Intrauterine fetal death due to Farber disease: case report

We report a case of Farber disease in a fetus who died in utero at a gestational age of 29 weeks. Macroscopic examination showed moderate postmortem changes in a microcephalic female fetus (46,XX) with mild internal hydrops, two vessels in the umbilical cord, and a moderately enlarged, relatively well-preserved spleen. Microscopic examination showed foamy cells in the spleen. Electron microscopic examination revealed the presence of Farber bodies within these foamy cells. Enzyme studies of the fetus were not possible because all tissues were formalin fixed. Lipids were extracted from formalin-fixed tissues and increased levels of ceramide and the presence of hydroxyceramide in tissue of the spleen, liver, and lung were found. Glucosylceramide was not increased excluding saposin-precursor-deficiency. Because of these findings, both parents were tested for acid ceramidase activity in their leukocytes. They both had markedly reduced enzyme activity consistent with heterozygosity for Farber disease. To the best of our knowledge, this is the first published case of Farber disease in Dutch nonconsanguineous parents.

Wolman disease successfully treated by bone marrow transplantation

Wolman disease is characterized by severe diarrhea and malnutrition leading to death during infancy. Lysosomal acid lipase deficiency is the cause of the symptoms and signs. It is inherited in an autosomal recessive manner. All Wolman disease patients have adrenal gland calcification. Previous therapeutic attempts have failed to provide remission. We report successful long-term bone marrow engraftment in a patient with Wolman disease resulting in continued normalization of peripheral leukocyte lysosomal acid lipase enzyme activity. Diarrhea is no longer present. Now, at 4 years of age, this patient is gaining developmental milestones. Cholesterol and triglyceride levels are normal. Liver function is normal. This is the first long-term continued remission reported for Wolman disease.

Discrimination between metachromatic leukodystrophy and pseudo-deficiency of arylsulfatase A by restriction digest of amplified gene fragments

Mutations causing metachromatic leukodystrophy and pseudo-deficiency were detected in the arylsulfatase A gene by methods based on different wild-type and mutant restriction sites. After polymerase chain reaction amplification of fragments of the arylsulfatase A gene and digestion by the appropriate endonuclease, the mixtures were separated by polyacrylamide gel electrophoresis and visualized by ethidium bromide staining. The common splice mutation in intron 2 (459 + 1G-->A) causing, in homozygosity, late-infantile metachromatic leukodystrophy and the common missense mutation in exon 8 (P426L) causing, in homozygosity, adult or juvenile metachromatic leukodystrophy were found to abolish Bst NI and Aci I sites, respectively. The polyadenylation pseudo-deficiency mutation (1619A-->G) was found to create a Mae III restriction site. The N-glycosylation pseudo-deficiency mutation (N350S) does not produce or destroy any known restriction site, and in this case, introduction of a single nucleotide mismatch in one of the primers enabled the authors to create a Bfa I site in the mutant allele.

Mucolipidoses II and III variants with normal N-acetylglucosamine 1-phosphotransferase activity toward alpha-methylmannoside are due to nonallelic mutations

Normal N-acetylglucosamine 1-phosphotransferase activity toward mono- and oligosaccharide acceptor substrates was detected in cultured skin fibroblasts from mucolipidoses II and III patients who were designated as variants (one of four mucolipidosis II and three out of six mucolipidosis III patients examined). The activity toward natural lysosomal protein acceptors was absent or deficient in cell preparations from all patients with classical as well as variant forms of mucolipidoses II and III. Complementation analysis, using fused and cocultivated mutant fibroblast combinations, revealed that, while cell lines with variant mucolipidosis III constituted a complementation group distinct from that of classical forms of mucolipidoses II and III, the variant mucolipidosis II cell line belonged to the same complementation group as did the classical forms. In contrast to the mutant enzyme from variant mucolipidosis III patients that failed to recognize lysosomal proteins as the specific acceptor substrates, the activity toward alpha-methylmannoside in the variant mucolipidosis II patient could be inhibited by exogenous lysosomal enzyme preparations (bovine beta-glucuronidase and human hexosaminidase A). These findings suggest that N-acetylglucosamine 1-phosphotransferase is composed of at least two distinct polypeptides: (1) a recognition subunit that is defective in the mucolipidosis III variants and (2) a catalytic subunit that is deficient or altered in the classical forms of mucolipidoses II and III as well as in the mucolipidosis II variant.

Stimulation of GM3 ganglioside sialidase activity by an activator protein in patients with mucolipidosis IV and controls

An activator protein that stimulates the enzymic hydrolysis of sialic acid from gangliosides by ganglioside sialidase was fractionated from human liver. This fraction was distinct from those stimulating the hydrolysis of galactose from GM1 ganglioside by beta-galactosidase and the hydrolysis of N-acetylgalactosamine from GM2 ganglioside by hexosaminidase A. This fraction was highly specific for the hydrolysis of sialic acid from GM3 ganglioside, and was equally effective in fibroblasts from patients with mucolipidosis IV and in fibroblasts from controls.

