Use of leukocytes in diagnosis of Krabbe disease and detection of carriers.

The optimal conditions for the assay of the cerebroside-beta-galactosidase deficiency in Krabbe disease were studied. Labelled galactosylceramides and lactosylceramides isolated from natural sources were both suitable substrates provided that the lipophilic moieties were identical in labelled and unlabelled portions. Galactosylceramides and lactosylceramides with uniform fatty acid compositions were also tested. The highest specific cerebroside-beta-galactosidase activities were obtained with N-palmitoyl galactosyl- and lactosylceramides. The chromogenic substrate 2-hexadecanoyl-amino-4-nitrophenyl-beta-D-galactopyranoside (HNGal) was shown to be an unreliable substrate requiring large amounts of enzyme protein and giving false normal results. Krabbe disease was diagnosed in 45 patients. With galactosylceramides as substrates the residual cerebroside-beta-galactosidase activity was 7%, with lactosylceramides 8%, and there was no overlap in enzyme activity between the 45 patients and 42 parents. Approximately 50% of the obligate carriers had values within the range for the normal controls, independently of which substrate was used.