[Biochemical alterations in patients with Down syndrome]

Down syndrome is a chromosome abnormality with specific clinical symptoms and mental retardation caused by trisomy of chromosome 21. The basic genetic change cannot be cured, the control of the associated symptoms, however, may improve the patients' quality of life.

Authors studied the possible correlations between the Down-specific genes and the related biochemical changes. Expression of superoxide dismutase, cystathionine-beta-synthase and S100 protein was investigated. Further aim of the study was to determine the total serum antioxidant capacity (transferrin, ferritin, total protein, albumin and bilirubin) along with the extracellular antioxidants as well as concentrations of homocysteine, folic acid, and vitamin B 12 . To assess the vascular damage, the activity of NAG and S100B level was measured.

Standard laboratory methods were used to determine the antioxidant capacity (Stocks, 1974), homocysteine (HPLC), folic acid (capture, IMX-Abbott), vitamin B 12 (MEIA, IMX-Abbott), S100 B protein (chemiluminescence sandwich immunoassay) levels, and N-acetyl-beta-D-glucosaminidase (spectrophotometry).

Plasma homocysteine value proved to be lower in 7 of the 30 and higher in 6 of the 30 patients studied than the reference range. Plasma homocysteine was found 95 +/- 21% of the reference value. Relative value of plasma folic acid - expressed in percent of the normal value - was 85 +/- 51%, and that of B 12 was 78 +/- 30%. Deficiency of folic acid was detected in 2 of the 30, decreased level of B 12 in 2 of the 30 patients enrolled. No difference was found in antioxidant activity values between Down syndrome patients and healthy controls, however, neither of them reached the adult reference range. S100 protein concentration of 4-8 times higher values (average value: 0.68 +/- 0.27 microg/l) than upper limit of the reference range was observed (> 1 year: > 0.15 microg/l). Mean value of serum N-acetyl-beta-D-glucosaminidase remained within the reference range (10-30 U/l). No statistically significant correlation between the antioxidant activity and N-acetyl-beta-D-glucosaminidase values could be observed.

The lower homocysteine, folic acid and B 12 values may be considered as the consequence of an increased cystathionine-beta-synthase activity ("atheroma free model"). There was no significant alteration in antioxidant activity level. It can be supposed that the hydrogene peroxide produced due to increased expression of superoxide dismutase is metabolized by the induced glutathione-peroxidase and catalase keeping by this the balance of the antioxidant system. This hypothesis is supported by the normal N-acetyl-beta-D-glucosaminidase values not indicating any vascular damage. The high S100 values, however, reflect certain brain damage which shows a progress with the age. Based on these experiences, regular control of these parameters is recommended. Furthermore authors think that folic acid supplementation is indicated in order to improve the patients' learning capacity, inhibit the development of Alzheimer symptoms and improve the quality of life.