HHEX and metachromatic leukodystrophy: Regarding the CSF biomarkers, significant difference (p = 0.03) was found between the groups for HEX activity, which mean value was 112.4 ± 57.3 nmol/h/mL in the GD group versus 208.2 ± 34.7 nmol/h/mL observed in the MLD group.