Leukocyte and plasma N-laurylsphingosine deacylase (ceramidase) in Farber disease.

Severe deficiency of acid ceramidase activity (4-5% of normal) was demonstrated in cultured skin fibroblasts, leukocytes and plasma from a 1-year-old boy who was diagnosed as being affected with Farber disease. Determination of ceramidase activity in plasma was achieved by a highly sensitive assay employing a ceramide substrate containing radiolabeled C12 N-acyl moiety (N-lauryl). The enzyme activity in the parents' leukocytes and plasma was found to be reduced to 18-47% of the respective normal values, and that determined in a plasma specimen from a patient with I-cell disease was about 4 times elevated above the normal level.

Prenatal diagnosis of I-cell disease in the first and second trimesters.

First trimester prenatal diagnosis of I-cell disease (1 case) was based on demonstration of profound deficiency of N-acetylglucosamine 1-phosphotransferase in chorionic villi and in cultured trophoblasts derived from the chorionic villus specimen. Deficiency of this enzyme in cultured amniotic fluid cells obtained via amniocentesis was the basis for prenatal diagnosis of I-cell disease in the second trimester (2 cases). In both procedures, the diagnosis was corroborated by the finding of intracellular deficiency and extracellular elevation of multiple lysosomal enzymes in the fetal cell cultures (trophoblasts and amniotic fluid cells), as well as a significant increase in several lysosomal enzyme activities in the maternal serum.

Detection of Krabbe disease using tritiated galactosylceramides with medium-chain fatty acids.

Galactocerebrosidase (galactosylceramidase) assays using tritiated galactosylceramides with saturated, medium-chain fatty acids (C6-C11) were found to be more sensitive and more reliable than the commonly used assays with long-chain and very long-chain substrates (C16-C26). Galactosylsphingosine (psychosine) was tritiated by a modification of the galactose oxidase-sodium borohydride method, and 19 galactosylceramides were synthesized by the direct coupling of galactosylsphingosine with fatty acids of varying lengths (C6 to C24). The highest specific activities of normal prenatal and postnatal enzyme preparations were obtained with the C6 and C8 derivatives, which were six and five times more sensitive, respectively, than the C16 substrate. The residual activities in enzyme preparations from fetuses and children with Krabbe disease were proportionally increased. Our experience indicates that these substrates can provide a sensitive and reliable means for the prenatal and postnatal detection of Krabbe disease.