Clinical utility of low branched-chain amino acid modular diets in patients with isovaleric aciduria and maple syrup urine disease

@#Introduction: Modular diets (MDs) with low amount of offending amino acids have been developed using locally available food ingredients as alternatives to commercial formulas for the treatment of branched-chain organic acidurias (BCOAs). Herein, we conducted a clinical investigation of MDs in patients with BCOAs. Methods: Modular diet A (MDA), with low leucine was produced for maple syrup urine disease (MSUD), and modular diet B (MDB) products, MDB-1, -2, -3, and -4, with low leucine, valine, methionine and threonine were made for isovaleric aciduria (IVA)/methylmalonic aciduria (MMA)/propionic aciduria (PA). Children aged 4-18 years, with MSUD, IVA, PA or MMA were invited to participate in the study. The research subjects switched from metabolic formula protocol to modular diet protocol. They were followed-up at 0, 1, 2, 4, and 6 months. Clinical efficacies of MDs were determined by completion of study, compliance to MDs, clinical outcomes and complications, and parental satisfaction. Results: Six children (2 MSUD and 4 IVA) participated and completed the study. Compliance to MDA was 100% in MSUD subjects with G-tube feeding, while compliance to MDB varied among self-fed individuals with IVA. One subject with MSUD was clinically stable throughout the study, while the other experienced metabolic instability. All IVA individuals showed clinical and laboratory stability during the study. One MSUD and three IVA families preferred the metabolic formula, whereas the other IVA family reported no preference and the other MSUD subject preferred MDs. Conclusion: We provided a proof of concept in developing modular diets for BCOAs, and showed favourable outcomes when using MDs in IVA and varying clinical benefits in MSUD.

Integrated Multianalyte Second-Tier Testing for Newborn Screening for MSUD, IVA, and GAMT Deficiencies

Abstract Advances in mass spectrometry have allowed for expansion of newborn screening test panels over the last decade but with increased numbers of disorders have come increased concerns with false-positive rates. The introduction of second-tier testing has improved the specificity of screening for a number of disorders without any corresponding sacrifice in sensitivity. Such testing does, however, put pressure on scarce laboratory resources including instrument and personnel time and even the bloodspot sample itself. The British Columbia Newborn Screening Program has developed an integrated second-tier screening approach to improve test performance without the requirement to resample and reprocess the original bloodspot specimen. By utilizing the residual extract from the first-tier assay and introducing a chromatography step as the second tier, we have been able to reduce false-positive rates due to interfering isobaric compounds for 3 different disorders (maple syrup urine disease, isovaleric aciduria, and guanidinoacetate methyltransferase) in a single multianalyte assay.

Clinical and genetic features of three patients with non-classical isovaleric aciduria / 临床儿科杂志

Objective To explore the clinical, therapeutic and genetic features of IVD gene in late-onset non-classical isovaleric aciduria. Methods One boy and two girls presented with intractable vomiting were admitted. Urine organic acids and blood acylcarnitines proifles were analyzed. Isovaleric aciduria was diagnosed and conifrmed by IVD gene analysis. The patients were treated with leucine-restricted diet and the supplements of L-carnitine and glycine. Results Three patients had recurrent vomiting, drowsiness, odor of sweaty feet and metabolic acidosis from the age of 1 to 2 years. All of them had normal intelligence and leukopenia. One had oligocythemia. The blood isovalerylcarnitines (4.6 to 8.2μmol/L) and urine isovalerylglycines (36.1 to 1783.56 mmol/mmol creatinine) were elevated. Six mutations were found in their IVD gene. Four mutations (c.157C>T, c.214G>A, c.1183C>G and c.1208A>G) were reported. Two (c.1039G>A and c.1076A>G) were novel. The patients completely recovered after treatment with protein-restricted diet and the supplements of L-carnitine and glycine. Currently, they were aged 19 months to 14 years with normal physical and psychomotor development. Conclusions The clinical features of late-onset non-classical isovaleric aciduria are complex. It is onset in infants and young children and characteristic of recurrent vomiting and metabolic acidosis, which can be diagnosed by the blood acylcarnitine spectrum, urine organic acid analysis, and conifrmed by genetic analysis. L-carnitine supplement and diet intervention has signiifcant effects.