Analysis of the molecular basis of neuronal migration in the mammalian CNS relies critically on the discovery and identification of genetic mutations that affect this process. Here, we report the detailed cerebellar phenotype caused by a new autosomal recessive neurological mouse mutation, scrambler (gene symbol scm). The scrambler mutation results in ataxic mice that exhibit several neuroanatomic defects reminiscent of reeler. The most obvious of these lies in the cerebellum, which is small and lacks foliation. Granule cells, although normally placed in an internal granule cell layer, are greatly reduced in number (�20 % of normal). Purkinje cells are also reduced in number, and the majority are located ectopically in deep cerebellar masses. There is a small population of Purkinje cells (�5 % of the total) that occupy a Purkinje cell layer between the molecular and granule cell layers. Despite this apparent disorganizatio
