Based on the clinical presentation and the sweet-smelling urine, the newborn most likely has maple syrup urine disease. Therefore, branched-chained amino acids should be restricted such as valine.
Maple syrup disease is an autosomal recessive disease due to a deficiency in branched-chain ketoacid dehydrogenase. Individuals with the disease are unable to breakdown branched-chain amino acid such as valine, leucine, and isoleucine. Onset typically begins in the first week of life, and symptoms are progressive. Symptoms include the classic sweet maple syrup smell of urine, lethargy, weight loss, hypotonia, mental retardation, poor feeding, and opisthotonus (abnormal, hyperextended posturing). If branched-chain amino acids are not excluded from the diet, coma and death ensues within a matter of days.
Frazier et al. discuss the recommendations for intake of the branched-chain amino acids. Since valine, leucine, and isoleucine are essential amino acids, patients with maple syrup disease do need these amino acids for proper growth and development but only the minimum amount should be consumed. The need is highest during the ages of 0-6 months, as growth is rapid during this time period. Recommended intake of leucine is 40-100 mg/kg, isoleucine is 30-90 mg/kg, and valine is 40-95 mg/kg. As the patients age, their requirements decrease. For example adults (19+) only need 15-50 mg/kg, 10-30 mg/kg, and 15-30 mg/kg, respectively.
Strauss et al. discuss the screening and diagnosis of maple syrup disease. Diagnosis is based on the clinical presentation as discussed above, elevated levels of valine, leucine, isoleucine, and allo-leucine in the blood and in urine. As for newborn screening, tandem mass spectrometry measures the ratio of leucine plus isoleucine to other amino acids such as alanine and phenylalanine in the blood.
Illustration A shows the branched-chain amino acids (valine, leucine, and isoleucine).
Answer 1,3-5: These amino acids do not pose a problem to patients with maple syrup disease, as they contain the necessary enzymes to metabolize these amino acids.
Frazier DM, Allgeier C, Homer C, Marriage BJ, Ogata B, Rohr F, Splett PL, Stembridge A, Singh RH. Nutrition management guideline for maple syrup urine disease: an evidence- and consensus-based approach. Mol Genet Metab. 2014 Jul;112(3):210-7. doi: 10.1016/j.ymgme.2014.05.006.
PMID:24881969 (Link to Abstract)
Strauss KA, Puffenberger EG, Morton DH. Maple Syrup Urine Disease. 2006 Jan 30 [Updated 2013 May 9]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2015. Available from: http://www.ncbi.nlm.nih.gov/books/NBK1319/