Leukodystrophies are a group of orphan genetic diseases that primarily affect the white matter (WM) of the brain. The diagnosis and classification of these pathologies have been improved in the past decade thanks to the development of brain MRI, which allows the diagnosis of WM abnormalities in vivo and the continuous follow-up of patients. This article reviews recent advances made in leukodystrophy research by identifying causative genes. It focuses particularly on the genes involved in the hypomyelinated and vacuolating leukodystrophies, which provide new insights into the understanding of myelin formation and WM homeostasis.