th transmembrane domain) (NP_003729) in all patients withmacrosomia (Fig. 1B). No mutation was found in family memberswholackedmacrosomiaandwefoundnoPTCH2mutationsin520unrelated controls.Although over-expression of SMO induced GLI-dependentluciferase activity, co-expression of wild-type PTCH2 inhibitedSMO-induced activity significantly, confirming the inhibitoryfunction of PTCH2 in the SHH signaling network (Fig. 1C). Incontrast, co-expression of PTCH2 Val471Ile did not inhibit SMO-inducedluciferaseactivity.Over-expressionofPTCH2significantlyinhibited cell proliferation, but over-expression of PTCH2 Va-l471Ile did not appear to have a major effect on the cell growth rate(Fig. 1D). Western blot analysis confirmed that the expression levelof PTCH2 and PTCH2 Val471Ile is similar (Fig. 1E).The hedgehog signaling network has been reviewed extensivelyelsewhere [Cohen, 2003]. PTCH2 encodes a 1204-amino acidtransmembrane protein with about a 54% overall identity toPTCH1 [Motoyama et al., 1998; Smyth et al., 1999] and a 90%identity to Ptch2 in mice [Carpenter et al., 1998]. In the absence ofSonic Hedgehog (SHH) stimulation, PTCH2, like PTCH1, canmaintain the hedgehog signaling pathway in an inactive state byinhibiting SMO. When SHH binds to PTCH2, the inhibitory effectof PTCH2 on SMO is removed, resulting in activation of SMO,downstreamsignaling,andupregulationoftargetgenes,suchastheGLI family proteins [Hahn et al., 1996; Young et al., 2000; Chenetal., 2002;Vokesand McMahon, 2004;Hutchinetal.,2005]. SHH