Case report: Lysine improvement in siblings with glutaric acidemia type 1 following reduced medical food intake: Implications for amino acid absorption and reabsorption

Glutaric acidemia type 1 (GA1) is a rare metabolic disorder requiring dietary management with lysine (Lys)-free, tryptophan (Trp)-reduced, and arginine (Arg)-fortified medical formulas. This case report describes three siblings with GA1 who exhibited persistently low plasma lysine levels despite meeting age-appropriate dietary protein intake from intact protein sources. Upon reducing medical formula intake while maintaining intact protein consumption, lysine levels normalized, suggesting that excess dietary arginine may inhibit lysine intestinal uptake or reabsorption in the kidneys. These findings highlight the need for further research on amino acid interactions in GA1 dietary management and emphasize careful formula prescription to prevent unintended lysine deficiency.