A new study reports on the development of a novel dried blood spot (DBS) enzyme activity assay to stratify patients with lysosomal acid lipase deficiency (LAL-D) into those with Wolman disease and those with the less severe cholesteryl ester storage disease (CESD).

The assay, reported on in Molecular Genetics and Metabolism Reports, uses a highly specific LAL substrate that correlates biochemical and clinical phenotypes, which the previous nonspecific substrate could not demonstrate.

“Traditionally, LAL activity is measured in DBS with a non-specific fluorogenic substrate in the presence and absence of lalistat 2, a specific LAL inhibitor,” the authors wrote. “More recently, a highly specific LAL substrate, 4-propyl-8-methyl-7-hydroxycoumarin [P-PMHC], was developed in our laboratory and the assay can be analyzed by either ultra-performance liquid chromatography tandem mass spectrometry or fluorometry.”


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The traditional diagnostic method requires two incubations per sample, which can be cumbersome, and its LAL activity measurement is not very precise. Thus, while the diagnostic accuracy is excellent, it cannot predict disease severity.

Read more about LAL-D testing

The authors used the new P-PMHC assay to measure LAL activity in DBS from patients and carriers with LAL-D and observed 60-fold lower enzyme activity in patients than in LAL-D carriers. Furthermore, they discovered they could also distinguish between those with Wolman disease and CESD based on residual enzyme activity levels.

The authors note that stratification of patients with LAL-D has significant implications for initially asymptomatic newborn screening and for patient management. Given that genotyping is useful but can be inconclusive, the new assay provides complementary biochemical information to inform the diagnosis and prognosis.

The authors caution that storage conditions for the newborn DBS was not ideal, limiting their ability to accurately assess enzyme activity, and that the DBS samples were not age-matched between the patients and controls. A prospective pilot study using the new assay is currently ongoing in New York and should provide more data on the validity of this new approach to LAL-D screening.

Reference

Hong X, Chen Y, Barr M, et al. Stratification of patients with lysosomal acid lipase deficiency by enzyme activity in dried blood spots. Mol Gen Metab Rep. Published online November 10, 2022. doi:10.1016/j.ymgmr.2022.100935