Detection of kinetically abnormal argininosuccinate synthase in neonatal citrullinemia by conversion of citrulline to arginine in intact fibroblasts

The apparent Km values of argininosuccinate synthase toward citrulline and aspartate were significantly increased in cultured skin fibroblasts from one patient with neonatal citrullinemia, whereas, those determined in cells from three other patients were within the normal range. The abnormal apparent Km of the mutant enzyme toward aspartate was determined by a ureagenesis assay system (0.14 mmol/l as compared with 0.010-0.018 mmol/l for the normal enzyme), and the abnormal values toward citrulline were measured by both arginine synthesis (6.1 mmol/l as compared with 0.21-0.26 mmol/l for the normal enzyme) and ureagenesis (0.63 as compared with 0.043-0.067) assay systems.

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.

First trimester maternal serum lysosomal enzymes: implications for carrier testing and prenatal diagnosis

Carrier detection for lysosomal storage diseases is sometimes possible by evaluating maternal serum levels of specific enzymes. However, lysosomal enzymes (LE) can be modified by maternal hormonal changes in pregnancy or embryonic contributions. Maternal serum was obtained prospectively in the follicular phase and at 2-5 and 7-11 weeks after conception from 13 infertility patients with precisely known ovulation dates. Eleven enzyme activities were determined fluorimetrically using 4-methylumbelliferyl substrates. Using repeated measures ANOVA, alpha-N-acetyl-glucosaminidase (p less than 0.05), hexosaminidase A (p less than 0.005) and hexosaminidase A and B (p less than 0.005) increased during the first trimester, and 8 enzymes did not change significantly. Our data show differing patterns of LE in the first trimester. These may be explained by: (1) variability of maternal reaction to hormonal changes of pregnancy, or (2) variable embryonic contributions suggesting differential ontogeny and placental transfer of these enzymes. The increase in levels of the 3 specific LE in maternal serum may interfere with the accuracy of carrier testing in early pregnancy, but pregnancy should not interfere with the other 8.

Maternal serum hexosaminidase A in pregnancy: effects of gestational age and fetal genotype

The diagnostic usefulness of sulfated fluorogenic substrates in carrier detection of Tay-Sachs disease in serum during pregnancy was assessed by testing coded samples. Gradual increase in serum hexosaminidase activities toward these substrates was observed throughout pregnancy in both carrier and non-carriers of the Tay-Sachs gene, but absolute discrimination between the 2 genotypes could not be achieved even when values were compared within the same gestational age. Examination of isolated isozyme fractions with the sulfated substrates showed that the increased activities during pregnancy were due to a genuine increase in hexosaminidase A and not associated with the elevation of hexosaminidase I (or P), which was evident only with unsulfated substrates. The extent of the increase was influenced by the genotype of the fetus as indicated by higher values in pregnant carriers who carried non-carrier fetuses. We conclude that determination of serum hexosaminidase A during pregnancy by sulfated fluorogenic substrates may have a prenatal diagnostic value when used in obligate heterozygotes for Tay-Sachs disease, but is unreliable for screening purposes.

First trimester prenatal evaluation for I-cell disease by N-acetyl-glucosamine 1-phosphotransferase assay

First trimester prenatal diagnosis was offered to a couple at risk for having a child with I-cell disease (mucolipidosis II). The prenatal evaluation was based for the first time on examination of N-acetylglucosamine 1-phosphotransferase activity, deficiency of which is the primary biochemical defect in both I-cell disease and pseudo-Hurler polydystrophy (mucolipidosis III). Heterozygote levels of this enzyme activity were determined in chorionic villi obtained at 9 weeks of gestation, as well as in cultured trophoblasts derived from this specimen, and led to the diagnosis of an unaffected fetus. This procedure has advantages over that based on detection of abnormal intracellular-extracellular distribution of lysosomal enzyme activities, which is expressed only in homozygotes and fully expressed only in cell culture specimens.

Altered molecular size of N-acetylglucosamine 1-phosphotransferase in I-cell disease and pseudo-Hurler polydystrophy

The size of the mutant N-acetylglucosamine 1-phosphotransferase in Golgi membranes from fibroblasts of patients with I-cell disease and classical pseudo-Hurler polydystrophy, which comprised one complementation group characterized by deficiency towards both artificial and natural acceptor substrates, was significantly smaller than the normal enzyme, 151-174 kDa compared with 225-278 kDa. The size of the mutant enzyme from cell lines of patients with variant forms of pseudo-Hurler polydystrophy, which comprised another complementation group characterized by normal activity towards mono- and oligo-saccharide substrates, was significantly larger than the normal enzyme, ranging from 321 to 356 kDa in two families and from 528 to 547 kDa in a third family. These findings suggest that the mutations in I-cell disease and classical pseudo-Hurler polydystrophy result in a missing enzyme component, which renders the enzyme catalytically inefficient toward any type of acceptor substrate. In contrast, the mutations in the variant forms of pseudo-Hurler polydystrophy produce a larger enzyme molecule which is active toward small substrates but is incapable of binding natural lysosomal glycoprotein substrates.

