GLYCOGEN STORAGE DISEASE

Variable X-chromosome inactivation and enlargement of pericentral glutamine synthetase zones in the liver of heterozygous females with OTC deficiency

Ornithine transcarbamylase (OTC) deficiency is an X-linked disorder that causes recurrent and life-threatening episodes of hyperammonemia. The clinical picture in heterozygous females is highly diverse and derives from the genotype and the degree of inactivation of the mutated X chromosome in hepatocytes. Here, we describe molecular genetic, biochemical, and histopathological findings in the livers explanted from two female patients with late-onset OTC deficiency. Analysis of X-inactivation ratios by DNA methylation-based assays showed remarkable intra-organ variation ranging from 46:54 to 82:18 (average 70:30, n = 37), in favor of the active X chromosome carrying the mutation c.583G>C (p.G195R), in the first patient and from 75:25 to 90:10 (average 82:18, n = 20) in favor of the active X chromosome carrying the splicing mutation c.663+1G>A in the second patient. The X-inactivation ratios in liver samples correlated highly with the proportions of OTC-positive hepatocytes calculated from high-resolution image analyses of the immunohistochemically detected OTC in frozen sections that was performed on total area > 5 cm². X-inactivation ratios in blood in both female patients corresponded to the lower limit of the liver values. Our data indicate that the proportion of about 20-30% of hepatocytes expressing the functional OTC protein is not sufficient to maintain metabolic stability. X-inactivation ratios assessed in liver biopsies taken from heterozygous females with X-linked disorders should not be considered representative of the whole liver.

Effect of administration of the fructose on the glycogenolytic action of glucagon. An investigation of the pathogeny of hereditary fructose intolerance

1. The mechanism by which the administration of fructose to patients with hereditary fructose intolerance makes them unresponsive to the hyperglycaemic action of glucagon was studied. In four patients, a 10-fold increase in the urinary excretion of cyclic AMP was induced by glucagon, but this effect was drastically decreased by the previous administration of fructose (250mg/kg). Further, the intravenous injection of 6-N,2'-O-dibutyryl cyclic AMP did not cause an increase in the blood glucose during fructose-induced hypoglycaemia. 2. The administration of a large dose of fructose (5g/kg) to mice decreased markedly both the concentration of ATP and the increase in the concentration of cyclic AMP caused by glucagon in the liver. Other ATP-depleting agents had a similar effect and a linear correlation could be drawn between the concentration of ATP and the change in cyclic AMP concentration; a half-maximal effect was obtained for a concentration of ATP close to the K(m) value of adenylate cyclase. 3. The administration of fructose to mice caused the inactivation of phosphorylase in the liver, but this effect was easily reversed by glucagon. 4. At a concentration of 10mm-fructose 1-phosphate and 1.5mm-P(i), purified liver phosphorylase a was inhibited by 70%. This inhibition appears to be a likely explanation for the unresponsiveness to glucagon of patients with hereditary fructose intolerance.

Characterization of hepatic and brain metabolism in young adults with glycogen storage disease type 1: a magnetic resonance spectroscopy study

In glycogen storage disease type 1 (GSD1), children present with severe hypoglycemia, whereas the propensity for hypoglycemia may decrease with age in these patients. It was the aim of this study to elucidate the mechanisms for milder hypoglycemia symptoms in young adult GSD1 patients. Four patients with GSD1 [body mass index (BMI) 23.2 +/- 6.3 kg/m, age 21.3 +/- 2.9 yr] and four healthy controls matched for BMI (23.1 +/- 3.0 kg/m) and age (24.0 +/- 3.1 yr) were studied. Combined (1)H/(31)P nuclear magnetic resonance spectroscopy (NMRS) was used to assess brain metabolism. Before and after administration of 1 mg glucagon, endogenous glucose production (EGP) was measured with d-[6,6-(2)H(2)]glucose and hepatic glucose metabolism was examined by (1)H/(13)C/(31)P NMRS. At baseline, GSD1 patients exhibited significantly lower rates of EGP (0.53 +/- 0.04 vs. 1.74 +/- 0.03 mg.kg(-1).min(-1); P < 0.01) but an increased intrahepatic glycogen (502 +/- 89 vs. 236 +/- 11 mmol/l; P = 0.05) and lipid content (16.3 +/- 1.1 vs. 1.4 +/- 0.4%; P < 0.001). After glucagon challenge, EGP did not change in GSD1 patients (0.53 +/- 0.04 vs. 0.59 +/- 0.24 mg.kg(-1).min(-1); P = not significant) but increased in healthy controls (1.74 +/- 0.03 vs. 3.95 +/- 1.34; P < 0.0001). In GSD1 patients, we found an exaggerated increase of intrahepatic phosphomonoesters (0.23 +/- 0.08 vs. 0.86 +/- 0.19 arbitrary units; P < 0.001), whereas inorganic phosphate decreased (0.36 +/- 0.08 vs. -0.43 +/- 0.17 arbitrary units; P < 0.01). Intracerebral ratios of glucose and lactate to creatine were higher in GSD1 patients (P < 0.05 vs. control). Therefore, hepatic defects of glucose metabolism persist in young adult GSD1 patients. Upregulation of the glucose and lactate transport at the blood-brain barrier could be responsible for the amelioration of hypoglycemic symptoms.

