A single gain of function missense mutation in CLCN6 has recently been shown to cause very severe disease in children (30) that would not be classed as NCL, although the mouse model lacking the function of the homologous gene causes mild lysosomal storage disease and the CLCN6 gene was considered a candidate gene for mild NCL disease (31). The gene discussed is CLCN6; the disease is neuronal ceroid lipofuscinosis.