Genetic neurometabolic diseases in childhood are multisystemic. Surprisingly, these genetic diseases can manifest for the first time during adolescence and adulthood. In this case, the clinical presentation and evolutivity are very different. In childhood, many neurological systems are touched and their evolution is rapidly lethal. In the adult, their presentation may be that of a degenerative disease of the central nervous system and, according to the disease, the syndrome is very particular and very systematized. From our clinical and biological experience, we would like to suggest a decision tree.