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.

Lysosomal enzyme activities in fresh and frozen chorionic villi and in cultured trophoblasts

Fifteen lysosomal enzyme activities were compared in 14 presumed normal chorionic villus specimens that were each divided, processed and analyzed as fresh tissue, tissue frozen for 1 week, and cultures established from minced whole villi. Most of the activities determined in the chorionic villus tissue were not affected significantly by freezing. However, activities for most enzymes were significantly different from those determined in the cultured cells. Our experience with first trimester prenatal evaluations for several lysosomal disorders showed that the limited amount of tissue obtained is not always sufficient for thorough analysis and thus, cultured trophoblasts derived from the tissue specimen should also be examined. The results of this study stress the importance of using appropriate tissue-type and cell-type controls to establish the normal range in the respective analyses.

Molecular size of N-acetylglucosaminylphosphotransferase and alpha-N-acetylglucosaminyl phosphodiesterase as determined in situ in Golgi membranes by radiation inactivation

The radiation inactivation method was used to determine the molecular size of the two enzymes that participate in the synthesis of the phosphomannosyl recognition marker of lysosomal proteins. The determinations were carried out in situ, in Golgi membranes isolated from normal human placenta and cultured skin fibroblasts. A molecular size of 228 +/- 29 kDa was found for placental N-acetylglucosaminyl-phosphotransferase, and 129 +/- 11 kDa for placental alpha-N-acetylglucosaminyl phosphodiesterase. The values for the fibroblast enzymes were about 20% higher, 283 +/- 27 kDa and 156 +/- 14 kDa for the transferase and phosphodiesterase respectively. Triton X-100 had no effect on the molecular size of these enzymes.

Characterization of the mutant N-acetylglucosaminylphosphotransferase in I-cell disease and pseudo-Hurler polydystrophy: complementation analysis and kinetic studies

Complementation was examined among various types of I-cell disease and pseudo-Hurler polydystrophy by monitoring N-acetylglucosaminylphosphotransferase activity in multinucleated cells produced by fusing pair combinations of cultured skin fibroblasts. Patients with the classical forms of these disorders (5 I-cell disease and 3 pseudo-Hurler polydystrophy cell lines) comprised one complementation group and 5 cell lines from patients with variant forms of pseudo-Hurler polydystrophy comprised a distinct complementation group. In the first group, total or partial deficiency of the transferase activity was demonstrated with both natural (lysosomal enzymes) and artificial (alpha-methylmannoside) acceptor substrates with low Vmax but apparently normal Km values for the donor (UDP-GlcNAc) and acceptor (alpha-methylmannoside) substrates. The activity toward artificial substrate could be inhibited by adding exogenous lysosomal enzyme preparations to the reaction mixture. In the second group, the cells demonstrated deficiency of the transferase activity toward lysosomal enzyme acceptors but had normal activity toward alpha-methylmannoside acceptor and this activity could not be inhibited by the addition of exogenous lysosomal enzyme preparations. These findings suggest that N-acetylglucosaminylphosphotransferase is composed of at least two distinct subunits, a catalytic subunit which is absent or defective in the first complementation group, and a recognition subunit which is altered or deficient in the second group.

Diagnosis and carrier detection of Tay-Sachs disease: direct determination of hexosaminidase A using 4-methylumbelliferyl derivatives of beta-N-acetylglucosamine-6-sulfate and beta-N-acetylgalactosamine-6-sulfate

4-Methylumbelliferyl-6-sulfo-2-acetamido-2-deoxy derivatives of beta-D glucopyranoside and beta-D-galactopyranoside were prepared by direct sulfation of the commonly used unsulfated derivatives. Both sulfated substrates were highly specific for hexosaminidase A, and in fractionated serum, cells, and tissue preparations, less than 2.5% of these activities were associated with hexosaminidase B and the intermediate isozyme fractions. Serum and leukocytes from patients with infantile Tay-Sachs disease, including a patient with thermolabile hexosaminidase B, had less than 2% of noncarrier activities. Carrier values were clearly separated from those of noncarriers, and no problems were encountered in utilizing sera from pregnant women. The % hexosaminidase A values as derived from the ratio between the activities toward the sulfated and unsulfated substrates in the same specimen were comparable to those obtained by the heat-inactivation method (except for subjects with thermolabile hexosaminidase B) and may be helpful in genotype determination in borderline cases.

