Lysosomal Storage Disorders Screen [A Test in Focus]
- Screening patients suspected of having a lysosomal storage disorder.
An Interview with Gessi Bentz Pino, CGC [Full Interview]
Gessi Bentz Pino, CGS, a Genetic Counselor in the Department of Laboratory Medicine and Pathology at Mayo Clinic, provides an overview of the lysosomal storage disorders screen, when it is appropriate to order this test, what actions the results allow you to take, and how this test improves upon previous approaches.
Advantages of Running MALDI-TOF vs. TLC
Thin layer chromatography (TLC) manually separates the oligosaccharides excreted in a urine specimen. The banding pattern is compared to negative and positive controls. The identification of the positive banding from thin layer chromatography is a subjective process dependent on the quality of the lab technique and the experience and expertise of the reviewer. While TLC methods are still widely used, the method lacks the specificity, sensitivity, and precision that can be found in newer mass spectrometry methods. The TLC method is also much more likely to have dietary artifact, especially in children younger than one year old, and lactant mothers.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry can also be used to detect oligosaccharides excreted in urine. Rather than subjective comparisons, the MALDI-TOF method precisely identifies oligosaccharides based on the known mass to charge ratio. This allows for differentiation of closely related disorders such as sialidosis from galactosialidosis. The limit of detection of the MALDI TOF is also much lower than TLC meaning even analytes in very low concentrations can be detected. MALDI-TOF also allows for the detection of additional disorders not identifiable by TLC such as beta-mannosidoses, congenital disorders of glycosylation type IIb and type NGLY1, and mucolipidoses types II and III.
Comparison of TLC (right) to MALDI-TOF (bottom) for the detection of alpha-mannosidosis. In the highlighted column of the TLC plate, a positive sample for alpha-mannosidosis is detected by the identification of six bands corresponding to the series of mannose-containing oligosaccharides. The same 6 oligosaccharides (plus 2 additional) are shown and labeled by the m/z ratio in the chromatogram.
Comparison of positive sialidosis sample by TLC (right) to MALDI-TOF (bottom). In the highlighted column of the TLC plate, a positive sample for siaidosis is detected by the identification of five bands corresponding to the series of oligosaccharides. The same 5 oligosaccharides (plus 1 additional) are shown and labeled by the m/z ratio in the chromatogram.
Oligosacchariduria Profiles by MALDI-TOF Mass Spectrometry
Oligosaccharides associated with each condition are shown with the corresponding mass-to-charge ratio (m/z). The permethylated m/z of each oligosaccharide was confirmed. Feeding formula peaks deduced based on ingredients and breast milk profiles are included to show artifacts that can be attributed to diet.
For clinical, specimen, and performance information, please visit the Lysosomal Storage Disorders Screen, Urine page in our test catalog.