Leukoencephalopathy with vanishing white matter can be diagnosed on the basis of distinct clinical and magnetic resonance imaging (MRI) findings. It is a recessively inherited disorder, most often presenting in young children. The clinical symptoms include a slowly progressive cerebellar ataxia, spasticity, variable optic atrophy, and relatively preserved mental capacities. In addition, there are episodes of rapid and major deterioration following infections with fever and minor head trauma. These episodes can end in unexplained coma. MRI findings suggest that over time there is a progressive vanishing of the abnormal white matter, which is replaced by cerebrospinal fluid. We performed a genome-wide search and localized a gene for vanishing white matter on chromosome 3q27. We demonstrated that mutations in the gene EIF2B5 cause the disease. This gene encodes one of the five subunits of the translation factor eIF2B. Patients without mutations in the EIF2B5 gene were found to be mutated in one of the other genes that encode eIF2B subunits: EIF2B1 to EIF2B4.