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We have investigated developmental changes in activity for five enzymes associated with different cerebral metabolic systems in two separate strains of mice. The enzymes studied were acid beta-galactosidase, arylsulfatase A, cerebroside beta-galactosidase, cerebroside sulfotransferase, and glutamate decarboxylase. The two strains of mice were C3H/SWV and ICR/SWV. We confirm the experiments of Meisler, Paigen, and colleagues showing higher acid beta-galactosidase activity throughout development in C3H mice. In addition we have demonstrated higher arylsulfatase A activity throughout development in C3H mice. The shape of the developmental curve for arylsulfatase A activity in brain in the two strains was similar. There were no differences in developmental changes of activity between the two strains for the other three enzymes studied.

Developmental changes in three enzymes associated with myelin lipids were studied in the shiverer mouse, a murine mutant showing a severe deficiency of CNS myelin. Age-related changes in cerebroside sulfotransferase (measured in brain) and arylsulfatase A and cerebroside B-galactosidase (measured in brain and liver) were the same for shiverer and control mice. The shiverer mouse, therefore, demonstrates a dissociation between the genetic mechanisms regulating myelination in the CNS and developmental changes in enzyme activities thought to be closely related to the synthesis of myelin. In addition, we found no defect in the shiverer mouse in the incorporation of glycine-labeled basic protein into CNS myelin, indicating an important metabolic difference between the morphologically similar shiverer and quaking mutants.

The detection of heterozygotes for MLD based on enzyme assays of a general population is highly unreliable. Twenty-three percent of controls and ARA activities below the levels found in some obligate heterozygotes for MLD. This serious overlap problem precludes the use of ARA determinations in large screening programs to assign individuals into specific genetic categories. On the other hand, intrafamily analysis of ARA activity offers the possibility of accurately determining heterozygotes for MLD. Sixteen children of parents heterozygous for MLD had ARA activities which clearly categorized them as either homozygous affected, heterozygous, or normal. The wide range of ARA activity found in controls and heterozygotes for MLD appeared to result from the presence of multiple allelic mutations at the ARA locus. One of these mutations leads to a low ARA activity and when present in an individual who is heterozygous for MLD may lead to overlap of his total activity with that of some homozygous affected individuals. This low ARA activity mutation can be recognized by alterations in the multiple molecular forms of ARA activity separated by analytical isoelectric focusing electrophoresis.

Arylsulfatase A (ARA) can be separated into six to eight individual enzymatic bands of activity by isoelectric focusing on cellulose acetate membranes. The residual ARA activity in juvenile metachromatic leukodystrophy (MLD) has a single band of activity with apI of 5.5, whereas the residual ARA in the late infantile form of MLD has three bands of activity with pI range of from 5.4 to 5.8. The technique of isoelectric focusing on cellulose acetate membranes demonstrates enzymatic differences which can be correlated with the clinical form of the disease.