The classic early infantile onset NCL has a heterogeneous genetic background involving different genes, including PPT1 (lysosomal lipid hydrolase, MIM # 600722), CTSD (cathepsin D, lysosomal peptidase, MIM # 116840), and KCTD7 (a member of the KCTD gene family with a potassium channel tetramerization domain, MIM # 611725). The gene discussed is CTSD; the disease is neuronal ceroid lipofuscinosis.