Plasma amino acids and neopterin in healthy persons with Down's syndrome

In persons with Down's syndrome (DS) immunological abnormalities as well as hypothyroidism and Alzheimer type dementia are frequently observed. In addition, the activity of the enzyme cystathionine beta-synthase (CBS) is over-expressed which results in an altered homocysteine metabolism. In the present study, 48 older healthy DS persons without signs of dementia, psychiatric or somatic comorbidity and free of medication were analyzed for plasma levels of amino acids, neopterin and monoaminergic metabolites. Data were compared with those obtained from age and sex matched healthy controls. It was found that the spectrum of amino acids showed widespread differences in that levels of nearly all essential amino acids were lower in DS patients as compared to healthy controls. In addition, a significantly lower methionine and higher taurine concentration were observed which is in accordance with a disturbed homocysteine metabolism. With respect to the monoamine metabolites, the concentration of 5-hydroxyindoleacetic acid was not altered whereas that of homovanillic acid was significantly increased. Finally, the concentration of the immune activation marker neopterin was increased in persons with DS. It is concluded that healthy DS persons of older age show extensive biochemical abnormalities suggesting a compromised homocysteine metabolism, an activated cell-mediated immune response and an enhanced turnover of dopamine.