Diagnosis of the mucopolysaccharidoses using cultured skin fibroblasts and amniotic fluid cells

Assay of alpha-L-iduronidase, heparin sulphamidase, N-acetyl-alpha-D-glucosaminidase, arylsulphatase B, alpha-L-fucosidase, beta-glucuronidase, beta-galactosidase and alpha-D-mannosidase in cultured cells is described. Activities in deficient fibroblast strains are compared to control fibroblast strains. The first case of Sanfilippo B in the United Kingdom is reported. A comparison of enzyme activities in cultured fibroblasts and amniotic fluid cells is made.

Alpha-L-fucosidase in cultured bone marrow fibroblasts from fucosidosis patients

Bone marrow fibroblasts were cultured from two patients with fucosidosis type 2, six control subjects, and three patients with other lysosomal disorders. Optimal conditions for measuring alpha-L-fucosidase activity in lysates of these cells with the fluorogenic substrate 4-methylumbelliferyl-alpha-L-fucoside were established. The pH profile of normal bone marrow fibroblasts showed three peaks and a shoulder of enzymatic activity, with maximum activity at pH 4.75. In cells derived from fucosidosis patients two peaks of apparent alpha-L-fucosidase activity were obtained; the pH optimum was 4.5. alpha-L-Fucosidase activity (mean +/- SD) in the fucosidosis and control bone marrow fibroblasts was 2.5 and 312.4 +/- 10.9 nmoles 4-methylumbelliferone per milligram protein per hour, respectively. A reduction in the apparent specific enzymatic activity in the fucosidosis cells was observed by using increasing concentrations of cellular protein in the assay system. Mixing experiments between normal and fucosidosis cells gave the expected activities. These findings indicate that cultured bone marrow fibroblasts can be used for the diagnosis and study of fucosidosis.

Lysosomal (leucocyte) proteinase and sulfatase levels in Dyggve-Melchior-Clausen (DMC) syndrome

Patients with the DMC syndrome have been suggested to possess a specific sulfatase abnormality and/or to be deficient in a proteinase cleaving glycoprotein-acid mucopolysaccharide (AMP) linkage. We have previously found in DMC patients an abnormal excretion of urinary AMPs of which hyaluronic acid and chondroitin sulfate (A + C) were oversulfated and keratosulfate and heparan sulfate were undersulfated. Lysosomal acid proteinase, i.e. cathepsin D (EC 3.4.23.5) and neutral proteinase : elastase (EC 3.4.21.11) and cathepsin G were found to be normal in DMC patients. However, alpha 2-macroglobulin in serum was raised. This increase may be associated with a complex formation of alpha 2-macroglobulin with a neutral proteinase released from the cells. Increased levels of chondroitin sulfate N-acetylgalactosamine-6-sulfate sulfatase and sulfamidase and decreased enzymic levels of arylsulfatase A and B (EC 3.1.6.1) were found in leucocytes of DMC patients. The sulfatase activities assayed in the present study support our theory that a specific sulfatase abnormality may exist in the DMC syndrome.

alpha-L-Iduronidase activity in established lymphoblastoid cells from patients with Hurler and Scheie syndromes transformed by Epstein-Barr virus

alpha-L-Iduronidase activity was determined in established lymphoblastoid cells, which were transformed in vitro by Epstein-Barr virus, of lymphocytes-rich cell populations isolated from peripheral blood of patients with Hurler and Scheie syndromes. alpha-L-Iduronidase activities in established lymphoblastoid cells from patients were undetectable, while activities of control subjects were clearly detected. These results suggest that established lymphoblastoid cells are useful for the enzymatic study of genetic mucopolysaccharidoses.

Genetic heterogeneity within the chondroitinsulphaturias

The approach, identification of clinical phenotype followed by lysosomal enzyme assays in cell culture, used in the classification of the genetic mucopolysaccharidoses I-VI has been applied to the chondroitinsulphaturias. There was evidence of heterogeneity in the first 9 patients reported.

beta-Galactosidase in mucopolysaccharidoses and mucolipidoses. Deficiency of GM1 beta-galactosidase in liver and leukocytes

beta-Galactosidase activities were studied in livers and leukocytes of mucopolysaccharidoses and mucolipidoses (I-cell disease and adult "beta-galactosidase deficiency" with macular cherry-red spots). Marked deficiency of hepatic 4-methylumbelliferyl (4MU) and GM1 beta-galactosidases was demonstrated in these diseases. Leukocyte GM1 beta-galactosidase was also deficient in mucolipidoses. The parents of the patients with I-cell disease and "beta-galactosidase deficiency" had normal beta-galactosidase activity in plasma and leukocytes, compared to the low enzyme activity in heterozygous carriers of GM1-gangliosidosis. The cause of this enzyme deficiency in these diseases is not clear at present. It seems to be affected seondarily by exgenous factors such as unknown stored materials in the cells. Mucopolysaccharides were not increased in the livers of two cases of I-cell disease and a case of "beta-galactosidase deficiency".

