A BCAA-restricted diet fortified with prescription medical foods can maintain average plasma BCAA concentrations within standard reference intervals and preserves the ratios among them. Treatment of manifestations: Treatment consists of dietary leucine restriction, BCAA-free medical foods, judicious supplementation with isoleucine and valine, and frequent clinical and biochemical monitoring. The diagnosis of MSUD is confirmed by identification of biallelic pathogenic variants in BCKDHA, BCKDHB, or DBT. Follow-up plasma amino acid analysis typically demonstrates elevated concentrations of BCAAs and alloisoleucine. Suggestive biochemical findings on NBS include whole-blood concentration ratios of (leucine + isoleucine) to alanine and phenylalanine that are above the cutoff values for the particular screening lab. In the era of newborn screening (NBS), the prompt initiation of treatment of asymptomatic infants detected by NBS means that most individuals who would have developed neonatal manifestations of MSUD remain asymptomatic with continued treatment compliance. Individuals with intermediate MSUD have partial branched-chain alpha-ketoacid dehydrogenase deficiency that manifests only intermittently or responds to dietary thiamine therapy these individuals can experience severe metabolic intoxication and encephalopathy in the face of sufficient catabolic stress. Severe intoxication culminates in critical cerebral edema, coma, and central respiratory failure. Worsening encephalopathy manifests as lethargy, apnea, opisthotonos, and reflexive "fencing" or "bicycling" movements as the sweet maple syrup odor becomes apparent in urine Early and nonspecific signs of metabolic intoxication (i.e., irritability, hypersomnolence, anorexia) are accompanied by the presence of branched-chain alpha-ketoacids, acetoacetate, and beta-hydroxybutyrate in urine įour to six days. Elevated concentrations of branched-chain amino acids (BCAAs leucine, isoleucine, and valine) and alloisoleucine, as well as a generalized disturbance of amino acid concentration ratios, are present in blood and the maple syrup odor can be detected in cerumen Neonates with classic MSUD are born asymptomatic but without treatment follow a predictable course:ġ2–24 hours. Maple syrup urine disease (MSUD) is categorized as classic (severe), intermediate, or intermittent.
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