Objective: Lysosomal enzyme deficiency results in an accumulation of undegraded material producing structural and functional disorders. Mucopolysaccharidosis is a group of disorders caused by an increase in glycosaminoglycans (GAG) (mucopolysaccharides). Mucopolysaccharidosis, while showing a low incidence, has some clinical manifestations that warrant early diagnosis in order to establish immediate therapeutical action. Although definitive diagnosis is based on quantification of the involved enzymatic activity, it is necessary to have easy to use analytical methods available when there is clinical suspicion of the disease.
Patients and methods: This study was made on a population of 632 clinically normal adolescents and children (one month to 18 years of age). In all cases a partial sample of urine to quantify glycosaminoglycans and creatinine expressed as the index GAG/creatinine (mg/mmol) was collected. In a reduced group of 27 people a 24-hour urine sample was collected. Determination of glycosaminoglycan levels was performed with a colorimetric reaction with 1,9-dimethylmethylene blue (DMB). Optimal condition of pH, wavelength and reaction time were established. The values found to be optimal for quantification were defined as pH 4.0, wavelength 528 nm and a reaction time of five minutes. Intra- and inter-assay coefficients of variation were less than 5%.
Results: Validity of the partial urine sample was established by obtaining a linear correlation between the 24 hour urine sample and the partial urine sample with a correlation coefficient of r = 0.89 (p < 0.0001). The results obtained have allowed the establishment of normal values ranging from an index GAG/creatinine of 8.70 mg/mmol in the group aged 1 to 2 years to 1.34 mg/mmol in the group 17 to 18 years of age, with a distribution of intermediate ages adjusted to a logarithmic function. There was a clear difference in the values obtained in urine of patients with clinical suspicion of mucopolysaccharidosis.
Conclusions: Modifications in the spectrophotometric method using DMB as a colorant for quantification of glycosaminoglycans are presented. The feasibility, easy application and sensibility of this method, condition required for its widespread use, are confirmed. Normal reference values from a healthy population have been obtained and shown to be age dependent.