Juvenile neuronal ceroid lipofuscinosis (Batten disease) is a neurodegenerative 
disorder caused by defective function of the lysosomal membrane glycoprotein 
CLN3. The activity of the lysosomal acid phosphatase (LAP/ACP2) was found to be 
significantly increased in the cerebellum and brain stem of Cln3-targeted mice 
during the early stages of postnatal life. Histochemical localization studies 
revealed an increased LAP/ACP2 staining intensity in neurons of the cerebral 
cortex of 48-week-old Cln3-targeted mice as compared with controls. 
Additionally, the expression of another lysosomal membrane protein LAMP-2 was 
increased in all brain areas. Knockdown of CLN3 expression in HeLa cells by RNA 
interference also resulted in increased LAP/ACP2 and LAMP-2 expression. Finally 
in fibroblasts of two juvenile neuronal ceroid lipofuscinosis patients elevated 
levels of LAP/ACP2 were found. Both activation of gene transcription and 
increased protein half-life appear to contribute to increased LAP/ACP2 protein 
expression in CLN3-deficient cells. The data suggest that lysosomal dysfunction 
and accumulation of storage material require increased biogenesis of LAP/ACP2 
and LAMP-2 positive membranes which makes LAP/ACP2 suitable as biomarker of 
Batten disease.