The evolutionarily conserved hedgehog (Hh) pathway is essential for organogenesis and plays critical roles in postnatal tissue maintenance and renewal. A unique feature of the vertebrate Hh pathway is that signal transduction requires the primary cilium (PC) where major pathway components are dynamically enriched. These factors include smoothened (SMO) and patched, which constitute the core reception system for sonic hedgehog (SHH) as well as GLI transcription factors, the key mediators of the pathway. Here, we report bi-allelic loss-of-function variations in SMO in seven individuals from five independent families; these variations cause a wide phenotypic spectrum of developmental anomalies affecting the brain (hypothalamic hamartoma and microcephaly), heart (atrioventricular septal defect), skeleton (postaxial polydactyly, narrow chest, and shortening of long bones), and enteric nervous system (aganglionosis). Cells derived from affected individuals showed normal ciliogenesis but severely altered Hh-signal transduction as a result of either altered PC trafficking or abnormal activation of the pathway downstream of SMO. In addition, Hh-independent GLI2 accumulation at the PC tip in cells from the affected individuals suggests a potential function of SMO in regulating basal ciliary trafficking of GLI2 when the pathway is off. Thus, loss of SMO function results in abnormal PC dynamics of key components of the Hh signaling pathway and leads to a large continuum of malformations in humans.

进化保守的刺猬（Hh）途径对于器官发生至关重要，并且在产后组织的维持和更新中起关键作用。脊椎动物Hh途径的独特之处在于信号转导需要初级纤毛（PC），其中主要的途径成分被动态富集。这些因素包括平滑（SMO）和斑驳，它们构成了声波刺猬（SHH）的核心接收系统，以及GLI转录因子（该途径的关键介体）。在这里，我们报告了SMO中的双等位基因功能丧失变异来自五个独立家庭的七个人；这些变化会导致广泛的表型异常，影响大脑（下丘脑错构瘤和小头畸形），心脏（房室间隔缺损），骨骼（后轴多指，狭窄的胸部和长骨的缩短）和肠神经系统（神经胶质瘤）。来自受影响个体的细胞显示出正常的纤毛发生，但由于PC转运的改变或SMO下游途径的异常激活而严重改变了Hh信号转导。另外，当受影响的细胞关闭时，来自受影响个体的细胞中PC末端的Hh非依赖性GLI2积累表明SMO在调节GLI2的基础睫状运输中具有潜在的功能。从而，