Validation of keratan sulfate level in mucopolysaccharidosis type IVA by liquid chromatography–tandem mass spectrometry

Abstract

Mucopolysaccharidosis type IVA (MPS IVA, Morquio A disease), a progressive lysosomal storage disease, causes skeletal chondrodysplasia through excessive storage of keratan sulfate (KS). KS is synthesized mainly in cartilage and released to the circulation. The excess storage of KS disrupts cartilage, consequently releasing more KS into circulation, which is a critical biomarker for MPS IVA. Thus, assessment of KS level provides a potential screening strategy and determines clinical course and efficacy of therapies. We have recently developed a tandem mass spectrometry liquid chromatography [LC/MS/MS] method to assay KS levels in blood. Forty-nine blood specimens from patients with MPS IVA [severe (n = 33), attenuated (n = 11) and undefined (n = 5)] were analyzed for comparison of blood KS concentration with that of healthy subjects and for correlation with clinical severity. Plasma samples were digested by keratanase II to obtain disaccharides of KS. Digested samples were assayed by LC/MS/MS. We found that blood KS levels (0.4-26 µg/ml) in MPS IVA patients were significantly higher than those in age-matched controls (0.67-4.6 µg/ml; P < 0.0001). It was found that blood KS level varied with age and clinical severity in the patients. Blood KS levels in MPS IVA peaked between 2 years and 5 years of age (mean 11.4 µg/ml). Blood KS levels in severe MPS IVA (mean 7.3 µg/ml) were higher than in the attenuated form (mean 2.1 µg/ml) (P = 0.012). We also found elevated blood KS levels in other types of MPS. These findings indicate that the new KS assay for blood is suitable for early diagnosis and longitudinal assessment of disease severity in MPS IVA.

Di-sulfated Keratan Sulfate as a Novel Biomarker for Mucopolysaccharidosis II, IVA, and IVB

“…4GlcNAc(6S). Our previous results showed that the proportion of di-sulfated KS in total KS in the patients with MPS IVA is higher than that in the control subjects (Tomatsu et al 2010c); but the low sensitivity and specificity of the assay to detect di-sulfated KS limited further studies. Improvement of the assay method to separate di-sulfated KS and mono-sulfated KS was needed to distinguish MPS IVA, control subjects, and other types of MPS precisely.…”

“…Similar methods have been validated in another laboratory (Martell et al 2011). KS levels in blood and urine in patients with MPS IVA are associated with age and clinical severity (Tomatsu et al 2010c) and are decreased with enzyme replacement therapy (ERT) on mouse model and bone marrow transplantation (BMT) in a patient with MPS IVA Chinen et al 2014). Thus, KS levels in the blood and/or urine should be a suitable biomarker for early diagnosis, screening, clinical severity, and therapeutic efficacy in MPS IVA (Tomatsu et al , 2010c(Tomatsu et al , 2013a.…”

“…KS levels in blood and urine in patients with MPS IVA are associated with age and clinical severity (Tomatsu et al 2010c) and are decreased with enzyme replacement therapy (ERT) on mouse model and bone marrow transplantation (BMT) in a patient with MPS IVA Chinen et al 2014). Thus, KS levels in the blood and/or urine should be a suitable biomarker for early diagnosis, screening, clinical severity, and therapeutic efficacy in MPS IVA (Tomatsu et al , 2010c(Tomatsu et al , 2013a. However, there is significant overlap of KS levels between age-matched controls and patients with MPS IVA, especially in patients older than 10 years of age, suggesting that better biomarkers or methodology for MPS IVA are needed (Tomatsu et al 2010c).…”

“…Thus, KS levels in the blood and/or urine should be a suitable biomarker for early diagnosis, screening, clinical severity, and therapeutic efficacy in MPS IVA (Tomatsu et al , 2010c(Tomatsu et al , 2013a. However, there is significant overlap of KS levels between age-matched controls and patients with MPS IVA, especially in patients older than 10 years of age, suggesting that better biomarkers or methodology for MPS IVA are needed (Tomatsu et al 2010c). Blood KS level was also elevated in patients with MPS II and MPS IVB, resulting in difficulty to separate MPS IVA from MPS II and MPS IVB or other types of MPS by total KS (Tomatsu et al 2005(Tomatsu et al , 2010c.…”

“…However, there is significant overlap of KS levels between age-matched controls and patients with MPS IVA, especially in patients older than 10 years of age, suggesting that better biomarkers or methodology for MPS IVA are needed (Tomatsu et al 2010c). Blood KS level was also elevated in patients with MPS II and MPS IVB, resulting in difficulty to separate MPS IVA from MPS II and MPS IVB or other types of MPS by total KS (Tomatsu et al 2005(Tomatsu et al , 2010c. Patients with MPS IVA and IVB have a deficiency of the enzyme that directly involves KS metabolism, N-acetylgalactosamine-6-sulfate sulfatase (GALNS) and b-galactosidase, respectively.…”