Newborn screening for lysosomal storage disorders

Lysosomal storage disorders (LSD) represent a group of over 40 distinct genetic diseases with a total incidence of approximately 1:7,000 births. Bone marrow transplantation and enzyme replacement therapy are currently in use for the treatment of some disorders and new forms of enzyme and gene replacement therapy are actively being researched. The effectiveness of these therapies, particularly for the LSD involving the central nervous system and bone pathology, will rely heavily upon the early diagnosis and treatment of the disorder, before the onset of irreversible pathology. In the absence of a family history the only practical way to detect these disorders will be by a newborn screening program. One common feature of these disorders is an increase in the number and size of lysosomes within the cell from approximately 1% to as much as 50% of total cellular volume. Associated with this, is a corresponding increase in some lysosomal proteins. We propose that the measurement of one or more of these proteins in blood spots taken from Guthrie cards, will form the basis of a newborn screening program, for the detection of all LSD. We have identified a number of lysosomal proteins as potential markers for LSD. The level of these proteins has been determined in blood spots taken from Guthrie cards and in plasma samples from over 300 LSD affected individuals representing 25 disorders. Based on these results we have proposed a strategy for a newborn screening program involving a two tier system, utilizing time resolved fluorescence immunoquantification of the protein markers in the first tier, followed by tandem mass spectrometry for the determination of stored substrates in the second tier assays.