Elevated sulfatide excretion in heterozygotes of metachromatic leukodystrophy: dependence on reduction of arylsulfatase A activity.
Sulfatide excretion in urine and arylsulfatase A (ASA) activity in leukocytes were determined in 10 homozygotes of metachromatic leukodystrophy (MLD), 7 obligate and 5 facultative MLD heterozygotes, 6 low ASA subjects (not related to MLD homozygotes), and in 9 controls. As compared to controls (sulfatides: 0-2 nmol/mg lipid; ASA: 101-287 nmol p-nitrocatechol/mg protein/hr), MLD homozygotes displayed highly increased sulfatide excretions (27-280 nmol) and low residual ASA activities (0-13 nmol). Of 12 MLD heterozygotes (ASA: 18-87 nmol) 10 showed increased sulfatides (3-24 nmol). All heterozygotes with ASA activity < 60 nmol (n = 8) had elevated sulfatide excretions (4-24 nmol). Thus, reduction of ASA activity below 40% of the mean value of controls seems to be the critical threshold for elevated sulfatide excretion in MLD heterozygotes. The low ASA subjects (ASA in the heterozygote range) excreted sulfatides in the control range, even those with ASA activities < 60 nmoles (n = 3; including a definite homozygote for ASA-pseudodeficiency; ASA:25 nmol). Statistical evaluation of sulfatide excretion and ASA activity in all subjects (n = 37) revealed a significant inverse relation (Spearman rank correlation; R = 0.8278, P < 0.001). The finding of elevated sulfatide excretion in certain MLD heterozygotes might point to increase of sulfatides also in the nervous system.