Development and evaluation of quality control dried blood spot materials in newborn screening for lysosomal storage disorders.

BACKGROUND

Lysosomal storage disorders (LSDs) comprise more than 40 genetic diseases that result in the accumulation of products that would normally be degraded by lysosomal enzymes. A tandem mass spectrometry (MS/MS)-based method is available for newborn screening for 5 LSDs, and many laboratories are initiating pilot studies to evaluate the incorporation of this method into their screening panels. We developed and evaluated dried blood spot (DBS) QC materials for LSDs and used the MS/MS method to investigate their suitability for LSD QC monitoring.

METHODS

We incubated 3.2-mm punches from DBS controls for 20-24 h with assay cocktails containing substrate and internal standard. Using MS/MS, we quantified the resulting product and internal standard. Samples were run in triplicate for 3 consecutive days, and results were reported as product-to-internal standard ratios and enzyme activity units (micromol/L/h).

RESULTS

Enzyme activity interday imprecision (CV) for the high, medium, and low series were 3.4%-14.3% for galactocerebroside alpha-galactosidase, 6.8%-24.6% for acid alpha-galactosidase A, 7.36%-22.1% for acid sphingomyelinase, 6.2%-26.2% for acid alpha-glucocerebrosidase, and 7.0%-24.8% for lysosomal acid alpha-glucosidase (n = 9). In addition, DBS stored at -20 degrees and 4 degrees C showed minimal enzyme activity loss over a 187-d period. DBS stored at 37 degrees and 45 degrees C had lower activity values over the 187-day evaluation time.

CONCLUSIONS

Suitable QC materials for newborn screening of LSDs were developed for laboratories performing DBS LSD screening. Good material linearity was observed, with goodness-of-fit values of 0.953 and higher. The QC materials may be used by screening laboratories that perform LSD analysis by MS and/or more conventional fluorescence-based screening methods.