Iduronate sulfatase activity in serum, lymphocytes, and fibroblasts--simplified diagnosis of the Hunter syndrome

A previously described assay for iduronate sulfatase has been adapted for use with serum, lymphocytes, and fibroblasts. The assay also gives a rough measure of iduronidase activity. We have evaluated the procedure for the diagnosis of the Hunter syndrome, for the detection of Hunter heterozygotes, and for the diagnosis of certain other disorders (mucolipidoses II and III and mucopolysaccharidosis I). Hunter patients had 1-2% normal iduronate sulfatase activity in the three sources tested. The serum assay is undoubtedly the method of choice to establish the diagnosis of the Hunter syndrome. Less that 1 ml serum and 3-4 days are required to complete the procedure. Serum could not be used for the detection of iduronidase deficiency diseases, but these could easily be recognized in lymphocyte and fibroblast preparations. The iduronate sulfatase activity of sera from patients with mucolipidoses II and III was elevated 20-fold, but their parents had a normal level of the enzyme. In fibroblasts of patients with mucolipidoses II and III, both iduronate sulfatase and iduronidase activities were markedly decreased. Serum assays were not informative about the Hunter heterozygote status. However, the mean activity in lymphocytes from mothers of Hunter patients was about half of the mean normal activity. A number of obligate heterozygotes had iduronate sulfatase activity so low that they were identifiable as carriers; others, unfortunately, had a clearly normal level. The possibility of carrier detection by the lymphocyte assay needs further development.

The mucopolysaccharidoses: inborn errors of glycosaminoglycan catabolism

The mucopolysaccharidoses are genetic disorders of glycosaminoglycan metabolism. Patients with these diseases accumulate within the lysosomes of most tissues excessive amounts of dermatan and/or heparan sulfates, or of keratan sulfate. The clinical consequences of such glycosaminoglycan storage range from skeletal abnormalities to cardiovascular problems, and to motor and mental retardation. In all mucopolysaccharidoses, except Morquio disease, an excessive accumulation of sulfate-labeled glycosaminoglycans has been demonstrated in fibroblasts cultured from the patient's skin. It was subsequently shown that this was due to the deficiency of specific proteins which were named "corrective factors", because their addition to the culture medium effected a normalization of the impaired glycosaminoglycan catabolism in the respective mucopolysaccharidosis fibroblasts. The investigation of the function of the corrective factors, and other studies, led to the identification of the enzymatic defect in each of the mucopolysaccharidoses. Seven lysosomal enzyme deficiencies are now recognized among this group of disorders. A classification of the diseases, according to the mutant gene products, reveals that there is considerable phenotypic variation not only between diseases, but also within several disease types. With the availability of the appropriate enzyme assays, the previous difficulties in diagnosing these disorders have now been overcome. Methods are also available for the prenatal diagnosis, and the detection of heterozygous individuals, in most of the mucopolysaccharidoses. Although correction of the metabolic defect through enzyme replacement has been achieved in tissue culture, many problems remain to be solved before such therapy may become applicable in the patients themselves.

The mucopolysaccharidoses (a review)

The mucopolysaccharidoses are a group of genetic diseases characterized by storage of incompletely degraded glycosaminoglycans. Such storage causes marked distortion of many tissues with consequent severe somatic changes and mental retardation. Storage of glycosaminoglycans results from markedly diminished activity of specific hydrolases requisite for the normal degradation of glycosaminoglycans. The specific enzymic defects have been identified in nine different diseases. In some cases evidence has been obtained indicating the existence of additional allelic diseases based on the same enzyme. The knowledge obtained from these studies has made prenatal diagnosis possible and has led to the possibility that therapy may be undertaken utilizing enzyme replacement.

Sanfilippo disease type B: presence of material cross reacting with antibodies against alpha-N-acetylglucosaminidase

1. alpha-N-Acetylglucosaminidase, the enzyme deficient in Sanfilippo disease type B (mucopolysaccharidosis III B) was purified from normal human urine. An antiserum was raised in rabbits against the purified enzyme. Preincubation of the antiserum with crude alpha-N-acetylglucosaminidase from normal human urine, followed by centrifugation, led to a marked reduction of the enzyme activity in the supernatant. Formation of the antibody-enzyme complex had no influence on the activity. The thermal stability of the enzyme was markedly enhanced by complex formation with the antiserum. 2. In the urine from three patients with Sanfilippo disease type B the presence of cross-reacting material could be demonstrated by incubating the antiserum with alpha-N-acetylglucosaminidase in the presence of Sanfilippo B urine or by pretreatment of the antiserum with Sanfilippo B urine. 3. Immunodiffusion and immunoelectrophoresis of crude normal or Sanfilippo B urine gave rise to up to four precipitation lines, only one of which exhibited alpha-N-acetylglucosaminidase activity in the case of normal urine. Purified alpha-N-acetylglucosaminidase yielded only a single precipitation line. After adsorption with the purified enzyme the antiserum did not cross react with any of the urinary proteins. 4. On a quantitative determination of cross-reacting material using Sepharose immobilized antibodies in the urine from two Sanfilippo B patients the amount of cross-reacting material appeared to be less than one fourth of the amount of alpha-N-acetylglucosaminidase protein in an age-matched control urine. The cross-reacting material present in the urine of Sanfilippo B patients had a significant lower binding affinity for antibodies against alpha-N-acetylglucosaminidase than preparations from normal human urine. Taking into account this lower binding affinity, it can be calculated that the amount of cross-reacting material in the urine of Salfilippo B patients exceeds that of normal controls. 5. It is concluded that Sanfilippo disease type B is due to a mutation of a structural gene coding for alpha-N-acetylglucosaminidase. The mutation affects the catalytical and immunological properties of the enzyme protein.