Exploring metabolic alterations in PYCR2 deficiency: Unveiling pathways and clinical presentations of hypomyelinating leukodystrophy 10

Proline-5-carboxylate reductase 2, encoded by PYCR2 gene, is an enzyme that catalyzes the last step of proline synthesis from pyrroline-5-carboxylate synthetase to proline. PYCR2 gene defect causes hypomyelinating leukodystrophy 10. Up until now, to our knowledge around 38 patients with PYCR2 defect have been reported. Herein, we describe clinical, neuroradiological, biochemical findings, and metabolomic profiling of three new genetically related cases of PYCR2 defects from a large family. Cerebrospinal fluid (CSF) amino acid levels were measured and untargeted metabolomic profiling of plasma and CSF were conducted and evaluated together with the clinical findings in the patients. While plasma and CSF proline levels were found to be totally normal, untargeted metabolomic profiling revealed mild increases of glutamate, alpha-ketoglutarate, and l-glutamate semialdehyde and marked increases of inosine and xanthine. Our findings and all the previous reports suggest that proline auxotrophy is not the central disease mechanism. Untargeted metabolomics point to mild changes in proline pathway and also in purine/pyrimidine pathway.