Additionally, although some Mks1 mutant phenotypes (fusion and forking of the ribs, reduced mineralization in the skull and pulmonary hypoplasia) can easily be explained by a loss of Hh signaling, limb abnormalities reflect an expansion of Hh signaling, and the neural tube presents with phenotypes associated with both an expansion and reduction in Hh signaling (Weatherbee et al., 2009). This evidence concerns the gene MKS1 and Pulmonary hypoplasia.