Untargeted metabolomics and infrared ion spectroscopy identify biomarkers for pyridoxine-dependent epilepsy
Udo F.H. Engelke, Rianne E. van Outersterp, Jona Merx, Fred A.M.G. van Geenen, Arno van Rooij, Giel Berden, Marleen C.D.G. Huigen, Leo A.J. Kluijtmans, Tessa M.A. Peters, Hilal H. Al-Shekaili, Blair R. Leavitt, Erik de Vrieze, Sanne Broekman, Erwin van Wijk, Laura A. Tseng, Purva Kulkarni, Floris P.J.T. Rutjes, Jasmin Mecinović, Eduard A. Struys, Laura A. Jansen, Sidney M. Gospe Jr., Saadet Mercimek-Andrews, Keith Hyland, Michèl A.A.P. Willemsen, Levinus A. Bok, Clara D.M. van Karnebeek, Ron A. Wevers, Thomas J. Boltje, Jos Oomens, Jonathan Martens, Karlien L.M. Coene
Udo F.H. Engelke, Rianne E. van Outersterp, Jona Merx, Fred A.M.G. van Geenen, Arno van Rooij, Giel Berden, Marleen C.D.G. Huigen, Leo A.J. Kluijtmans, Tessa M.A. Peters, Hilal H. Al-Shekaili, Blair R. Leavitt, Erik de Vrieze, Sanne Broekman, Erwin van Wijk, Laura A. Tseng, Purva Kulkarni, Floris P.J.T. Rutjes, Jasmin Mecinović, Eduard A. Struys, Laura A. Jansen, Sidney M. Gospe Jr., Saadet Mercimek-Andrews, Keith Hyland, Michèl A.A.P. Willemsen, Levinus A. Bok, Clara D.M. van Karnebeek, Ron A. Wevers, Thomas J. Boltje, Jos Oomens, Jonathan Martens, Karlien L.M. Coene
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Clinical Research and Public Health Metabolism

Untargeted metabolomics and infrared ion spectroscopy identify biomarkers for pyridoxine-dependent epilepsy

Abstract

Background Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is an inborn error of lysine catabolism that presents with refractory epilepsy in newborns. Biallelic ALDH7A1 variants lead to deficiency of α-aminoadipic semialdehyde dehydrogenase/antiquitin, resulting in accumulation of piperideine-6-carboxylate (P6C), and secondary deficiency of the important cofactor pyridoxal-5′-phosphate (PLP, active vitamin B6) through its complexation with P6C. Vitamin B6 supplementation resolves epilepsy in patients, but intellectual disability may still develop. Early diagnosis and treatment, preferably based on newborn screening, could optimize long-term clinical outcome. However, no suitable PDE-ALDH7A1 newborn screening biomarkers are currently available.Methods We combined the innovative analytical methods untargeted metabolomics and infrared ion spectroscopy to discover and identify biomarkers in plasma that would allow for PDE-ALDH7A1 diagnosis in newborn screening.Results We identified 2S,6S-/2S,6R-oxopropylpiperidine-2-carboxylic acid (2-OPP) as a PDE-ALDH7A1 biomarker, and confirmed 6-oxopiperidine-2-carboxylic acid (6-oxoPIP) as a biomarker. The suitability of 2-OPP as a potential PDE-ALDH7A1 newborn screening biomarker in dried bloodspots was shown. Additionally, we found that 2-OPP accumulates in brain tissue of patients and Aldh7a1-knockout mice, and induced epilepsy-like behavior in a zebrafish model system.Conclusion This study has opened the way to newborn screening for PDE-ALDH7A1. We speculate that 2-OPP may contribute to ongoing neurotoxicity, also in treated PDE-ALDH7A1 patients. As 2-OPP formation appears to increase upon ketosis, we emphasize the importance of avoiding catabolism in PDE-ALDH7A1 patients.Funding Society for Inborn Errors of Metabolism for Netherlands and Belgium (ESN), United for Metabolic Diseases (UMD), Stofwisselkracht, Radboud University, Canadian Institutes of Health Research, Dutch Research Council (NWO), and the European Research Council (ERC).

Authors

Udo F.H. Engelke, Rianne E. van Outersterp, Jona Merx, Fred A.M.G. van Geenen, Arno van Rooij, Giel Berden, Marleen C.D.G. Huigen, Leo A.J. Kluijtmans, Tessa M.A. Peters, Hilal H. Al-Shekaili, Blair R. Leavitt, Erik de Vrieze, Sanne Broekman, Erwin van Wijk, Laura A. Tseng, Purva Kulkarni, Floris P.J.T. Rutjes, Jasmin Mecinović, Eduard A. Struys, Laura A. Jansen, Sidney M. Gospe Jr., Saadet Mercimek-Andrews, Keith Hyland, Michèl A.A.P. Willemsen, Levinus A. Bok, Clara D.M. van Karnebeek, Ron A. Wevers, Thomas J. Boltje, Jos Oomens, Jonathan Martens, Karlien L.M. Coene

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Figure 3

2-OPP and 6-oxoPIP concentrations in PDE-ALDH7A1 patient body fluids.

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2-OPP and 6-oxoPIP concentrations in PDE-ALDH7A1 patient body fluids. Ab...
Absolute concentration of 6-oxoPIP and the sum of 2S,6S-2-OPP and 2S,6R-2-OPP in (A and B) plasma (n = 11), (C and D) urine (n = 8), and (E and F) CSF (n = 9) of PDE-ALDH7A1 patients (PDE) compared with non-IEM controls (n = 16 for plasma, n = 16 for urine, n = 13 for CSF), as measured by quantitative LC-MS/MS. Different treatment regimens in patients are coded as follows: open circles, untreated; filled squares, vitamin B6 supplementation; filled circles, vitamin B6 and arginine supplementation; filled triangles, vitamin B6 supplementation and lysine restriction; filled diamonds, vitamin B6 and arginine supplementation and lysine restriction; cross, therapy unknown. Data are shown as the mean and interquartile range. All patient 2-OPP and 6-oxoPIP concentration ranges shown were significantly increased compared with controls (Mann-Whitney U test; CSF 6-oxoPIP patients versus controls P ≤ 0.0008, all other conditions P ≤ 0.0001).