This record contains raw data related to the article "Plasma phospholipid dysregulation in patients with cystathionine-β synthase deficiency" ABSTRACT Background & Aims: Patients with cystathionine β-synthase deficiency (CBSD) exhibit high circulating levels of homocysteine and enhanced lipid peroxidation. Because enhanced homocysteine plays key roles in methylation reactions that govern lipid metabolism, we have characterized the plasma lipidome in CBSD patients. Methods and results: Using an ultra-high-performance liquid chromatography-electrospray ionization-quadrupole-time of flight- mass spectrometry method, plasma lipids were determined with an untargeted lipidomics approach in 11 CBSD patients and 11 matched healthy subjects (CTRL). Compared to CTRL, CBSD patients had a higher medium and long-chain polyunsaturated fatty acids (PUFA) content in phosphatidylethanolamine (PE) and lysophosphatidylethanolamine (LPE) species (p<0.02), and depletion of phosphatidylcholine (PC; p=0.02) and of lysophosphatidylcholine (LPC; p=0.003) species containing docosahexaenoic acid (DHA), suggesting impaired phosphatidylethanolamine-N-methyltransferase (PEMT) activity. PEMT needs methyl groups to convert PE into PC, S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). Whole blood SAM and SAH concentrations by liquid chromatography tandem mass spectrometry were 1.4-fold (p=0.015) and 5.3-fold (p=0.003) higher in CBSD patients than in CTRL. A positive correlation between SAM/SAH and PC/PE ratios (r=0.520; p=0.019) was found. Conclusions: A novel biochemical abnormality in CBSD patients consisting in depletion of PC and LPC species containing DHA and accumulation of PUFA in PE and LPE species is revealed by this lipidomic approach. Changes in plasma SAM and SAH concentrations are associated with such phospholipid dysregulation. Given the key role of DHA in thrombosis prevention, depletion of PC species containing DHA in CBSD patients provides a new direction to understand the poor cardiovascular outcome of patients with homocystinuria and hyperhomocysteinemia. The data are those produced at Centro Cardiologico Monzino