Effectiveness of Riboflavin in Inherited Metabolic Diseases: A Systematic Review.

Riboflavin (RF, vitamin B2) is an essential vitamin of which the co-factors are critical to numerous cellular processes. RF is used as a treatment for inherited metabolic diseases (IMDs), although its effectiveness in many disorders has not been established. We aim to summarize all available data on the efficacy and safety of RF in the management of IMDs. A systematic literature search was conducted for articles reporting the effectiveness of RF in IMDs. RF therapy was considered "effective" in an IMD if more than 75% of patients showed a positive response, "uncertain" in case of a positive response in fewer than 75% of patients, and "not effective" if patients deteriorated or died following RF therapy. RF therapy was reported in 381 articles addressing 33 separate IMDs. A positive effect was established in MADD type 3 (n=536, 93.1% responsive), RTD 2,3 (n = 94, 90.4% responsive), ACAD 9 (n = 29, 75.9% responsive), and FAD transporter deficiency (n = 5, 100% responsive). The effect was uncertain in complex I and II deficiency, ethylmalonic encephalopathy, FAD synthase deficiency, glutaric aciduria type 1, L2 hydroxyglutaric aciduria, and MADD type 2. RF was not effective in MADD type 1. Adverse effects were infrequent and mild. RF therapy in MADD type 3, RTD 2 and 3, ACAD9, and FAD transporter deficiency is safe and effective. Access to RF for these patients is crucial. For a substantial group of IMDs, the effect of RF remains uncertain. In these conditions, a trial of RF therapy with clearly defined outcome criteria might be considered.