[(14)C]
Stearic acid-labeled
cerebroside sulfate (CS) was presented to cultured skin fibroblasts in the media. After endocytosis into control cells 86% was readily metabolized to
galactosylceramide,
ceramide, and
stearic acid, which was reutilized in the synthesis of the major
lipids found in cultured fibroblasts. Uptake and metabolism of the [(14)C]CS into cells from typical and atypical patients and carriers of
metachromatic leukodystrophy (MLD),
Krabbe disease, and
Farber disease were observed. Cells from patients with late infantile MLD could not metabolize the CS at all, while cells from an adult MLD patient and from a variant MLD patient could metabolize approximately 40 and 15%, respectively, of the CS taken up. These results are in contrast to the in vitro results that demonstrated a severe deficiency of
arylsulfatase A in the late infantile and adult patient and a partial deficiency (21-27% of controls) in the variant MLD patient. Patients with
Krabbe disease could metabolize nearly 40% of the
galactosylceramide produced in the lysosomes from the CS. This is in contrast to the near zero activity for
galactosylceramidase measured in vitro. Carriers of
Krabbe disease with
galactosylceramidase activity near half normal in vitro and those with under 10% of normal activity were found to metabolize
galactosylceramide in cells significantly slower than controls. This provides a method for differentiating affected patients from carriers with low
enzyme activity in vitro. Cells from patients with
Farber disease could catabolize only approximately 15% of the
ceramide produced from
galactosylceramide. This technique provides a method for the identification of typical and atypical patients and carriers of three
genetic diseases using one substrate.