We speculate that citrulline supplementation, as provided during AMD in urea cycle disorders as N-acetylglutamate synthase deficiency, carbamoyl phosphate synthase I deficiency and ornithine transcarbamylase deficiency to maximize ammonia excretion through the urea cycle [35], might also contribute to ammonia detoxification in severely decompensated PA and MMA patients, but this hypothesis requires further study. This evidence concerns the gene NAGS and urea cycle disorder.