Mannosidosis: detection of the disease and of heterozygotes using serum and leucocytes

Alpha-mannosidosis: correlation between phenotype, genotype and mutant MAN2B1 subcellular localisation

Background

Alpha-mannosidosis is caused by mutations in MAN2B1, leading to loss of lysosomal alpha-mannosidase activity. Symptoms include intellectual disabilities, hearing impairment, motor function disturbances, facial coarsening and musculoskeletal abnormalities.

Methods

To study the genotype-phenotype relationship for alpha-mannosidosis 66 patients were included. Based on the predicted effect of the mutations and the subcellular localisation of mutant MAN2B1 in cultured cells, the patients were divided into three subgroups.

Clinical and biochemical data were collected. Correlation analyses between each of the three subgroups of genotype/subcellular localisation and the clinical and biochemical data were done to investigate the potential relationship between genotype and phenotype in alpha-mannosidosis.

Statistical analyses were performed using the SPSS software. Analyses of covariance were performed to describe the genotype-phenotype correlations. The phenotype parameters were modelled by the mutation group and age as a covariate. P values of <0.05 were considered as statistically significant.

Results

Complete MAN2B1 genotypes were established for all patients. We found significantly higher scores in the Leiter-R test, lower concentrations of CSF-oligosaccharides, higher point scores in the Bruininks-Oseretsky Test of Motor Proficiency subtests (BOT-2); Upper limb coordination and Balance, and a higher FVC% in patients in subgroup 3, harbouring at least one variant that allows localisation of the mutant MAN2B1 protein to the lysosomes compared to subgrou 2 and/or subgroup 1 with no lysosomal localization of the mutant MAN2B1 protein.

Conclusion

Our results indicate a correlation between the MAN2B1 genotypes and the cognitive function, upper limb coordination, balance, FVC% and the storage of oligosaccharides in CSF. This correlation depends on the subcellular localisation of the mutant MAN2B1 protein.

Lysosomal enzyme activities in skeletal muscle of patients with neuromuscular diseases

Activities of nine lysosomal enzymes and pH-dependent isozyme patterns of alpha-mannosidase were examined in the skeletal muscle of patients with neuromuscular diseases, and the ratios of these enzyme activities in leukocytes to those in myocytes (L/M ratio) were determined. The activities of enzymes with a high L/M ratio were markedly increased in the muscles of patients with Duchenne muscular dystrophy (DMD), myotonic dystrophy (MyD), or polymyositis (PM). In contrast, those which showed a low L/M ratio were increased in the muscles of amyotrophic lateral sclerosis (ALS) and disuse muscle atrophy (DUA). The isozyme pattern of alpha-mannosidase in DMD muscle resembled that in leukocytes, while those in ALS and DUA muscle resembled that in normal muscle. These results may suggest that the increased activity of lysosomal enzymes in the muscles of patients with DMD, MyD, or PM is due primarily to infiltrating leukocytes, while that in patients with ALS or DUA is due to intramyofiber lysosomes.

Serum alpha-mannosidase activity and the clinicopathologic alterations of locoweed (Astragalus mollissimus) intoxication in range cattle

Subclinical intoxication of livestock with Astragalus and Oxytropis species (locoweeds) results in decreased animal feed conversion, reduced weight gains, and reproductive failure. Sensitive diagnostic methods to definitively diagnose and monitor intoxication are needed to minimize these losses and better manage locoweed-infested pastures and rangelands. Sera from cattle grazing locoweed were evaluated for alpha-mannosidase activity, serum biochemical values, electrolytes, and thyroid hormone concentrations. As the cows began to ingest locoweed, the mean serum alpha-mannosidase activities dropped significantly (400.0 microM to 72.5 microM). Changes in other serum chemistry values were less specific; however, individual animals (generally those ingesting more locoweed) had elevated levels of alkaline phosphatase (ALP), aspartate aminotransferase, and lactate dehydrogenase, with decreased serum total protein (5.8 +/- 0.8 g/dl) and albumin (2.3 +/- 0.3 g/dl). Mean serum thyroid concentrations (both T4 and T3) were lower in animals that were ingesting locoweed. The calculated swainsonine dose correlated statistically with serum alpha-mannosidase activity, ALP, albumin, Cl, CO2, and thyroid hormone T3. This correlation suggests that serum alpha-mannosidase activity along with potential changes in ALP, albumin, and thyroid hormone concentrations is a sensitive indicator of locoweed exposure and intoxication. These parameters may also be useful for monitoring intoxication and allowing subclinically affected cattle to be removed from infested areas before irreversible damage occurs.

