Direct tandem mass spectrometric profiling of sulfatides in dry urinary samples for screening of metachromatic leukodystrophy
Abstract
Background: Prediagnostic steps in suspected metachromatic leukodystrophy (MLD) rely on clinical chemical methods other than enzyme assays. We report a new diagnostic method which evaluates changes in the spectrum of molecular types of sulfatides (3-O-sulfogalactosyl ceramides) in MLD urine.
Methods: The procedure allows isolation of urinary sulfatides by solid-phase extraction on DEAE-cellulose membranes, transportation of a dry membrane followed by elution and tandem mass spectrometry (MS/MS) analysis in the clinical laboratory. Major sulfatide isoforms are normalized to the least variable component of the spectrum, which is the indigenous C18:0 isoform.
This procedure does not require the use of specific internal standards and minimizes errors caused by sample preparation and measurement. Results: Urinary sulfatides were analyzed in a set of 21 samples from patients affected by sulfatidosis.
The combined abundance of the five most elevated isoforms, C22:0, C22:0-OH, C24:0, C24:1-OH, and C24:0-OH sulfatides, was found to give the greatest distinction between MID-affected patients and a control group. Conclusions: The method avoids transportation of liquid urine samples and generates stable membrane-bound sulfatide samples that can be stored at ambient temperature.
MS/MS sulfatide profiling targeted on the most MLD-representative isoforms is simple with robust results and is suitable for screening.