ARSA and metachromatic leukodystrophy: When tested in primary cultured fibroblasts from MLD patient (ASA-I179S) and controls (ASA-WT), these small molecules with curve class 2.4 failed to produce any significant enhancement of ASA activity in primary control (ASA-WT) and MLD patient (ASA-I179S) fibroblasts (Fig.9C–F).