PTCH1 and Mobius syndrome: Igf2 is already known to be required for MB development inthe Ptch+/- model as no tumours are observed in Igf2 null; Ptch+/- mice [50], over-expression of Igf2 in Ptch+/- mice increases the frequency of MBs generated by Shhtransfection of cerebellar neural progenitors [51], and at the cellular level Igf2 acts synergistically withShh to increases murine cGNP cell proliferation 10 fold [52].