First-trimester diagnosis of metachromatic leucodystrophy

Two pregnancies at risk for late infantile metachromatic leucodystrophy were monitored by assaying arylsulphatase A at 0 degrees C in homogenates of chorionic villi. In one, the very low activity recorded indicated the fetus to be affected, and this was confirmed by demonstration of low arylsulphatase A activity in cultured villi and cultured fetal fibroblasts after termination. In the other pregnancy, normal activity was found in the villi and the pregnancy is continuing. This simple chromogenic assay appears to be reliable for first-trimester diagnosis of metachromatic leucodystrophy. However, there is a probability of mis-diagnosis if the standard assay at 37 degrees C is used.