Abstract
Adult Refsum disease (ARD) is associated with defective alpha-oxidation of phytanic acid (PA). omega-Oxidation of PA to 3-methyl-adipic acid (3-MAA) occurs although its clinical significance is unclear. In a 40 day study of a new ARD patient, where the plasma half-life of PA was 22.4 days, omega-oxidation accounted for 30% initially and later all PA excretion. Plasma and adipose tissue PA and 3-MAA excretion were measured in a cross-sectional study of 11 patients. The capacity of the omega-oxidation pathway was 6.9 (2.8-19.4) mg [20.4 (8.3-57.4) micromol] PA/day. 3-MAA excretion correlated with plasma PA levels (r = 0.61; P = 0.03) but not adipose tissue PA content. omega-Oxidation during a 56 h fast was studied in five patients. 3-MAA excretion increased by 208 +/- 58% in parallel with the 158 (125-603)% rise in plasma PA. Plasma PA doubled every 29 h, while 3-MAA excretion followed second-order kinetics. Acute sequelae of ARD were noted in three patients (60%) after fasting. The omega-oxidation pathway can metabolise PA ingested by patients with ARD, but this activity is dependent on plasma PA concentration. omega-Oxidation forms a functional reserve capacity that enables patients with ARD undergoing acute stress to cope with limited increases in plasma PA levels.
Highlights
Adult Refsum disease (ARD) is associated with defective ␣-oxidation of phytanic acid (PA). -Oxidation of PA to 3-methyl-adipic acid (3-MAA) occurs its clinical significance is unclear
Analysis of the kinetics of 3-MAA levels in this patient showed they were linear when plotted against 1/[C] Ϫ 1/[Co], and demonstrated second-order kinetics
Despite supervision, showed an increase in PA intake as measured by the food intake questionnaire, yet their PA levels fell over the period of the study, demonstrating that either acute variations in dietary intake were identified in the questionnaire or the slow kinetics of plasma PA response to dietary-induced changes
Summary
Adult Refsum disease (ARD) is associated with defective ␣-oxidation of phytanic acid (PA). -Oxidation of PA to 3-methyl-adipic acid (3-MAA) occurs its clinical significance is unclear. This study assessed the contribution made by the -oxidation pathway to the metabolism of PA by measuring 3-MAA excretion in patients with ARD. Despite supervision, showed an increase in PA intake as measured by the food intake questionnaire, yet their PA levels fell over the period of the study, demonstrating that either acute variations in dietary intake were identified in the questionnaire or the slow kinetics of plasma PA response to dietary-induced changes.
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