Elevated serum biotinidase activity in hepatic glycogen storage disorders--a convenient biomarker

An elevated serum biotinidase activity in patients with glycogen storage disease (GSD) type Ia has been reported previously. The aim of this work was to investigate the specificity of the phenomenon and thus we expanded the study to other types of hepatic GSDs. Serum biotinidase activity was measured in a total of 68 GSD patients and was compared with that of healthy controls (8.7 +/- 1.0; range 7.0-10.6 mU/ml; n = 26). We found an increased biotinidase activity in patients with GSD Ia (17.7 +/- 3.9; range: 11.4-24.8; n = 21), GSD I non-a (20.9 +/- 5.6; range 14.6-26.0; n = 4), GSD III (12.5 +/- 3.6; range 7.8-19.1; n = 13), GSD VI (15.4 +/- 2.0; range 14.1-17.7; n = 3) and GSD IX (14.0 +/- 3.8; range: 7.5-21.6; n = 22). The sensitivity of this test was 100% for patients with GSD Ia, GSD I non-a and GSD VI, 62% for GSD III, and 77% for GSD IX, indicating reduced sensitivity for GSD III and GSD IX, respectively. In addition, we found elevated biotinidase activity in all sera from 5 patients with Fanconi-Bickel Syndrome (15.3 +/- 3.7; range 11.0-19.4). Taken together, we propose serum biotinidase as a diagnostic biomarker for hepatic glycogen storage disorders.

Restoration of the glycogen-forming function of hepatocytes in rats with liver cirrhosis is facilitated by a high-carbohydrate diet

Using cytofluorimetric and biochemical methods, the content of glycogen and its labile and stable fractions, as well as activities of glucose-6-phosphatase (EC 3.1.3.9), glycogen phosphorylase (EC 2.4.1.1) and glycogen synthase (EC 2.4.1.11) were determined in the rat liver for 6 months after chronic poisoning of the animals with CCl4 and then at 1, 3, and 6 months after the end of the poisoning. One group of rats was given a standard diet, the other, a high-carbohydrate diet. The 6-month long chronic intoxication with CCl4 was shown to produce development of typical liver cirrhosis characterized by a 2·8-fold increase in the total glycogen content in hepatocytes as compared with normal cells, by a fall in the glycogen labile fraction (from 85 to 53 % of the total glycogen) as well as by decreases in the activities of glycogen phosphorylase and glucose-6-phosphatase by 25 and 82% respectively. The structural rehabilitation occurred faster and more completely at the cellular level than at the tissue level. Functional variables of the cirrhotic liver tissue also recovered, after cessation of poisoning, faster and more completely than the liver structure at the tissue level: glycogen levels in hepatocytes fell dramatically, the labile: stable glycogen fraction ratio recovered completely, and the activity of glycogen phosphorylase rose to the level characteristic of the normal liver. Use of the high-carbohydrate diet promoted a somewhat faster and more complete recovery of hepatic structure and function.

