Abstract
We have suggested that carnitine modulates the acyl CoA:CoA ratio in the organic acidurias. Temporary withdrawal (at parental request) of vitamin B12 in a 7 year old developmentally normal boy with MMA provided an opportunity to test this. Free carnitine (fc) and acylcarnitines (ac) were measured by a radioenzymatic method and organic acids by gas chromatography. Initially plasma carnitines were (mean ± 1SD, n=4): fc 17.6 (2.5), ac 10.7 (3.8) μmol/l; normals 5-12 years), (mean ± 1SD n=20): fc 37.7 (7.7) (sig. diff p < .001), ac 7.1 (5.3) μmol/1). 24 hour carnitine excretion was : fc 4.3 μmol, ac 141.1μmol (mainly propionyl), ac:fc 32.6 (normal < 10). Plasma methylmalonate (ma.) was 142 μmol/l and 24 hour excretion was 22.3 mmol (normally undetectable). Reduction in B12 caused a fall in plasma fc to 2.5 and a rise in ac to 19.4 μmol/l. Plasma ma. rose to 686 μmol/l and urinary excretion to 126.2 mmol/24 hrs with associated clinical deterioration. B12 was recommended. Plasma fc rose to 16.3 μmol/l. Plasma ma. fell to 165 μmol/l and urinary excretion to 6.9 μmol/24 hours with clinical improvement. Redistribution of plasma carnitine between free and acylcarnitines reflected intramitochondrial depletion of Coenzyme A which followed from accumulation of abnormal metabolites as their CoA esters on stopping B12. These changes reversed when cofactor was recommended. This provides further evidence for a modulating effect of carnitine on acyl CoA:CoA.
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de Sousa, C., Chalmers, R., Tracey, B. et al. CHANGES IN CARNITINE AND METHYLMALONATE FOLLOWING WITHDRAWAL OF VITAMIN B12 IN B12 RESPONSIVE METHYLMALONIC ACIDURIA (MMA). Pediatr Res 19, 1074 (1985). https://doi.org/10.1203/00006450-198510000-00040
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DOI: https://doi.org/10.1203/00006450-198510000-00040
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