PLASMA CIS-DEC-4-ENOIC ACID MEASURED BY ISOTOPE-DILUTION MASS-SPECTROMETRY - AN IMPROVED ASSAY TO DIAGNOSE MEDIUM-CHAIN ACYL-COA DEHYDROGENASE-DEFICIENCY

An isotope dilution mass spectrometric assay for plasma cis-dec-4-enoi c acid is described. It is quicker, more reliable and more accurate th an previous methods. It confirmed previous findings that cis-dec-4-eno ic acid is a reliable indicator for medium-chain acyl-CoA dehydrogenas e deficiency (MCAD). The plasma cis-dec-4-enoic acid levels of both as ymptomatic and symptomatic MCAD patients (3.5-71 mu mol/L) are demonst rably higher than those of normal children (0.2-1.7 mu mol/L), MCAD he terozygotes (0.1-1.5 mu mol/L), those with other fatty acid oxidation defects (0.2-2.2 mu mol/L) or those receiving high doses of valproic a cid (0.2-0.4 mu mol/L).