Familial X-linked cardiomyopathy (Danon disease): diagnostic confirmation by mutation analysis of the LAMP2gene

A boy presented at age 2.5 years with mild left ventricular hypertrophy and mild myopathy. Hypertrophic cardiomyopathy progressed relentlessly, leading to death at age 16 years shortly before planned heart transplantation. During the course of the disease, his mother developed severe dilated cardiomyopathy and died of its complications at 46 years of age. The combination of myopathy and cardiomyopathy, the biochemical and electron microscopy findings in a muscle biopsy, and the pedigree suggested Danon disease (MIM 300257), an X-linked lysosomal storage disorder caused by deficiency of lysosome-associated membrane protein-2 (LAMP2). The diagnosis was confirmed by the identification of a novel mutation, G138A, in the LAMP2gene, leading to the premature stop codon W46X.

CONCLUSION

Early diagnosis of Danon disease is important for genetic counselling and timely cardiac transplantation, the only effective therapeutic option.

Glycogen-forming function of hepatocytes in cirrhotically altered rat liver after treatment with chorionic gonadotropin

Using cytofluorimetric and biochemical studies on serial supravital liver punctate biopsies, effects of chorionic gonadotropin (CG) on recovery of hepatocyte glycogen-forming function in the cirrhotically altered rat liver were analyzed. The biopsies were taken first from rats with experimental cirrhosis produced by their 6-month-long poisoning with the hepatotoxic poison CCl4, then from the same animals in 1, 3, and 6 month after cessation of their poisoning, either on treatment with CG or with no treatment. In smears of isolated hepatocytes, the contents of the total glycogen (TG) and of its labile and stable fractions (LF and SF, respectively) were measured. In liver homogenates, activities of glucose-6-phosphatase (G6Pase), glycogen phosphorylase, and glycogen synthetase were determined. It was found that the threefold increased TG content in hepatocytes of cirrhotic liver returned to the normal level in 3 months without treatment, while as soon as in 1 month in the case of the treatment with CG. The CG treatment for 3 months resulted in normalization of the glycogen fraction composition that had been changed in cirrhotic liver, whereas without treatment, the glycogen LF/SF ratio remained changed even after 6 months after cessation of the poisoning with CCl4. Activity of G6Pase was fourfold reduced in cirrhosis; in 3 months after the end of poisoning, under effect of CG, the activity increased to the normal level, but somewhat decreased subsequently. In the animals that were not treated with CG, the decrease in the G6Pase activity after the cessation of the CCl4 poisoning was even more marked than in the CG-treated rats. Activities of two other enzymes of glycogen metabolism did not differ statistically significantly from the norm throughout the entire experiment. The data obtained indicate that the use of CG for rehabilitation of the glycogen-forming function of the cirrhotically altered liver is more efficient than other ways of treatment studied previously, such as partial hepatectomy or a high-carbohydrate diet.

Ontogeny of the murine glucose-6-phosphatase system

A deficiency in microsomal glucose-6-phosphatase (G6Pase) activity causes glycogen storage disease type 1 (GSD-1), a clinically and biochemically heterogeneous group of diseases. It has been suggested that catalysis by G6Pase involves multiple components, with defects in the G6Pase catalytic unit causing GSD-1a and defects in the putative substrate and product translocases causing GSD-1b, 1c, and 1d. However, this model is open to debate. To elucidate the G6Pase system, we have examined G6Pase mRNA expression, G6Pase activity, and glucose 6-phosphate (G6P) transport activity in the murine liver and kidney during normal development. In the liver, G6Pase mRNA and enzymatic activity were detected at 18 days gestation and increased markedly at parturition, before leveling off to adult levels. In the kidney, G6Pase mRNA and enzymatic activity appeared at 19 days gestation and peaked at weaning, suggesting that kidney G6Pase may have a different metabolic role. In situ hybridization analysis demonstrated that, in addition to the liver and kidney, the intestine expressed G6Pase. Despite the expression of G6Pase in the embryonic liver, microsomal G6P transport activity was not detectable until birth, peaking at about age 4 weeks. Our study strongly supports the multicomponent model for the G6Pase system.

