MEDizzy - A patient has a “pill-rolling” tremor, “cogwheel” rigidity,

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Amino Acid Metabolism and the Urea Cycle

A patient has a “pill-rolling” tremor, “cogwheel” rigidity, bradykinesis, speech difficulties, and a shuffling gait. The chemical that is lacking in this syndrome is a derivative of which of the following amino acids?

ExplanationThis patient has Parkinson disease, which is a problem with dopamine synthesis in the substantia nigra. Dopamine is derived from tyrosine. Treatment with DOPA in the initial stages of the disease provides relief from the symptoms. DOPA cannot be synthesized from alanine, serine, or tryptophan.