TPP1 and neuronal ceroid lipofuscinosis: A study by Lojewski and co-workers in 2014 generated the first NCL iPSCs, using fibroblasts derived from two patients with late-infantile NCL linked to mutations in TPP1 (tripeptidyl peptidase 1), and four patients with juvenile NCL and mutations in CLN3. TPP1 encodes a member of the sedolisin family of serine proteases and CLN3 encodes a protein involved in lysosomal function.