ARSA and metachromatic leukodystrophy: MLD is often suspected when typical abnormalities on brain MRI are found and confirmed by measuring ASA activity in leukocytes (or fibroblasts) and sulfatide levels in urine and genetic testing.4 It is also important to evaluate for ASA pseudodeficiency, which is present in 1%–2% of Caucasians and up to 17.4%–25.6% of the Tunisian population.7,8 In ASA pseudodeficiency, ASA activity when measured in vitro is significantly reduced (5%–15% of normal enzyme levels) due to 2 ARSA variants, without clinical manifestations.