Abstract
The dopamine concentration in the caudate nucleus of two PKU patients with high blood phenylalanine was drastically reduced / < 1.9 ng/100 ug protein/ compared with five control persons /ca. 12 ng/100 ug protein/. The biopsy samples were obtained during therapeutic stereotactic surgery and analyzed by mass fragmentography of the N,0-trifluoroacetyl derivatives. Earlier experiments had shown that these patients excrete subnormal amounts of dopamine and catecholamine metabolites in urine. The analysis of brain biopsies confirms our postulation that the conversion of tyrosine to L-dopa by tyrosine 3-hydroxylase is inhibited by high phenylalanine concentrations also in vivo. The deficiency of catecholamines in the brain may be an important factor in the pathogenesis of the neurological symptoms and of the mental retardation observed in untreated PKU patients.
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