In our study, flow cytometry allowed us to uncover that LAMP‐1 expression was most pronounced in CD4 and CD8 positive cells (T‐cells) in severe end CLN3 disease while at the mildest end of the disease spectrum, in CLN3‐associated retinal degeneration, LAMP‐1 expression was almost absent in T‐cells while pronounced in CD20 positive cells (B‐cells). The gene discussed is LAMP1; the disease is retinal degeneration.