Biochemical and fine structural studies on brain and liver biopsies in aspartylglucosaminuria

Quantitative determination of rare mRNA species by PCR and solid-phase minisequencing

We present a new method for quantification of mRNA, in which the limitations of the current quantitative PCR methods can be overcome. A known amount of a synthetic RNA standard differing from the mRNA to be quantified by a single nucleotide is reverse-transcribed and amplified together with the mRNA template using a biotinylated primer. The biotinylated PCR product is immobilized on a streptavidin-coated solid support and denatured. The ratio between the two amplified sequences is determined by separate "mini-sequencing" reactions, in which a detection step primer annealing immediately adjacent to the site of the variable nucleotide is elongated by a single labeled dNTP complementary to the nucleotide at the variable site. The ratio between the incorporated labels accurately determines the ratio between the two sequences in the original RNA sample. We applied this method to quantify the mRNA of human aspartylglucosaminidase (AGA) in tissues and cultured cells. AGA is a lysosomal enzyme participating in the degradation of glycoproteins. A mutation in the AGA gene abolishes the enzyme activity and leads to aspartylglucosaminuria (AGU), a recessively inherited metabolic disorder. The mRNA quantification revealed that the normal and mutant genes are expressed at similar levels in kidney, liver, and cultured fibroblast, whereas the amount of AGA mRNA in normal placenta and brain is significantly higher than that found in the corresponding samples from AGU patients. The method presented here is generally applicable for PCR-based quantification of rare mRNAs and DNA as well.

Two Japanese cases with aspartylglycosaminuria: clinical and morphological features

Two members of a consanguineous Japanese family with a clinical picture of aspartylglycosaminuria (AGU) are described. Both patients exhibited mental retardation, coarse facial features, angiokeratoma and myoclonic seizures. Biochemical studies showed elevated excretion of urinary sialyloligosaccharides and decreased activity of aspartylglycosaminidase in lymphoblasts. Morphologic studies of skin biopsy specimens showed many clear vacuoles mainly in the vascular endothelial cells and secretory cells of the sweat glands. Osmiophilic lamellar cytoplasmic inclusions were also noted in the ganglion cells in rectal biopsy. The ethnic distribution of AGU may be more widespread than previously suspected and appears not to be restricted to Finnish populations. Ours are the first Japanese patients diagnosed as AGU. We conclude that AGU should also be included in the differential diagnosis of mentally retarded patients in Asian countries.

Isolation of a human hepatic 60 kDa aspartylglucosaminidase consisting of three non-identical polypeptides

We have characterized the properties of human aspartylglucosaminidase (EC 3.5.1.26), the lysosomal enzyme which is deficient in the human inherited disease aspartylglucosaminuria. The purification procedure from human liver included affinity chromatography, gel filtration, strong-anion- and strong-cation-exchange h.p.l.c., chromatofocusing and reverse-phase h.p.l.c. In a denaturing SDS/polyacrylamide-gel electrophoresis, the 6600-fold purified enzyme was shown to be composed of three non-identical inactive polypeptide chains of molecular masses 24, 18 and 17 kDa. In a native polyacrylamide-gel electrophoresis, these polypeptide chains ran as one active enzyme complex. As judged from the elution position of the native enzyme in a Biogel P-100 gel filtration, the approximate molecular mass of this complex was 60 kDa. The enzyme had a pI of 5.7, a pH optimum at 6, of 0.48 mM and a specific activity of 200,000 nkat for the substrate 2-acetamido-1-beta-(L-aspartamido)-1,2-dideoxy-D-glucose. The enzyme showed a 57% loss of activity at 60 degrees C after 45 h but was practically inactive after incubation at 72 degrees C for a few minutes. The molecular structure, Km and specific activity as well as the thermostability of the enzyme described here are different from those reported previously for human aspartylglucosaminidase.

Measurement of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase activity in human tissues

The activity of 1-aspartamido-beta-N-acetylglucosamine amidohydrolase (aspartylglucosylaminase, EC 3.5.1.26) was measured in normal and diseased human liver, brain and kidney. Organs from patients with aspartylglucosaminuria show very little activity. Crude homogenates of human organs show a reaction catalysed by a complex enzyme system. With homogenate, the formation of product was linear with time up to about 6 h. Reaction times longer than 6-7h resulted in a decrease in the total concentration of product. This phenomenon was not found with the partially purified enzyme fraction. Linearity of the enzyme activity with different protein concentrations was found, independent of the incubation time. Longer incubation of the crude homogenate resulted in the utilization of the product, N-acetylglucosamine. This phenomenon was not observed with the partially purified enzyme fraction. This amidase from human organs differs from that obtained from other sources and apparently represents a rather complex enzyme system.