Asparagine-linked oligosaccharides are localized to a luminal hydrophilic loop in human glucose-6-phosphatase

Deficiency of glucose-6-phosphatase (G6Pase), an endoplasmic reticulum transmembrane glycoprotein, causes glycogen storage disease type 1a. We have recently shown that human G6Pase contains an odd number of transmembrane segments, supporting a nine-transmembrane helical model for this enzyme. Sequence analysis predicts the presence of three potential asparagine (N)-linked glycosylation sites, N96TS, N203AS, and N276SS, conserved among mammalian G6Pases. According to this model, Asn96, located in a 37-residue luminal loop, is a potential acceptor for oligosaccharides, whereas Asn203 and Asn276, located in a 12-residue cytoplasmic loop and helix 7, respectively, would not be utilized for this purpose. We therefore characterized mutant G6Pases lacking one, two, or all three potential N-linked glycosylation sites. Western blot and in vitro translation studies showed that G6Pase is glycosylated only at Asn96, further validating the nine-transmembrane topology model. Substituting Asn96 with an Ala (N96A) moderately reduced enzymatic activity and had no effect on G6Pase synthesis or degradation, suggesting that oligosaccharide chains do not play a major role in protecting the enzyme from proteolytic degradation. In contrast, mutation of Asn276 to an Ala (N276A) destabilized the enzyme and markedly reduced enzymatic activity. We present additional evidence suggesting that the integrity of transmembrane helices is essential for G6Pase stability and catalytic activity.

Transmembrane topology of glucose-6-phosphatase

Deficiency of microsomal glucose-6-phosphatase (G6Pase), the key enzyme in glucose homeostasis, causes glycogen storage disease type 1a, an autosomal recessive disorder. Characterization of the transmembrane topology of G6Pase should facilitate the identification of amino acid residues contributing to the active site and broaden our understanding of the effects of mutations that cause glycogen storage disease type 1a. Using N- and C-terminal tagged G6Pase, we show that in intact microsomes, the N terminus is resistant to protease digestion, whereas the C terminus is sensitive to such treatment. Our results demonstrate that G6Pase possesses an odd number of transmembrane helices, with its N and C termini facing the endoplasmic reticulum lumen and the cytoplasm, respectively. During catalysis, a phosphoryl-enzyme intermediate is formed, and the phosphoryl acceptor in G6Pase is a His residue. Sequence alignment suggests that mammalian G6Pases, lipid phosphatases, acid phosphatases, and a vanadium-containing chloroperoxidase (whose tertiary structure is known) share a conserved phosphatase motif. Active-site alignment of the vanadium-containing chloroperoxidase and G6Pases predicts that Arg-83, His-119, and His-176 in G6Pase contribute to the active site and that His-176 is the residue that covalently binds the phosphoryl moiety during catalysis. This alignment also predicts that Arg-83, His-119, and His-176 reside on the same side of the endoplasmic reticulum membrane, which is supported by the recently predicted nine-transmembrane helical model for G6Pase. We have previously shown that Arg-83 is involved in positioning the phosphate during catalysis and that His-119 is essential for G6Pase activity. Here we demonstrate that substitution of His-176 with structurally similar or dissimilar amino acids inactivates the enzyme, suggesting that His-176 could be the phosphoryl acceptor in G6Pase during catalysis.

Hepatoprotective effects of Eclipta alba on subcellular levels in rats

The hepatoprotective effect of the ethanol/water (1:1) extract of Eclipta alba (Ea) has been studied at subcellular levels in rats against CCl4-induced hepatotoxicity. Ea significantly counteracted CCl4-induced inhibition of the hepatic microsomal drug metabolising enzyme amidopyrine N-demethylase and membrane bound glucose 6-phosphatase, but failed to reverse the very high degree of inhibition of another drug metabolising enzyme aniline hydroxylase. The loss of hepatic lysosomal acid phosphatase and alkaline phosphatase by CCl4 was significantly restored by Ea. Its effect on mitochondrial succinate dehydrogenase and adenosine 5'-triphosphatase was not significant. The study shows that hepatoprotective activity of Ea is by regulating the levels of hepatic microsomal drug metabolising enzymes.

