Moreover, it was found that the activity of PPT1 (which deficient activity is responsible for CLN1 – late infantile neuronal ceroid lipofuscinosis, LINCL) in peripheral blood leukocytes was found to be within the heterozygous state: 17 nmol/mg protein/hr (reference range: 53 + 18.6 nmol/mg protein/hr). This evidence concerns the gene PPT1 and neuronal ceroid lipofuscinosis.