SMN1 and amyotrophic lateral sclerosis: The present study provides the evidence for the association of Shh-Gli1 regulation of Crabp1 expression with motor neuron differentiation, and that down-regulation of Crabp1, as well as the Shh-Gli signaling, is associated with motor neuron diseases in humans, such as ALS, SBMA, and SMA [17,28].