Blood Spot Test May Aid Early Diagnosis of Infantile Batten Disease, Study Says

A new dried blood spot test may be a reliable and rapid method for obtaining an initial diagnosis of late infantile Batten disease, recent research shows.

The study, “Validity of a rapid and simple fluorometric tripeptidyl peptidase 1 (TPP1) assay using dried blood specimens to diagnose CLN2 disease,” was published in the journal Clinica Chimica Acta.

A timely diagnosis of late infantile Batten disease, also known as neuronal ceroid lipofuscinosis 2 (CLN2) disease, has become even more important now that the first enzyme replacement therapy (ERT) — BioMarin’s Brineura — has been approved for slowing disease progression.

According to researchers, this treatment can have a significant impact only if given early, before a significant destruction of brain tissue has occurred. As such, the inclusion of CLN2 disease into neonatal screening programs also is being discussed.

Researchers at the Center for Diagnostics and the NCL Clinic at the University Medical Center Eppendorf (UKE), Hamburg, Germany, collaborated to develop a rapid and convenient diagnostic test for CLN2 disease.

Their test is able to measure the activity of tripeptidyl peptidase 1 (TPP1) and palmitoyl protein thioesterase 1 (PPT1), the enzymes that are deficient in CLN2 and CLN1 disease.

The assay is performed on dried blood spots (DBS), an easy-to-do sampling method in which a small blood sample is blotted and dried on filter paper. After, it can be shipped for analysis by regular mail, if necessary. DBSs are widely used for newborn screening, where it is commonly known as the “heel prick test.”

The new assay employs a fluorescence-based method to quantify the levels of enzyme activity in DBSs.

In this study, researchers sought to test their assay’s reliability for detecting CLN2 disease in human samples.

They screened a large number of DBSs from patients suspected of having Batten disease, and seen at the UKE specialized NCL clinic over 12 years.

To be sure of the quality of the samples, the activity of two other enzymes, including PPT1 was included.

Among 3,883 DBSs assayed, 50 samples with lower-than-normal TPP1 activity were selected on the basis of good sample quality and sufficient clinical information of the patients.

All 50 patients identified by the test matched a clear diagnosis of CLN2 disease with documented symptoms of the disease and positive genetic testing for disease-causing mutations within TPP1 gene.

Of these, 43 patients had a classical manifestation of the disease with first symptoms appearing before the age of 4; seven had an atypical disease course, with later onset and slower neurological deterioration.

Although the sensitivity of the test could not be addressed by this study, researchers say “there is strong circumstantial evidence that the sensitivity is high.”

They contend that their institution (the NCL Clinic) is a major reference center for childhood degenerative diseases.

Over the 12-year period of this study the laboratory communicated normal results of TPP1 activity for more than 3,800 samples. So far, they have never learned of a patient who tested normal on the DBS test and was later diagnosed with CLN2 disease.

Moreover, they have no knowledge of contradictory results between their test and enzymatic studies in patient cells or genetic testing.

In light of these findings, researcher consider their test “a reliable, convenient and inexpensive tool for a first diagnostic step in suspected CLN2 disease.”

Moreover, because DBS sampling has been used widely to screen newborn babies for congenital diseases, the new test also can be modified to accommodate more neonatal screening of CLN2 disease, the team noted.

This and other approaches may become decisive for reaching a diagnosis and starting ERT early, with potentially better outcomes for patients.