CLN2 disease, also known as NCL2 or late infantile neuronal ceroid lipofuscinosis, is a very rare, progressive neurodegenerative metabolic disease. It is caused by mutations in the TPP1 gene, as a result of which an important enzyme is missing. The disease usually begins between the ages of 2 and 4. Typical features are epilepsy, loss of acquired skills, movement disorders, visual impairment up to blindness and a shortened life expectancy.