Krabbe's globoid cell leucodystrophy. Studies on galactosylceramide beta-galactosidase and non-specific beta-galactosidase of leucocytes, cultured skin fibroblasts, and amniotic fluid cells

Niemann-Pick disease type C with enhanced glycolipid storage. Report on further case of so-called lactosylceramidosis

A case of infantile neurovisceral disease was classified according to the morphological and chemical analysis of fixed tissue as a chemically different type of Niemann-Pick disease (NPD) type C, with glycolipids dominating the storage process. The diagnosis was reached on the basis of massive accumulation of neutral glycolipids in visceral storage elements (hepatocytes and macrophages) as an outstanding feature of lipid histochemistry. Chemical lipid analysis corroborated the findings by detecting a manyfold increase of glucosyl ceramide, lactosyl ceramide, ceramide trihexoside and GM3 ganglioside. In addition, macrophages contained variable quantities of sphingomyelin. The brain showed slightly increased quantities of lactosylceramide (Slower fraction) and glucosyl ceramide. Apart from the classical neuronal storage changes there was also marked neuroaxonal dystrophy. In terms of quality, the glycolipid spectrum was comparable to that of NPD type C, in terms of quantity, the changes were consistent with those in so-called lactosylceramidosis, which, however, was reclassified as NPD type C only recently. In our view, the present case is the second published observation of lactosylceramidosis classifiable as a glycolipid (GL) variety of NPD type C in which the normally considerable tendency to glycolipid storage is further enhanced while the storage of sphingomyelin is less expressed.

Application of a galactosylceramidase microassay method to early prenatal diagnosis of Krabbe's disease

An enzymatic microassay method was devised to determine galactosylceramidase activities of microsamples prepared from primary cultures of amniotic fluid cells. A piece of freeze-dried cell mass (0.5--1 microgram dry weight) prepared from a colony on the bottom plate of a culture flask, was weighed and incubated in 4.02 microliter of the assay mixture. A small amount of galactose hydrolyzed from galactosylceramide was amplified about 10 000-fold and determined by using an enzymatic amplification reaction, NAD cycling. Microsamples were also prepared from freeze-dried leukocytes and skin fibroblasts. The present method was applied to prenatal diagnosis using amniotic cells as a sample in a case of high-risk pregnancy for Krabbe's disease. The result was confirmed by analysis of fibroblasts and organs from the aborted fetus.

Studies on pyrophosphate diesterase activity in cultured human fibroblasts: a deficiency in Niemann-Pick disease

Fibroblast phosphodiesterase activity was studied using 4-methylumbelliferyl pyrophosphate diester as substrate. Release of the fluorogen, 4-methylumbelliferone, was found to be dependent on acid phosphatase activity, normally present in excess in crude cell extracts. Phosphodiesterase activity had an acid pH optimum, was deficient in Niemann-Pick disease fibroblasts, and, when assayed in the presence of exogenous acid phosphatase, had an identical electrofocusing profile to that of sphingomyelinase. These findings suggest that 4-methylumbelliferyl pyrophosphate diesterase and acid sphingomyelinase activities are dependent on the same enzyme.

Prenatal diagnosis of Krabbe disease

Krabbe disease was diagnosed prenatally in Göteborg (Sweden) and Lyon (France) by assaying the cerebroside-beta-galactosidase activity with galactosylceramides and lactosylceramides as substrates in cultivated amniotic fluid cells. Altogether, 48 pregnancies at risk were monitored between 1972 and 1980. Ten pregnancies at risk were terminated because of a predicted affection of the fetus. Biochemical examination of material available from 7 of the 10 abortuses confirmed the diagnoses. All the remaining 36 pregnancies ended in the birth of a healthy infant. The study showed that prenatal diagnosis of Krabbe disease is difficult because of the relatively high residual cerebroside-beta-galactosidase activity in some affected fetuses. Except for the large biological variation, the enzyme activity was sensitive to variation in cultivation conditions and differed strikingly between morphologically different cell types. These two factors were controlled by including control cell samples cultivated under identical conditions and by relating the cerebroside-beta-galactosidase activity to that of two marker enzymes. The biological variation was investigated further by measuring the cerebroside-beta-galactosidase activity in cultured skin fibroblasts from infants with Krabbe disease and from their parents. Results obtained in 18 unrelated patients with Krabbe disease, 26 obligate heterozygotes and 63 controls showed a wide range of variation in enzyme activity in the controls, a large overlap between the controls and obligate heterozygotes, and a high residual activity in some patients. Nevertheless, a high residual activity in a patient was combined with a relatively high enzyme activity in the two parents. In the light of the above findings and deliberations, it appears warranted to conclude that laboratories with experienced personnel can make a reliable prenatal diagnosis of Krabbe disease and that the examination should be offered to all known couples at risk.