Inherited metabolic diseases of the nervous system

This overview was designed primarily to provide examples of hereditary metabolic disorders that result in nervous system dysfunction. Some of the more frequently encountered pathological conditions were selected in order to illustrate the mechanisms and the consequences of the metabolic derangements. Therapeutic approaches for the correction of such disorders are discussed where it appears appropriate. In time the precise etiology for those eponymous genetic conditions with stereotyped pathologic and clinical manifestations such as Huntington's chorea (79) and Friedreich's ataxia (80) will be disclosed. It is possible that some forms of epilepsy (81) and perhaps certain psychiatric disturbances (82) will be shown to be inherited metabolic disorders. As our knowledge and skill increase, this logic may eventually be extended to biochemical explanations of variation in individual skills and talents. Certainly innovative extrapolation and novel research directions will be necessary to provide an understanding of these differences. However, it is axiomatic in research that each useful contribution serves largely as a point of departure for further accomplishments.

Aspartylglucosaminuria: unique biochemical and ultrastructural characteristics

The observation of vacuolated lymphocytes in a coarsely featured two year old female with hepatosplenomegaly, mitral insufficiency, and mild psychomotor retardation led to the first diagnosed case of aspartylglucosaminuria in the United States. Although physical characteristics and bone roentgenograms were consistent with a mucopolysaccharide disorder, analysis of the urine showed no mucopolysaccharide elevation. The chromatographic, enzymatic, and ultrastructural studies confirming the diagnosis are presented.

Glycosidases of molluscs. Purification and properties of alpha-L-fucosidase from Chamelea gallina L

An alpha-L-fucosidase had been purified approximately 300-fold from the liver (hepatopancreas) of the marine mollusc Chamelea gallina L. (= Venus gallina L.). During the different steps of the purification procedure it was difficult to remove the contaminant N-acetylglucosaminidase activity; but, after electrofocusing, a final preparation free of this and other glycosidades present in the crude extract was obtained. The purified enzyme has a broad specificity; it hydrolyzes p-nitrophenyl alpha-L-fucoside and natural substrates such as oligosaccharides containing fucosidic residues with alpha 1--2, alpha 1--3 and alpha 1--4 linkages; also it hydrolyzes fucose-containing glycopeptides, such as thyroglobulin glycopeptide, and glycoproteins as procine submaxillary mucin (previously rendered free of sialic acid). The enzyme has a pH optimum of 5.2 +/- 0.2, with a Km of 7 X 10(-5) M using p-nitrophenyl L-fucoside as substrate. It is inhibited by Hg2+ and some sugars, and activated by CN-, Zn2+, Ca2+ and EDTA. It shows two peaks by isoelectric focusing (at 6.3 and 6.6). The molecular weight of the alpha-L-fucosidase by gel filtration was over 2000000.

Aspartylglycosaminuria: a generalized storage disease. Morphological and histochemical studies

Aspartylglycosaminuria (AGU) is a hereditary metabolic disorder characterized by slowly progressive mental deterioration from infancy, urinary excretion of large amounts of aspartylglycosamine, and decreased activity of the lysosomal enzyme aspartylglcosamine amido hydrolase in various body tissues and fluids. The nature and distribution of the morphological and histochemical alterations in AUG are described in the light of the first AGU patient investigated post mortem and brain and liver. Most nerve cells and hepatocytes contained large vacuoles without any histochemically demonstrable lipid or carbohydrate material. Ultrastructural studies revealed numerous electron-lucent vaculoles, limited by a single, membrane, in the cytoplasm of these cells. In addition to evenly disperesed finely granular or reticular material the vacuoles contained small electron-opaque "lipid" droplets and polymorphic membraneous or granular aggregates. Similar vacuoles were also seen in a number of other cell types, particularly in the kupffer cells and brain macrophages, as well as in the capillary pericytes. Biochemical studies suggest that the principal storage material consists of aspartylglycosamine itself; glycoasparagines of higher molecular weight are present as only minor components. Correlated morphological and biochemical studies thus definitely establish that AGU is a generalized storage disorder. The condition is apparently due to decreased activity of aspartylglycosamine amido hydrolase, with accumulation of products of flycoprotein carabolism in cytoplasmic vacuoles in both epithelial and mesenchymal cells.

The glycoasparagines in urine of a patient with aspartylglycosaminuria

The isolation and analysis of 2-acetamido-N-(4'-l-aspartyl)-2-deoxy-beta-d- glucopyranosylamine and 13 higher-molecular-weight derivatives from the urine of a patient with aspartylglycosaminuria is described. Some structural information is presented for nine of these compounds.