Improved detection of long-chain fatty acid oxidation defects in intact cells using [9,10-3H]oleic acid.

Abstract

[9,10- 3 H]Myristate and [9,10- 3 H]palmitate are currently used widely in 3 H 2 O release assays for detecting medium- and long-chain fatty acid oxidation defects, both in intact fibroblasts (Manning et al 1990; Olpin et al 1992) and in lymphocytes (Brivet et al 1995). Over the past nine years we have used both substrates to screen routinely for fatty acid oxidation defects in over 900 patients and have identified 82 individuals with specific fatty acid oxidation disorders. Nearly all of these assays have been performed on fibroblasts. Medium-chain acyl-CoA dehydrogenase deficiency (McKusick 201450) is characterized by a much decreased oxidation of myristate, giving a high palmitate/myristate (P/M) ratio. The long-chain defects, very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency (McKusick 143450), generally give a low P/M ratio, though discrimination is relatively poor. This is particularly true for 'mild' VLCAD, where both absolute activities with [9,10- 3 H]myristate and [9,10- 3 H]palmitate and the P/M ratio may show overlap with the control range. Over the last few years we have increasingly encountered patients who present both clinically and biochemically as likely to have a fatty acid oxidation disorder and with mild to moderate reductions (into the VLCAD and LCHAD range) in fibroblast oxidation of [9,10- 3 H]myristate and [9,10- 3 H]palmitate but who do not meet the criteria for any of the recognized fatty acid oxidation defects. We now describe the use of [9,10- 3 H]oleic acid, a commercially available substrate, for improved discrimination in the detection of long-chain fatty acid oxidation defects.