Étude des acylcarnitines plasmatiques par spectrométrie de masse en tandem. Application au diagnostic des maladies héréditaires du métabolisme

Abstract

L-carnitine is known to transport long chain fatty acids through the mitochondrial membrane but also to export accumulated acyl-CoA's as acylcarnitine esters. Acylcarnitine identification in body fluids allows the diagnosis of mitochondrial inborn errors especially fatty oxidation defects. Tandem mass spectrometry represents a new method for isolation and identification of acylcarnitines in plasma or in blood spotted onto filter paper (Guthrie cards). In order to validate our method, we studied 30 plasmas from children affected with 15 different inborn errors of metabolism and five amniotic fluids from fetuses affected with several organic acidurias. Fourty-six samples from children at risk for mitochondrial fatty oxidation disorders have been analyzed. We developed a method of tandem mass spectrometry with liquid secondary ion mass spectrometry using deuterated acylcarnitines as internal standards. This method is very sensitive (detection limit = 2 microM). In all affected patients specific acylcarnitine signals corresponding to the metabolic block were constantly found. This confirms the diagnosis and validates the method. Among the 46 at risk children, four defects of long chain fatty acid oxidation were identified. This new method is of great interest especially for the long chain fatty acid oxidation defects. These defects are very difficult to diagnose with classical methods as urinary organic acid profiling. A small amount of plasma (100 microL) or blood spotted onto paper is required. The acylcarnitine profile allows a rapid diagnosis if a dedicated apparatus is available.