Correction of gamma-glutamyl transpeptidase deficiency in amniotic fluid of some cystic fibrosis fetuses by mixing with nondeficient fluids

The deficiency of gamma-glutamyl transpeptidase activity, which was evident in some but not all cystic fibrosis amniotic fluids, could be corrected by mixing with either normal fluids or nondeficient cystic fibrosis fluids. Incubation of any amniotic fluid for 20 min at 62 degrees C resulted in total loss of gamma-glutamyl transpeptidase activity, but the activity could be restored by mixing with untreated nondeficient fluids. In contrast, no restoration could be obtained by mixing with untreated deficient cystic fibrosis fluids. Dialysis of amniotic fluids did not diminish their corrective capacity. Only the transpeptidation reaction was corrected and no correction was observed for the hydrolysis or autotranspeptidation of gamma-glutamyl p-nitroanilide in the absence of the glycylglycine or methionine acceptor. Plasma specimens did not have any corrective activity, although their gamma-glutamyl transpeptidase activity could be restored after heat inactivation by mixing with untreated nondeficient amniotic fluids. No correction was found for aminopeptidase or disaccharidase activities. These findings suggest that the deficient cystic fibrosis amniotic fluids probably contain normal quantities of the gamma-glutamyl transpeptidase enzyme but lack a heat-labile nondialyzable activator that is necessary for its transpeptidation catalytic performance. An assay for this transpeptidase activator may provide a valuable approach to identify at least a subgroup of cystic fibrosis patients.

Radiometric assays of N-acetylglucosaminylphosphotransferase and alpha-N-acetylglucosaminyl phosphodiesterase with substrates labeled in the glucosamine moiety

The assay of fibroblast and leukocyte-N-acetylglucosaminylphosphotransferase with alpha-methylmannoside acceptor and commercially available UDP-[3H or 14C]N-acetylglucosamine donor was modified to yield low background and consequently high sensitivity and reliability comparable to those obtained with the synthetically made [beta-32P]UDP-N-acetylglucosamine donor. This was achieved by an additional elution step that removed free [3H or 14C]N-acetylglucosamine which appeared to be the breakdown product responsible for the high background. In addition, the [3H or 14C]N-acetylglucosamine-1-phospho-6-alpha-methylmannoside product of the transfer reaction was then isolated and, following desalting, could serve as a substrate for the assay of alpha-N-acetylglucosaminyl phosphodiesterase. Cell preparations of patients with I-cell disease and pseudo-Hurler polydystrophy demonstrated severe to moderate deficiency of transferase activity and normal phosphodiesterase activity toward the respective substrates labeled with 3H or 14C in the glucosamine moiety.

Thermal activation of hexosaminidase A in a genetic compound with Tay-Sachs disease

Increase in total hexosaminidase activity has been observed during heat treatment of serum and leukocyte specimens from a 1-year-old boy with cherry-red spot and severe and progressive mental and motor deterioration. The activity increased 40% in the first 40-70 min of incubation at 50 degrees C and pH 4.3, but declined thereafter and was only slightly above the initial activity in the final 2-3 h of incubation. Heat treatment of specimens from family members revealed very reduced rates of inactivation of hexosaminidase in the proband's father and some paternal relatives, whereas those of the mother and some maternal relatives were indistinguishable from those of Tay-Sachs carriers. Mixing experiments with enzyme preparations from the proband, normal controls and patients with Tay-Sachs disease resulted in additive values and did not support the possibility of inhibitor- or activator-related defect. Fractionation of heat-treated samples by ion exchange chromatography and electrophoresis, as well as examination of the separated fractions for their thermostability, have shown that hexosaminidase A is the activated component and hexosaminidases B, I1 and I2 are not affected. These findings suggest that the patient is a genetic compound and the apparent thermal activation is probably due to formation of hexosaminidase A from altered alpha-subunits produced by the paternal mutant alpha-allele and beta-subunits produced by the normal beta-alleles.

Mannosylation of glycoproteins and dolichol derivatives in fibroblasts from patients with cystic fibrosis

Increased incorporation of mannose into endogenous glycoprotein fractions has been found in whole cell lysates and crude membrane preparations of cultured skin fibroblasts from patients with cystic fibrosis (1.3-2.3-times normal) when GDP[14C]mannose served as the mannosyl donor. In contrast, the incorporation of mannose from GDPmannose into lipid fractions containing dolichol phosphate and dolichol pyrophosphate oligosaccharides as well as the incorporation of mannose from dolichol phospho[3H]mannose into both glycoproteins and dolichol derivatives were not significantly different among cell preparations from patients with cystic fibrosis and normal controls. Mannosyltransferase activity toward exogenous glycoproteins as well as the activities of soluble and membranous alpha-mannosidase and beta-mannosidase appeared to be normal and could not account for the observed differences. The altered incorporation of mannose into endogenous glycoprotein may reflect changes in glycosylation processes other than mannosylation.

