Prenatal diagnosis of mucopolysaccharidosis I: A special difficulty arising from an unusually low enzyme activity in mother's cells.

We investigated a case (I.I.) of the severe form of mucopolysaccharidosis I (Hurler syndrome). Prenatal diagnosis was requested by the parents and the next pregnancy was monitored. We report here a special difficulty arising in this diagnosis due to the low enzyme activity in the mother's cells (10-15 per cent of controls) as well as in amniotic cells and would like to stress the need for studying the index case as well as the parents' enzyme activities in order to be prepared for possible difficulties at prenatal analysis.