PDGFA and Spina bifida occulta: Spina bifida occulta with variable severity and penetrance has also been observed in Pdgfc−/−, Pdgfc−/−;PdgfaΔex6/Δex6, and Pdgfc−/−;Pdgfa+/− mice (Andrae et al., 2013; Ding et al., 2004), but not in single Pdgfa knockouts.