Km defect in neuraminidase of dysmorphic type sialidosis with and without beta-galactosidase deficiency

Kinetic studies of 4-methylumbelliferyl neuraminidase activity were carried out in cultured skin fibroblasts from patients with various disorders of neuraminidase deficiency. Cell extracts from two patients with dysmorphic type sialidosis of infantile onset, with isolated deficiency of neuraminidase activity, and three patients with dysmorphic type sialidosis of juvenile onset, with combined deficiency of neuraminidase and beta-galactosidase activities, demonstrated 7-12 times higher apparent Km values than those of normal controls (1.0-1.5 mmol/l as compared with 0.12-0.15 mmol/l). The apparent Ki values for N-acetylneuraminic acid and colominic acid were also increased in the dysmorphic type (7-15 and 7-11 times the normal values, respectively). In contrast, in the normomorphic type, normal apparent Km and Ki values were found for 4-methylumbelliferyl neuraminidase activity in fibroblasts from one patient with isolated neuraminidase deficiency and two patients with combined deficiency of neuraminidase and beta-galactosidase. The altered kinetics in the dysmorphic cases indicates a primary defect in neuraminidase with a secondary deficiency of beta-galactosidase in patients with combined deficiency. It is not clear if the primary defect in the normomorphic cases involves a defect in neuraminidase other than a Km defect or if neuraminidase or both neuraminidase and beta-galactosidase deficiencies are secondary to another defect as yet undetermined.

Substrate-specificities of acid and alkaline ceramidases in fibroblasts from patients with Farber disease and controls

The specific activity of acid ceramidase (N-acylsphingosine deacylase, EC 3.5.1.23) was measured at pH4.5 in normal fibroblasts and in fibroblasts from patients with Farber disease and obligate heterozygotes. Greater activity was found when the synthetically made ceramide substrates contained shorter-chain fatty acids or higher content of double bonds. Acid ceramidase activities towards N-lauroyl- (C(12:0)), N-myristoyl- (C(14:0)) and N-palmitoyl- (C(16:0)) sphingosine (C(18:1)) were respectively about 38, 26 and 6 times higher than the activity towards the N-stearoyl (C(18:0)) substrate. The activity towards N-linolenoylsphingosine (C(18:3)/C(18:1)), N-linoleoylsphingosine (C(18:2)/C(18:1)) and N-oleoylsphingosine (C(18:1)/C(18:1)) were respectively about 5, 4 and 3 times higher than the activity towards N-stearoylsphingosine (C(18:0)/C(18:1)). The activity towards N-stearoyldihydrosphingosine (C(18:0)/C(18:0)) was about 40% of that towards N-stearoylsphingosine. Fibroblast alkaline ceramidase possessed significant activity only towards ceramides of unsaturated fatty acids, with a pH optimum of about 9.0. Deficiency of acid ceramidase activity in fibroblasts from patients with Farber disease and intermediate activities in obligate heterozygotes were demonstrated with all ceramides examined except for N-hexanoylsphingosine (C(6:0)/C(18:1)), whereas alkaline ceramidase activity was unaffected. Comparative kinetic studies of acid ceramidase activity with N-lauroylsphingosine and N-oleoylsphingosine demonstrated about 5 (2-12)-fold and 7 (4-17)-fold higher K(m) values in fibroblasts from patients with Farber disease as compared with normal controls. N-Lauroylsphingosine, towards which acid ceramidase activity in control fibroblasts was about 10 times higher than that towards N-oleoylsphingosine, may serve as a better substrate for enzymic diagnosis of Farber disease as well as for further characterization of the catalytically defective acid ceramidase.

Catalytically defective ganglioside neuraminidase in mucolipidosis IV

Cultured skin fibroblasts from patients with mucolipidosis IV were found to be deficient in neuraminidase activity toward GD1a and GD1b gangliosides radiolabelled in C8 and C7 analogs of their sialic acid residues. Neuraminidase activities toward 4-methylumbelliferyl-N-acetyl-neuraminic acid, neuraminlactose, and radiolabelled neuraminlactitol, fetuin and alpha 1-acid glycoprotein were within the range of normal controls. Fibroblasts from parents of patients with mucolipidosis IV demonstrated intermediate levels of ganglioside neuraminidase activity and normal levels of glycoprotein neuraminidase activity. The residual acidic neuraminidase activity toward GD1a ganglioside in the patients' fibroblasts did not differ from that of controls in its pH optimum and thermostability, but had an abnormal apparent Km which was about 18 times higher than that of the normal enzyme. These findings suggest that mucolipidosis IV is a ganglioside sialidosis due to a catalytically defective ganglioside neuraminidase.

