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Test Catalog

Test ID: TPPTL    
Tripeptidyl Peptidase 1 (TPP1) and Palmitoyl-Protein Thioesterase 1 (PPT1), Leukocytes




An aid in the differential diagnosis of infantile and late infantile NCL


The neuronal ceroid lipofuscinoses (NCL) comprise a group of recessively inherited neurodegenerative disorders involved in lysosomal protein catabolism. Clinically they are characterized by vision loss, seizures, mental regression, behavioral changes, movement disorders, and the accumulation of storage material with a characteristic appearance by electron microscopy. Currently, at least 10 genetically distinct NCLs (CLN1-CLN10) are known. The age of onset and rate of deterioration varies according to type of NCL. Tissue damage is selective for the nervous system and many patients die in the first decade of life due to central nervous system degeneration. There is an overall incidence in the United States estimated at 1 in 12,500.


Children affected by infantile NCL (CLN1) typically have normal growth and development until about 6 to 12 months of age. Slowed head growth occurs at around 9 months followed by psychomotor degeneration, seizures, and progressive macular degeneration leading to blindness by the age of 2. CLN1 is caused by a deficiency of the lysosomal enzyme palmitoyl-protein thioesterase 1 (PPT1), which cleaves long-chain fatty acids (usually palmitate) from cysteine residues. Electron microscopy shows granular osmophilic deposits (GRODs) in most cell types. PPT1 is thought to play an active role in various cell processes including apoptosis, endocytosis, and lipid metabolism. Infantile NCL has an incidence of 1 in 20,000 in Finland and is rare elsewhere.




Diagnostic strategy depends on the age of onset of symptoms. In children presenting between the ages 0 to 4 years, enzyme assay of PPT1 and TPP1 is an appropriate first step. In addition, molecular genetic testing of CLN1 or CLN2 may allow for identification of the disease causing mutations.



85-326 nmol/hour/mg protein



20-93 nmol/hour/mg protein

Interpretation Provides information to assist in interpretation of the test results

Tripeptidyl peptidase 1 (TPP1) and palmitoyl-protein thioesterase 1 (PPT1) enzyme activity below 5 nmol/hour/mg of protein are highly suggestive of late-infantile and infantile neuronal ceroid lipofuscinoses, respectively.


This assay does not detect carrier status of neuronal ceroid lipofuscinoses.


Some variants with an age of onset occurring in older individuals have been noted.


1. Haltia M: The neuronal ceroid-lipofuscinoses: from past to present. Biochim Biophys Acta 2006;1762:850-856

2. Kavianen R: Juvenile-onset neuronal ceroid lipofuscinosis with infantile CLN1 mutation and palmitoyl-protein thioesterase deficiency. Eur J Neur 2007;14:369-372

