An accurate stable isotope dilution gas chromatographic-mass spectrometric approach to the diagnosis of guanidinoacetate methyltransferase deficiency

A gas chromatography-mass spectrometry (GC-MS) method is described for the quantification of guanidinoacetate in different body fluids, using a two step derivatisation procedure which involves a reaction with hexafluoroacetylacetone to form a bis(trifluoromethyl)pyrimidine ring structure followed by a reaction with pentafluorobenzyl bromide. ¹³C₂-labelled guanidinoacetate is used as an internal standard. Bis(trifluoromethyl)pyrimidine pentafluorobenzyl derivatives were separated on a polar capillary GC-column and were quantified using negative chemical ionisation mass fragmentography. The detection limit of the method is 1 pmol guanidinoacetate in a 100 μl sample. Control values were obtained for urine (53.9±25.9 mmol mol^-1 creatinine), plasma (1.08±0.31 μmol l^-1), cerebrospinal fluid (CSF) (0.114±0.068 μmol l^-1) and amniotic fluid (3.44±0.64 μmol l^-1). The applicability of the method is illustrated by the determination of guanidinoacetate in urine, plasma and CSF of a patient affected with guanidinoacetate methyltransferase deficiency. In all body fluids of this patient, guanidinoacetate was highly elevated. Copyright (C) 1998 Elsevier Science B.V.