Apparently normal extracellular acidic alpha-mannosidase in fibroblast cultures from patients with mannosidosis

Fibroblasts from patients with mannosidosis, cultured in medium supplemented with fetal calf serum from which acidic alpha-mannosidase (alpha-D-mannoside mannohydrolase, E.C.3.2.1.24) has been removed, secreted a normal amount of apparently unaffected acidic alpha-mannosidase into fetal calf serum-free medium. Both the intracellular and extracellular acidic alpha-mannosidase activities were completely precipitated by antiserum to placenta alpha-mannosidase B. In contrast to the heat-lability of the intracellular acidic alpha-mannosidase and its low affinity for artificial mannoside substrate, the extracellular enzyme exhibited both normal thermostability and normal kinetics. Mixing experiments with the intercellular enzymes suggested that the decreased activity in the patients' fibroblasts is not the effect of an inhibitor or absence of an activator. However, incubation of the mannosidosis extracellular enzyme with either normal or patient cell lysate resulted in a partial loss of activity, whereas an additive value was observed with the normal extracellular enzyme. In contrast to normal culture medium, the medium from mannosidosis cell culture was unable to enhance the rate of reduction of intracellular radioactivity in mucolipidosis type II fibroblasts precultured in the presence of radiolabeled mannose. These findings suggest that the defect in mannosidosis is expressed only after the enzyme has been delivered to lysosomes and presumably undergone some form of processing there.

The metabolism of sialic acid in cystic fibrosis

The activities of plasma and fibroblast cytidine 5'-monophosphate-sialic acid:glycoprotein sialyltransferases of patients with cystic fibrosis have been found to be within the range of activities of age- and sex-matched normal controls when asialofetuin served as the sialic acid acceptor. The use of desialylated preparations of purified human plasma alpha 2-macroglobulin, as an acceptor, demonstrated 35 to 52% reduction in the incorporation of sialic acid into the alpha 2-macroglobulin from patients with cystic fibrosis as compared to that of alpha 2-macroglobulin from normal controls. The reduced sialylation was dependent upon the source of the alpha 2-macroglobulin acceptor but independent of the source (cystic fibrosis or normal) of the sialyltransferase enzyme. Using radiolabeled precursors, the rates of the synthesis of N-acetylneuraminic acid from N-acetyl-D-mannosamine, the release of sialic acid from glycoproteins and the conversion of free sialic acid into CMP-sialic acid have been determined in cultured skin fibroblasts from patients with cystic fibrosis and found to be not significantly different from those of normal controls.

Deficient phosphorylation of mannose residues of mannan in fibroblasts of patients with mucolipidoses II and III

Incorporation of 32P from [gamma 32P]ATP into mannan could not be detected in homogenates of cultivated skin fibroblasts from patients with mucolipidosis II, and accounted for only up to 10% of normal control activity in cell lysates from patients with mucolipidosis III. Parents of patients with mucolipidosis II demonstrated 60-70% of normal control activity. On high-voltage electrophoresis, the hydrolysed mannan from reactions performed with normal cells, over the pH range 5.5-7.5, yielded a radioactive band migrating with the same mobility as mannose 6-phosphate, whereas no such product could be demonstrated in fibroblasts of patients with mucolipidosis II.

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.

Normal two-dimensional gel electrophoresis of alpha-2-macroglobulin in cystic fibrosis

Some studies have suggested that a mutant form of alpha-2-macroglobulin (alpha-2-M) could be the primary defect in cystic fibrosis (CF). To test for the presence of charge change amino acid substitutions, alpha-2-M was examined by two-dimensional gel electrophoresis following complete denaturation of the proteins. The pattern of nine charge isomers observed was the same in homozygous, heterozygous, and normal individuals.

Decreased sialic acid and altered binding to lectins of purified alpha 2-macroglobulin from patients with cystic fibrosis

Purified preparations of plasma alpha 2-macroglobulin from patients with cystic fibrosis are shown to have normal amounts of total hexose but as much as 40% decrease in their sialic acid content. The binding of these preparations to concanavalin A and wheat-germ agglutinin was markedly reduced as compared to normal values in controls. Intermediate values were found in obligate heterozygotes. These results suggest a possible alteration in the carbohydrate moiety of alpha 2-macroglobulin in cystic fibrosis, presumably due to a defective posttranslational process.