alpha-D-mannosidase forms in chicken liver

Two forms (I and II) of alpha-D-mannosidase have been separated by ion-exchange chromatography on DEAE-cellulose from embryonic chicken liver. A third form (III), which is absent in embryos, was also separated from 4-day-old chickens. The optimum pH of form I is at pH 5.0. Form II is named "neutral" because it shows maximal activity at pH 6.5. The optimum pH of form III is 4.5. Forms I and III are heat-stable at 50 degrees C for 1 hr, whereas form II is very unstable under these conditions. Zn2+ and Mg2+ have been found to increase the alpha-D-mannosidase activity of forms I and II. In contrast, Co2+ increases mannosidase I activity and inhibits form II from 18-day-old embryos. alpha-Methyl-D-mannoside, N-acetyl-D-mannosamine and D-mannosamine were found to be inhibitors of both forms I and II. "Neutral" mannosidase was also inhibited by chloride. Competitive inhibition by D-mannose was also studied and Ki values are given.

alpha-D-mannosidases in serum of patients with I-cell disease (ICD)

The specific activity of alpha-D-mannosidase in serum of ICD-patients is considerably increased due to increased amounts of the component with optimal activity at pH 4.6 (acidic form). The intermediate form with pH optimum of 6.0 remains unaltered. These conclusions were reached by using optimal conditions for differential assay of the alpha-D-mannosidases checked by partial separation of the components in serum by sucrose gradient centrifugation.

Unusual clinical and ultrastructural features in a boy with biochemically typical mannosidosis

A 4 1/2-year-old boy with a history of recurring respiratory tract infections and seizures, and evidence of severe retardation of psychomotor development and growth, lacked the coarse facial features, skeletal changes and other clinical stigmata generally associated with mannosidosis, but the total alpha-mannosidase activity in his leukocytes, cultured fibroblasts and liver were no more than 10% of the control mean. Studies of the residual alpha-mannosidase enzyme suggest a specific deficiency of the thermostable isoenzyme with an acidic pH optimum. The alpha-mannosidase in the fibroblasts of our and another (control) patient with mannosidosis had a reduced affinity for the substrate 4-methylumbelliferyl-alpha-D-mannoside. Light microscopy of the liver biopsy showed an increase in connective tissue often distorting the hepatic architecture; numerous tiny vacuoles, small dense and lipid bodies in most hepatocytes, and similar but more extensive changes in sinusoidal cells; and sinusoidal pools of hepatocytic debris. Electron microscopy of hepatocytes revealed vacuoles similar but not identical to those described in reported mannosidosis patients, and in addition several forms of secondary lysosomes; prominent peroxisomes (microbodies); increased numbers of profiles of smooth endoplasmic reticulum; dilated rough endoplasmic reticulum containing traces of fine granulo-fibrillar material; increased numbers of rosettes of alpha particles of glycogen and reduced numbers of mitochondria with alterations in their distribution, size and configuration. It is believed that the usual clinical and hepatic ultrastructural features in our patient reflect another variant of mannosidosis.

Biochemical studies on a case of feline mannosidosis

Evidence is presented for the biochemical diagnosis of the first case of feline mannosidosis. A marked deficiency of acidic alpha-D-mannosidase in the brain, kidney and liver and excessive excretion of mannose-rich oligosaccharides in the urine were found in a kitten suffering from a nervous disorder. Residual acidic alpha-D-mannosidase, ranging from 2 to 5.5% of the normal activity, was observed in the tissues of the affected kitten. It has similar kinetic and physicochemical properties to the normal activity. The amount of mannose in the urine of the affected kitten was 19-fold greater than in a comparable control, and the molar ratio of mannose to N-acetylglucosamine was approx. 6 : 1. High concentrations of neutral oligosaccharides were detected in the urine. The predominant oligosaccharide appeared to be a hexasaccharide. The biochemical features of bovine, feline and human mannosidosis are compared, and it is concluded that feline mannosidosis may be a useful animal model for studying the human disease.

Plasma acid hydrolases in normal adults and children, and in patients with some lysosomal storage diseases

Optimal assay conditions are described for plasma alpha-galactosidase, beta-glactosidase, beta-glucuronidase, alpha-mannosidase, alpha-glucosidase, N-acetyl-beta-glucosaminidase, alpha-fucosidase, N-acetyl-alpha-glucosaminidase, acid phosphatase and arylsulphatase A. The levels of these activities in normal adults and children, and the stabilities of the activities on storage at -20 degrees C or 4 degrees C, are reported. The levels of these enzymic activities in plasma from patients with Fabry, Pompe, Sanfilippo A, Sanfilippo B, Tay Sachs and Hunter diseases, GM1-gangliosidosis and metachromatic leucodystrophy are described, and the possibility of using plasma hydrolase activities in the diagnosis of these conditions is discussed.

Lysosomal glycosidase activities in human hair roots

The levels of three lysosomal glycosidase, alpha-D-mannosidase, a-L-fucosidase and beta-D-hexosaminidase have been determined in normal hair roots and in hair roots obtained from a patient with mannosidosis. The most active glycosidase in normal hair roots was beta-D-hexosaminidase, followed by alpha-L-fucosidase and alpha-D-mannosidase. There was no alpha-D-mannosidase activity in the hair roots of the patient with mannosidosis. The significance of these results is discussed in relation to the detection of lysosomal storage diseases.

