6 Like PKU, treating MSUD relies on minimizing pathologic amino acid accumulation and introducing other competitive amino acids to maintain adequate neuronal homeostasis. They further propose that acute elevations in alpha-ketoacids and leucine cause metabolic encephalopathy and cerebral edema. Accumulation of BCAAs overwhelms the nonselective uptake transporters, which causes a reduced transport of other amino acids for neuronal anabolism. also proposed a similar mechanism for MSUD neuronal interference. In-depth studies of the more common metabolic derangement, PKU, seemingly demonstrate cerebral amino acid transport system interference and inhibition of myelin formation as the pathologic mechanism. Proposed cerebral amino acid deprivation mechanisms pertaining to MSUD are rarely studied in the literature and reference texts. Accumulation of acids in blood then causes metabolic acidosis, electrolyte disturbances, and neurotransmitter anabolism dysfunction. Without appropriate metabolism by the branched-chain alpha-ketoacid dehydrogenase enzyme (BCKDH), they cannot undergo further catabolism.
1 In the first step of BCAA degradation, globally present mitochondrial transaminases convert the BCAAs valine, isoleucine, and leucine to alpha-ketoacid form. 1 It should be noted that leucine is strictly ketogenic and not utilized to form glucose. With BCAAs composing 25% of consumable proteins, they account for an important source of energy for gluconeogenesis metabolism in low-glucose states. In MSUD, the inability to break down branched-chain amino acids (BCAAs) causes rapid accumulation of these essential amino acids in the blood. 5 The most common amino acid metabolic syndromes likely to be encountered in a treatment setting include cystinuria and phenylketonuria (PKU). Although these metabolic defects are exceedingly rare, with each present in less than 1 per 100,000 live births, higher MSUD incidences have been reported in Mennonite populations. Frequently, the enzyme deficiencies become evident in the first month of life after investigating a newborn’s failure to thrive. 2–4 Such disorders are often revealed by traditional newborn screening techniques. 1 The incidence of the disease is estimated at 1 in 185,000 live births in various texts, which is consistent with other similarly rare amino acid metabolism disorders such as homocystinuria, alkaptonuria, and methyl malonyl CoA mutase deficiency.
The possible underlying mechanism of this neuropsychological profile is discussed in relation to other neurodevelopmental models.Maple syrup urine disease (MSUD), an amino acid catabolism disorder, gets its name from the sweet smell of urine associated with the disease. This case demonstrates neurocognitive deficiencies within the context of normal magnetic resonance imaging. The patient also showed reduced adaptive functioning and mild anxiety. Neuroimaging revealed no structural abnormalities, while the results from the neuropsychological evaluation showed impairment in visual-spatial processing, attention, executive functioning, and psychomotor abilities, with relative strengths in verbal skills. In the present paper, we report an adult case of MSUD with associated neurocognitive deficits and functional limitations following liver transplantation. Even with successful management of MSUD there is evidence from pediatric cases that shows a distinct pattern of neurocognitive deficits associated with this condition, including impaired nonverbal skills and psychomotor functioning with relatively intact verbal abilities. Acute and long-term management of MSUD involves a restricted diet and regular monitoring of amino acid levels however, more recently liver transplants have been shown to be successful in treating this condition. Maple syrup urine disease (MSUD) is a rare hereditary metabolic condition where the body is unable to breakdown amino acids causing toxic buildup.
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