Demonstration of altered acidic hydrolases in fibroblasts from patients with mucolipidosis II by lectin titration

Decreased binding by the lectins concanavalin A and wheat-germ agglutinin was found for a number of acidic hydrolases from skin fibroblasts of three unrelated patients with mucolipidosis II. This decreased binding as compared with normal controls was demonstrated by titration of hydrolase activities with increasing amounts of immobilized lectins. Neuraminidase treatment slightly improved the binding of enzymes from mucolipidosis-II patients, in contrast with the diminished binding found or hydrolases from control cell lines. The abnormality in binding by lectins of hydrolases of mucolipidosis-II patients was observed for enzymes with various degrees of intracellular deficiency as well as for enzymes with normal intracellular activities. These findings suggest a generalized alteration of fibroblast acidic hydrolase molecules in mucolipidosis II.

Multiple carbohydrate-cleaving specificities in human acidic and neutral glycosidases

The common identity of human acidic beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) and beta-D-xylosidase (1,4-beta-D-xylan xylohydrolase, EC 3.2.1.37) as one enzyme and that of acidic beta-D-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23), beta-D-fucosidase (no allotted EC number) and alpha-L-arabinosidase (alpha-L-arabinofuranoside arabinohydrolase, EC 3.2.1.55) as another enzyme is indicated by similar binding patterns of glycosidase activities of each enzyme to various lectins. by similar ratios between their intra- and extracellular levels in normal and I-cell fibroblasts and by their deficiencies in liver tissues from patients with Gaucher disease and GM1 gangliosidosis, respectively. A third enzyme, neutral beta-D-galactosidase, purified to homogeneity from human liver has been shown to possess all these five glycosidase activities at neutral pH. These neutral enzymic activities were not bound by any of the lectins examined and found to be reduced in liver and spleen of a patient with neutral beta-D-galactosidase deficiency. An additional form of beta-D-xylosidase with optimal activity at pH 7.4 was bound by the fucose-binding lectin from Ulex eurpaeus while no binding was observed for the acidic (pH 4.8) and neutral (pH 7.0) beta-D-xylosidase activities of the multiple glycosidase enzymes.

Binding of human liver hydrolases by immobilized lectins

The binding of 22 human liver hydrolase activities by immobilized lectins of six different carbohydrate specificities, namely alpha-D-mannose (glucose), D-N-acetylglucosamine, D-N-acetylgalactosamine, L-fucose, alpha-D-galactose and beta-D-galactose, were examined. Differences in binding among these enzymes and within specific enzymes were observed. For example, the neutral forms of alpha-mannosidase and beta-xylosidase were bound by the Ulex europaeus lectin I (specific for L-fucose), whereas the acidic forms were not. Bandierea simplicifolia lectin (specific for alpha-galactose) bound 65% of beta-glucuronidase activity; recycling experiments demonstrated complete binding of the enzyme that had been eluted with the competitor D-galactose and no binding of the fraction that was not initially bound. These results suggested the presence of two forms of this enzyme. Similar data were obtained for acidic beta-galactosidase activity. These experiments may provide the basis for the expanded use of immobilized lectins for purification and characterization of hydrolases and other glycoproteins.

The nature of mutation in Krabbe disease

Galactosylceramide beta-galactosidase cross reacting material was demonstrated in brain, liver, and skin fibroblasts from patients with Krabbe disease. The mutant enzyme was antigenically identical to the normal enzyme and exhibited similar electrophoretic mobility. Normal quantities of the catalytically deficient enzyme were measured in the patients' tissues by a sensitive single radial immunodiffusion assay, indicating that the mutation is in structural gene for the enzyme protein.

Pitfalls in the use of artificial substrates for the diagnosis of Gaucher's disease

A patient with Gaucher's disease is described, in whom the disease could not be diagnosed enzymically in liver and leucocytes using artificial substrate 4-methylumbelliferyl beta-glucoside. Normal activity was found in the liver, and about 60% of control activity was determined in the patient's leucocytes. In contrast, when [14C]-N-stearoyl glucocerebroside was employed as a substrate, activity as low as 5% of control has been found in all the proband's tissues, and carrier levels were determined in the proband's parents and maternal uncle.

Lactosyl ceramidosis: deficient activity of neutral beta-galactosidase in liver and cultivated fibroblasts?

