This document discusses lysosomal biomarkers for neuronal ceroid lipofuscinosis (NCL), a group of rare genetic disorders. The author identifies two key points: 1) Lysosomal changes can provide a rapid method to determine if treatments for NCLs are effective, as these diseases progress slowly and standard clinical methods make efficacy difficult to evaluate. 2) Studying lysosomal changes may provide insights into the functions of deficient NCL proteins and why their deficiency causes disease. The author has identified secondary alterations in lysosomal proteins in mouse models of three NCL types (CLN1, CLN2, CLN3) using mass spectrometry and aims to validate potential biomarkers in cerebrospinal fluid.