Integrated Multianalyte Second-Tier Testing for Newborn Screening for MSUD, IVA, and GAMT Deficiencies

Abstract Advances in mass spectrometry have allowed for expansion of newborn screening test panels over the last decade but with increased numbers of disorders have come increased concerns with false-positive rates. The introduction of second-tier testing has improved the specificity of screening for a number of disorders without any corresponding sacrifice in sensitivity. Such testing does, however, put pressure on scarce laboratory resources including instrument and personnel time and even the bloodspot sample itself. The British Columbia Newborn Screening Program has developed an integrated second-tier screening approach to improve test performance without the requirement to resample and reprocess the original bloodspot specimen. By utilizing the residual extract from the first-tier assay and introducing a chromatography step as the second tier, we have been able to reduce false-positive rates due to interfering isobaric compounds for 3 different disorders (maple syrup urine disease, isovaleric aciduria, and guanidinoacetate methyltransferase) in a single multianalyte assay.

Generation of a conditional knockout of murine glucocerebrosidase: utility for the study of Gaucher disease.

Gaucher disease is a disorder of sphingolipid metabolism resulting from an inherited deficiency of the lysosomal hydrolase glucocerebrosidase. Affected individuals present with a spectrum of clinical symptoms ranging from hepatosplenomegaly, haematological abnormalities, and bone pain in type 1 disease, to severe neurodegeneration and premature death in types 2 and 3 disease. Although the basic biochemical defect is well characterized, there remains a poor understanding of the underlying pathophysiology of disease. In vitro studies suggest that macrophage glucocerebroside storage leads to tissue dysfunction through complex mechanisms involving altered intracellular calcium homeostasis and apoptosis. In order to study the pathogenic roles of these complex interactions, a viable animal model for Gaucher disease is needed. The complexity of this single gene disorder has been emphasized by the varied results of previous murine Gaucher models, ranging from perinatal lethality to phenotypically and biochemically asymptomatic animals. Recognizing the need to modulate the biochemical phenotype in mice to produce a relevant model, we have created a murine strain with key exons of the glucocerebrosidase gene flanked by loxP sites. We show that expression of Cre-recombinase in cells of hematopoietic and endothelial origin results in deficiency of glucocerebrosidase in the liver, spleen, bone marrow, and peripheral white cells. Glucocerebroside storage in this model leads to progressive splenomegaly with Gaucher cell infiltration and modest storage in the liver by 26 weeks of age. These results indicate the utility of this loxP GBA targeted murine strain for understanding the complex pathophysiology of Gaucher disease.