Spectrophotometric and fluorimetric assays of galactocerebrosidase activity, their use in the diagnosis of Krabbe's disease

Derivatives of galactocerebroside were prepared containing coloured (w-2,4,6-trinitrophenylaminolauric acid) or fluorescent (11-(9-anthroyloxy) undecanoic acid) fatty acid moieties.. These cerebrosides were used as substrates for galactocerebrosidase activity. By overcoming problems associated with the radioactively labelled substrates normally used, yet retaining good enzyme-substrate specificity, these derivatives provided useful and reliable alternative substrates for galactocerebrosidase activity. Enzyme activities in whole extracts of brain, liver, fibroblasts and cultured amniotic fluid cells were compared, using as substrates the novel cerebrosides as well as [3H]galactocerebroside. Good correlation of activities was obtained. In extracts derived from patients with Krabbe's disease marked deficiency of galactocerebrosidase activity was observed with each substrate, whereas extracts from heterozygous carriers exhibited a partial reduction in enzyme activity. The results show that these coloured and fluorescent galactocerebrosides may be used with confidence in the diagnosis and carrier detection of Krabbe's disease.

The interrelations between high- and low-molecular weight forms of normal and mutant (Krabbe-disease) galactocerebrosidase

Galactocerebrosidase (beta-d-galactosyl-N-acylsphingosine galactohydrolase; EC 3.2.1.46) activity of brain and liver preparations from normal individuals and patients with Krabbe disease (globoid-cell leukodystrophy) have been separated by gel filtration into four different molecular-weight forms. The apparent mol.wts. were 760000+/-34000 and 121000+/-10000 for the high- and low-molecular-weight forms (peaks I and IV respectively) and 499000+/-22000 (mean+/-s.d.) and 256000+/-12000 for the intermediate forms (peaks II and III respectively). On examination by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, the high- and low-molecular-weight forms revealed a single protein band with a similar mobility corresponding to a mol.wt. of about 125000. Antigenic identity was demonstrated between the various molecular-weight forms of the normal and the mutant galactocerebrosidases by using antisera against either the high- or the low-molecular-weight enzymes. The high-molecular-weight form of galactocerebrosidase was found to possess higher specific activity toward natural substrates when compared with the low-molecular-weight form. It is suggested that the high-molecular-weight enzyme is the active form in vivo and an aggregation process that proceeds from a monomer (mol.wt. approx. 125000) to a dimer (mol.wt. approx. 250000) and from the dimer to either a tetramer (mol.wt. approx. 500000) or a hexamer (mol.wt. approx. 750000) takes place in normal as well as in Krabbe-disease tissues.

Diagnosis of Niemann-Pick disease using a simple and sensitive fluorimetric assay of sphingomyelinase activity

Phosphodiesterase activity of cultured cells was determined with bis-(4-methylumbelliferyl) phosphate as substrate. In the presence of Triton X-100 an acid component was evident and results indicated that this enzyme was identical with sphingomyelinase. Acid phosphodiesterase activity was specifically inhibited by sphingomyelin. In fibroblasts from patients with Niemann-Pick diseases types A, B and C, acid phosphodiesterase activity was deficient whereas neutral activity was normal. Neutral activity could, however, be removed by acid precipitation or by binding to DEAE-cellulose. Hence a simple and sensitive fluorimetric method is described for the assay of sphingomyelinase activity in the diagnosis of Niemann-Pick disease.

Use of a chromogenic substrate for the diagnosis of Krabbe's disease, with special reference to its application in prenatal diagnosis

A chromogenic substrate, 2-hexadecanoylamino-4-nitrophenyl-beta-D-galactopyranoside, has recently been described for the diagnosis of Krabbe's disease. Hydrolysis of this substrate by extracts of cultured cells and tissues was compared with the activities of lactocerebrosidase I and non-specific beta-galactosidase. Under appropriate conditions, hydrolysis of the chromogenic analogue was markedly reduced in extracts of cultured amniotic fluid cells and skin fibroblasts derived from cases of Krabbe's disease. Activity was also markedly deficient in extracts of Krabbe's brain, although only a partial reduction was measured in liver extracts. Generally activities were higher in tissues of fetal origion. Unfortunately, the new analogue proved less specific and less sensitive than the natural substrates used to diagnose Krabbe's disease. Consequently, the analogue does not provide a satisfactory alternative substrate for the prenatal diagnosis of Krabbe's disease.

The use of natural and artifical substrates in the prenatal diagnosis of Krabbe's disease

Krabbe's disease was diagnosed prenatally using cultured amniotic fluid cells and the diagnosis confirmed using fetal brain, liver and cultured fetal skin fibroblasts. The enzyme defect was demonstrated by assay of galactocerebrosidase and lactocerebrosidase I, and by hydrolysis of the chromogenic analogue, 2-hexadecanoylamino-4-nitrophenyl-beta-D-galactopyranoside. The relative merits of the three diagnostic methods are discussed.

Studies on sphingomyelinase activity in cultured cells and leucocytes

Using both [3H]ceramide-sphingomyelin and [14C]methyl choline-sphingomyelin as substrate, enzyme activity was determined in skin fibroblasts, cultured amniotic fluid cells and leucocytes. Sphingomyelinase activities of fibroblasts from two patients with Niemann-Pick disease were about 1% of the mean control values (22.9 nmol/h/mg protein and 65.6 nmol/h/mg protein, with [3H]sphingomyelin and [14C]sphingomyelin respectively). Leucocyte sphingomyelinase activity is much lower than that of cultured cells. Optimum sphingomyelinase activity of cultured cells is at pH 5.0 and the apparent Km values are 58 mumol/1 and about 200 mumol/1 for [3H]sphingomyelin and [14C]sphingomyelin respectively. These properties are similar to those for residual sphingomyelinase activity in Niemann-Pick fibroblasts.