Neuropathological characterization of various non-AP-4-related spastic paraplegias has previously identified cerebellar abnormalities in a number of complex HSP subtypes.4,32,33 Histopathological examination of the cerebellar region of Ap4b1 (−/−) mice did not show any major pathological abnormalities such as atrophy, severe neuronal loss or Purkinje cell loss and the cerebellum appeared morphologically normal compared with WT mice. Here, AP4B1 is linked to Spastic paraplegia.