Hydrophilic-interaction liquid chromatography–tandem mass spectrometric determination of erythrocyte 5-phosphoribosyl 1-pyrophosphate in patients with hypoxanthine–guanine phosphoribosyltransferase deficiency

• We have developed a LC–MS/MS method for determining erythrocyte PRPP concentration.
• This method is selective and sensitive enough to measure erythrocyte PRPP concentration.
• Erythrocyte PRPP level from patients with HPRT deficiency was correlated with the disease severity.

Mutations in the gene encoding hypoxanthine–guanine phosphoribosyltransferase (HPRT) cause Lesch–Nyhan disease (LND) and its variants (LNV). Due to the technical problems for measuring the HPRT activity in vitro, discordances between the residual HPRT activity and the clinical severity were found. 5-Phosphoribosyl 1-pyrophosphate (PRPP) is a substrate for HPRT. Since increased PRPP concentrations were observed in erythrocytes from patients with LND and LNV, we have turned our attention to erythrocyte PRPP as a biomarker for the phenotype classification. In the present work, a method for determination of PRPP concentration in erythrocyte was developed using liquid chromatography–tandem mass spectrometry (LC–MS/MS) with multiple reaction monitoring (MRM). Packed erythrocyte samples were deproteinized by heating and the supernatants were injected into the LC–MS/MS system. All measurement results showed good precision with RSD <6%. PRPP concentrations of nine normal male subjects, four male patents with LND and six male patients with LNV were compared. The PRPP concentrations in erythrocyte from patients with LND were markedly increased compared with those from normal subjects, and those from patients with LNV were also increased but the degree was smaller than those with LND. The increase pattern of PRPP concentration in erythrocyte from patients with HPRT deficiency was consistent with the respective phenotypes and was correlated with the disease severity. PRPP concentration was suggested to give us supportive information for the diagnosis and the phenotype classification of LND and LNV.