FIRST REPORT OF CONGENITAL OR INFANTILE CATARACT IN DERANGED PROTEOGLYCAN METABOLISM WITH RELEASED XYLOSE

Aim-To investigate the chemical pathology in the blood and lens, in ca ses of congenital or infantile cataract in children excreting predomin antly non-reducing carbohydrates in urine. Methods-Urine samples from children with congenital or infantile cataract, and age and sex-matche d controls, were analysed for (i) inherited errors of metabolism, (ii) paper chromatography of sugars, (iii) spectrophotometric assay of gly cosaminoglycans (GAG), (iv) cetyl trimethyl ammonium bromide test, (v) electrophoresis using Alcian blue, (vi) ion exchange chromatography w ith IR 120 resin, and (vii) HPLC for xylose. Blood and lens material w ere also tested for GAG fragments and xylose. beta Glucuronidase was a ssayed in lymphocytes and urine. Results-Of 220 children of both sexes below 12 years of age, with congenital or infantile cataract treated in Sankara Nethralaya, Madras, India, during a period of 2 years, 145 excreted fragments of GAG (heparan and chondroitin sulphates) in their urine. There was no such excretion among the control group of 50 chil dren. The same was found accumulated in the blood and lenses of affect ed children. In addition, xylose was present in small amounts in the u rine and blood and xylitol was present in the lens. There was a signif icant elevation in the activity of beta glucuronidase in lymphocytes a nd urine, when compared with normals. All the above findings suggest d eranged proteoglycan metabolism. As the urine contained mostly GAG fra gments and very little xylose, Benedict's reagent was not reduced. Thi s ruled out galactosaemia. Conclusion-An increase of beta glucuronidas e activity might have caused extensive fragmentation of GAG with resul tant accumulation in the blood and lens and excretion in urine. Small amounts of xylose may have come from xylose links between GAG and core protein of proteoglycans. Owing to their polyanionic nature, GAG frag ments in the lens might abstract sodium, and with it water, thereby in creasing the hydration of the lens. Excessive hydration and the osmoti c effect of xylitol from xylose might cause cataract. While corneal cl ouding has been reported in inborn acid mucopolysaccharidosis, congeni tal or infantile cataract with deranged metabolism of proteoglycans (a cid mucopolysaccharide-xylose-protein complex) is reported in children for the first time.