Histomorphologic and histochemical investigations in mannosidosis. A light and electron microscopic study

Morphologic and histochemical studies have been performed at light and electron microscopic level on needle-liver biopsy specimens, circulating blood lymphocytes and fibroblast cultures from patients with mannosidosis. The findings demonstrated generalized storage phenomena of varying degrees in the various tissues examined. Histochemical findings were in agreement with the biochemical nature of the stored material. Enzyme histochemical methods indicated storage in the lysosomes, at least in the hepatocytes. The ultrastructural appearance of mannosidosis in itself has but a limited diagnostic significance since the morphology and distribution of vacuoles have characteristics in common with other storage diseases. Repeated liver biopsy disclosed extensive storage in the hepatic tissue. However, the progression of the disease was not accompanied by severe mechanical destruction or microcirculatory disturbances.

Measurement of the alpha-mannosidase activities in human plasma by a differential assay

A differential assay based on their difference in thermal stability has been used to measure the acidic and true intermediate alpha-mannosidases in the plasma of cntrols and individuals homozygous or heterozygous for mannosidosis. The intermediate activity was found to be independent of age, sex or mannosidosis genotype. The acidic alpha-mannosidase did not vary significantly with age or between sexes for groups of the same age. The concentrations of acidic and intermediate alpha-mannosidase showed a positive correlation for adults but not for children. The ratio of acidic to true intermediate alpha-mannosidase might therefore be a useful secondary test for the detection of adult heterozygotes for mannosidosis.

Mannosidosis. Clinical and biochemical study

The clinical, radiological, and biochemical features of 2 male children with mannosidosis are described. Superficially they appeared to suffer from Hurler's syndrome, but the facies, eye signs, radiological and cytological features were atypical. Excess urinary oligosaccharides were found by thin-layer chromatography. The diagnosis was confirmed by determining the acidic alpha-mannosidase activity of leucocytes and cultured skin fibroblasts. Prenatal diagnosis is possible from cultured amniotic cells.

A gene apparently determining the extent of sialylation of lysosomal alpha-mannosidase in mouse liver

Organ-specific electrophoretic heterogeneity of lysosomal alpha-mannosidase has been observed within individual strains of inbred mice. Polymorphism between C57BL/6J and CBA/J for liver lysosomal alpha-mannosidase is determined by a single genetic locus on chromosome 5 and appears to be the result of differences in sialylation of the lysosomal enzyme. Two different patterns of expression of development of the liver electrophoretic forms have been observed.

Clinical manifestations of mannosidosis--a longitudinal study

Mannosidosis is a partially defined disorder of glycoprotein metabolism; less than 20 cases have been reported in the literature. In this work, a longitudinal study of five new patients is presented in an attempt to delineate the phenotype and clinical course of this unusual storage disease. The data on our patients and those in the literature indicate that people with mannosidosis appear normal at birth and that their typical phenotype develops by two years of age. This is characterized by a distinctive coarse facies and dysostosis multiplex. Although recurrent infections, hearing loss and mental retardation occur, the course in this storage disorder generally is stable and is compatible with adult life. The diagnosis is confirmed by the presence of a deficiency in alpha-D-mannosidase activity in leukocytes or fibroblasts, by the presence of vacuolated lymphocytes in peripheral blood and foam cells in bone marrow, and an increased excretion of mannose-rich oligosaccharides in urine.

Neutral alpha-mannosidase activity in human serum

Two types of alpha-mannosidase (alpha-D-mannoside mannohydrolase, EC 3.2.1.24) with neutral pH optima exist in serum. The activity with an optimum between pH 6.0 and 6.4 is similar to alpha-mannosidase C, described earlier in tissues. The second activity, with a pH optimum between pH 5.2 and 5.8 is the dominant form in serum. These two forms can be differentiated from each other by gel-filtration, chromatography on DEAE-cellulose or chromatography on Concanavalin-A Sepharose. Using the chromatographic techniques, the serum type neutral activity co-elutes with the acidic forms of the enzyme. However, these two forms can be easily distinguished by effect of pH, heating or inhibition by the substrate methyl-alpha-D-mannopyranoside. The presence of the serum type alpha-mannosidase activity is discussed with respect to mannosidosis, a lysosomal storage disease.

Mannosidosis: deficiency of a specific alpha-mannosidase component in cultured fibroblasts

Evidence is prisented which shows that the enzymatic defect in mannosidosis, the deficiency of alpha-mannosidase, is expressed in cultured skin fibroblasts from patients with mannosidosis. Additionally, by Cellogel electrophoresis, the enzyme can be separated into two major components (a heat stable component missing in mannosidosis fibroblasts with a pH optimum of 3.6-4.0 and a heat labile component present in mannosidosis fibroblasts with a pH optimum of 5.6-6.0). The specific activity and electrophoresis of alpha-mannosidase from cultured amniotic fluid cells are also shown to be similar to cultured skin fibroblasts.