Neutral beta-galactosidase was partially purified from liver of normal controls, a patient with Niemann-Pick disease type A and the previously described patient with lactosyl ceramidosis using Concanavalin A-Sepharose adsorption and Sephadex G-100 gel filtration. The partially purified fractions were essentially free of galactosyl ceramide beta-galactosidase and GM1 beta-galactosidase activities. The normal and Niemann-Pick fractions were found to hydrolyze lactosyl ceramide, in the presence of sodium taurodeoxycholate, at a pH optimum of 5.6 as well as aryl beta-galactosides and aryl beta-glucosides at pH 6.2. The corresponding fraction from the lactosyl ceramidosis liver contained only 1--4% of the normal activity towards artificial substrates and lactosyl ceramide. Cross-reacting material identical to the normal was demonstrated in this fraction with antiserum raised against purified neutral beta-galactosidase, but no activity was observed in the precipitin line when stained with naphthol AS-LC-beta-galactoside or naphthol AS-LC-beta-glucoside. A similar deficiency of neutral beta-galactosidase activity was demonstrated in cultivated fibroblasts of the patient with lactosyl ceramidosis. Following adsorption on Concanavalin A-Sepharose and anti-GM1 beta-galactosidase antibody-Sepharose conjugates and chromatography on DEAE cellulose, fibroblast lysates from the patient exhibited 3% of normal activity towards 4-methyl-umbelliferyl beta-glucoside at pH 6.2 and 12% of normal activity towards lactosyl ceramide at pH 5.6. These data suggest that neutral beta-galactosidase may have an in vivo role in the cleavage of lactosyl ceramide and that a deficiency of this activity may be related to the lactosyl ceramide accumulation observed in the patient with lactosyl ceramidosis.

Quantitation of the enzymically deficient cross reacting material in GM1 gangliosidoses

Normal quantities of GM1 beta-galactosidase cross reacting material (CRM) (0.31-0.47 microgram/mg protein) were detected by a sensitive radial immunodiffusion assay in skin fibroblasts from patients with GM1 gangliosidosis type 1 and adult variants, whereas elevated levels were found in GM1 gangliosidosis type 2 (0.41-0.72 microgram/mg protein). The specific activity of the immunologically CRM towards GM1 ganglioside of normal fibroblasts was about 500 times that of type 1, 100 times that of type 2, and 30 times that of the adult variants.

Abnormal breakdown of alpha2-macroglobulin-trypsin complex in cystic fibrosis

The complex of trypsin with purified alpha2-macroglobulin from normals and patients with cystic fibrosis was studied. The formed complex failed to reveal any proteolytic activity toward a high molecular weight substrate whereas the esterolytic activity towards a low molecular weight substrate was retained. This esterolytic activity was resistant to inhibition by a high molecular weight inhibitor. During iincubation at 38 degrees C the complex with normal alpha2-macroglobulin was slowly inhibited by the high molecular weight inhibitor and regained activity with the high molecular weight substrate. This phenomenon was not obtained when the alpha2-macroglobulin from cystic fibrosis was examined. These data suggest that the gradual conversion of normal alpha2-macroglobulin-trypsin complex into an alpha2-macroglobulin fragment-trypsin complex is deficient in patients with cystic fibrosis.

Immunological evidence for substrate-induced conformational alterations in human carbonic anhydrase B

The inhibition by specific antibody of carbonic anhydrase B activity towards bicarbonate was uncompetitive (Ki 9.5 X 10(-7) M) whereas that of activity towards p-nitrophenylacetate was mixed-type (Ki 9.2 X 10(-7) M). Differences in the immunological reactivity of the enzyme in the presence of the substrates was documented by quantitative precipitin tests and by the Farr technique. In the presence of bicarbonate, nearly half of the antigenic determinants of the enzyme were altered to such an extent that antibodies directed against these determinants in the native form did not bind. This antibody fraction was separated and shown to react with the native enzyme in different molar ratios than the total antibody population. It produced only a very limited inhibition of the activity towards CO2 and p-nitrophenyl acetate. The immunological reactivity of the enzyme with both the total antibody population and the fraction that is nonreactive in the presence of bicarbonate was identical in the absence of substrates and in the presence of CO2 and p-nitrophenyl acetate. It is suggested that the native enzyme form exhibits enzymatic activity towards CO2 and p-nitrophenyl acetate, whereas in the presence of bicarbonate a "conformational adaptation" is induced.

Specific determination of N-acetyl-beta-D-hexosaminidase isozymes A and B by radioimmunoassay and radial immunodiffusion

The two major isozymes of N-acetylhexosaminidase, namely hexosaminidases A and B were quantitatively determined in tissues and biological fluids of both normal individuals and Tay-Sachs patients. The determination was carried out by two sensitive immunoassays:radial immunodiffusion, using chromogenic substrate, and radioimmunoassay, which were developed in this study. For this purpose [corrected] we used either a cross-reactive antiserum which reacts to a similar extent with both isozymes, or an antiserum reacting exclusively with hexosaminidase A (obtained by selective immunoadsorption). This enabled the quantitisation of the two isozymes separately, or in the presence of each other, in purified enzyme preparations or in tissue homogenates, affording a direct positive determination of hexosaminidase A. The results demonstrated that normal tissues contain the two isozymes in comparable amounts, whereas tissues of Tay-Sachs patients lack hexosaminidase A or any material which carries the A-specific antigenic determinants. The possible applications of these assays and their potential use in diagnosis are discussed.