TPP1 and neuronal ceroid lipofuscinosis 8: The most common forms of NCL are the “classical” infantile type, now called CLN1 disease and caused by mutations in PPT1, “classical” late-infantile form called CLN2 disease and due to mutations TPP1, and the “juvenile NCL,” or CLN3 disease caused by mutations in CLN3. Variant late-infantile forms include CLN5 (CLN5), CLN6 (CLN6), CLN7 (MFDS8), and CLN8 (CLN8) which are rarer than CLN1-3, but occur regularly, whereas the CLN10-CLN14 diseases are only reported occasionally.