Quantitative Keratan Sulfate Analysis
Mucopolysaccharidoses (MPS) refer to a group of lysosomal storage diseases characterized by defects in the enzymes needed for degradation of glycosaminoglycans (GAGs). Seven types of MPS disorders have been classified based on the pathway affected. Eleven enzymes are involved in the catabolic pathways of the GAGs and deficiencies in enzymes responsible for the degradation of keratan sulfate (KS) lead to MPS IV, or Morquio Syndrome.
The most common form of MPS, MPS IV Type A, is associated with loss-of-function mutations in the GALNS gene, which normally produces the enzyme N-acetylgalactosamine 6-sulflatase. Loss of function mutations of GLB1, which normally produces the enzyme beta-galactosidase, results in the less common MPS IV type B. In general, MPS disorders are multi-systemic, with progressive involvement of the visceral organs and bones. The loss of this enzymatic activity results in an accumulation of KS in lysosomes and ultimately leads to clinical manifestations, which for MPS IV (type A and B) include severe skeletal anomalies, short stature, and atlanto-axial instability. Unique among MPS disorders, MPS IV patients generally have normal intelligence and no apparent CNS involvement. Non-degraded or partially degraded fragments of KS are excreted in the urine and can be used for the screening and diagnosis of MPS IV.
We utilize a quantitative LC-MS/MS approach to analyze urinary KS levels. In this assay, urinary KS is digested into its specific disaccharide units by enzymatic digestion before analysis by LC-MS/MS. KS is quantified as the total abundance of sulfate-conjugated N-acetyl lactose disaccharides (LacNAc-1S and LacNAc-2S) measured using C13-labeled internal standards. This assay accurately measures KS concentrations from 0.1 – 100 µg/ml. Findings can be further confirmed by either enzyme analysis or molecular analysis of the relevant genes.
- Urine: 3-5 mL (random void) in a clean container without any preservatives. Minimum of 1 mL is required. The sample should be stored frozen until analysis
- Ship overnight frozen on dry ice
- 5 days