Screening for mucopolysaccharide disorders with the berry spot test

Abstract

The Berry spot test, based on metachromatic straining of urinary acid mucopolysaccharides (MPS), is widely used to screen for inherited MPS disorders. During a 5-year period over 6000 specimens from a variety of patients were tested as part of routine metabolic screening. Urine was applied to filter paper, stained with toluidine blue, and destained by washing in acetic acid. Over 90% of specimens showed no metachromasia. Quantitative measurements of hexuronic acid were carried out on all specimens with positive tests using the borate modification of the Dische carbazole reaction. Molecular species were identified following electrophoresis on cellulose acetate and staining with alcian blue. Mean concentration of hexuronic acid in specimens with + reaction was 113 +/- 67 mumol/L. Only chondroitin sulfate A/C was identified by electrophoresis. Hexuronic acid concentration in strongly positive + + + specimens ranged from 335-1546 mumol/L, and heparan sulfate, dermatan sulfate or both were identified. Additional specimens were obtained from patients with + + + reactions and from 15 control children with negative spot tests. Excretion of hexuronic acid by + + + patients was 175-258 mumol/day (84-181 mmol/mol creatinine) compared to 41 +/- 36 mumol/day (10 +/- 5 mmol/mol creatinine) by control subjects. Urine testing simplifies the differential diagnosis by demonstrating the biochemical defect and pointing to the probable enzyme defect. The screening test has been highly effective in identifying patients with MPS disorders.