Very long chain fatty acids
5 mL blood in lithium heparin or plain tube.
Chorionic villus biopsy; skin biopsy.
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Diagnosis of adrenoleukodystrophy, adrenomyeloneuropathy and some other peroxisomal disorders (eg, Zellweger syndrome).
Elevation of the ratio of C26 fatty acids or C24 fatty acids to C22 fatty acids indicates a defect in oxidation of very long chain fatty acids, an exclusively peroxisomal function. This occurs in genetic deficiencies of a specific enzyme in the oxidation pathway (eg, adrenoleukodystrophy), or generalised peroxisomal dysfunction (eg, Zellweger syndrome).
The test is performed most conveniently on plasma, but cells (eg, cultured skin fibroblasts) can also be used and antenatal diagnosis can be performed on chorionic villus samples.
Carriers of adrenoleukodystrophy (which is X-linked) usually show increased levels but the test is not 100% sensitive.
Brown FR et al. Amer J Dis Child. 1993; 147: 617-626.