Mutations in the glucose-6-phosphatase gene that cause glycogen storage disease type 1a

Glycogen storage disease (GSD) type 1a is caused by the deficiency of D-glucose-6-phosphatase (G6Pase), the key enzyme in glucose homeostasis. Despite both a high incidence and morbidity, the molecular mechanisms underlying this deficiency have eluded characterization. In the present study, the molecular and biochemical characterization of the human G6Pase complementary DNA, its gene, and the expressed protein, which is indistinguishable from human microsomal G6Pase, are reported. Several mutations in the G6Pase gene of affected individuals that completely inactivate the enzyme have been identified. These results establish the molecular basis of this disease and open the way for future gene therapy.

Conversion of fructose to glucose in the rabbit small intestine. A reappraisal of the direct pathway

Gopher et al [Gopher, A., Vaisman, N., Mandel, H. & Lapidot, A. (1990) Proc. Natl Acad. Sci. USA 87, 5449-5453] recently reported that about 50% of the glucose formed from [U-13C]fructose infused nasogastrically in children contained 13C3 adjacent to 13C4. Assuming a high isotopic dilution of the triosephosphate pool, the authors concluded that about 50% of the fructose converted to glucose in liver and intestine bypassed the classical aldolase pathway, utilizing a hypothetical direct pathway that would involve the phosphorylation of fructose 1-phosphate to fructose 1,6-bisphosphate. The present work was undertaken in order to establish to what extent the conversion of fructose to glucose in the intestine could account for this unexpected isotopic distribution. The technique of everted sleeves was used to define the rate of conversion of [U-14C]glucose and [U-14C]fructose in the small intestine of 24-h-fasted rabbits. It appeared that, at the low concentration of fructose used by Gopher et al., almost as much fructose was converted to glucose as remained unmodified in the tissue. Fructose uptake was not inhibited by glucose, and the presence of all the necessary enzymes in the tissue indicated that the fructose to glucose conversion occurred by the aldolase pathway. Remarkably, this conversion operated with an isotopic dilution not exceeding 25%, due to the low rate of glucose metabolism and the near absence of gluconeogenesis from lactate. It can, therefore, be postulated that, in the presence of pure [U13C]fructose, the triosephosphate pool is highly enriched in 13C with little dilution by 12C, essentially giving rise to [U-13C]glucose, as reported by Gopher et al. There is, therefore, no need to postulate the participation of a direct pathway.

Impairment of the activity of the hepatic microsomal glucose-6-phosphatase system in three preterm infants

Three preterm infants born at 26-30 weeks' gestation who died between 103 and 266 days after birth were found to have elevated hepatic glycogen levels. Kinetic analysis of the hepatic microsomal glucose-6-phosphatase system demonstrated that one infant had abnormally low levels of activity of the glucose-6-phosphatase enzyme (partial type 1a glycogen storage disease) and two had deficiencies of T2, a microsomal phosphate/pyrophosphate transport protein (type 1c glycogen storage disease). In all three cases glycogen storage disease was not suspected prior to death even though both hypo- and hyperglycaemic episodes were recorded in the first 15 days after birth indicating that they had somewhat disordered blood glucose regulation. In the infant with low glucose-6-phosphatase enzyme activity, abnormal development of the glucose-6-phosphatase enzyme cannot be ruled out. This is the first description of abnormalities in the glucose-6-phosphatase system in preterm infants.

Heat-stable protein that stimulates acid alpha-glucosidase

A hot-water extract of bovine spleen and guinea pig liver exhibited the ability to enhance acid alpha-glucosidase activity, with methylumbelliferyl alpha-glucoside, glycogen or maltose as substrate. The level of activator required for maximal stabilization was similar for all three substrates, indicating direct action on the enzyme rather than on substrate. The stimulator was partially purified by chromatography with gel-permeation (apparent Mr 20,000-24,000), ion-exchange and C4 reverse-phase columns. It was retained by a narrow-pore dialysis tubing and destroyed by treatment with Pronase, and is presumably a protein. The stimulating protein protected the enzyme against denaturation by heat or incubation with a buffer of high ionic strength in the absence of substrate. RNA inhibited the enzyme, and the activator protein was able to counteract the effect. Activating material was found in a variety of mouse and rat tissues, as well as human urine.

Use of platelets, mononuclear and polymorphonuclear cells in the diagnosis of glycogen storage disease type VI

We determined glycogen concentration and phosphorylase 'a+b' and phosphorylase a activities in platelets, mononuclear and polymorphonuclear cells from control subjects and patients with phosphorylase kinase deficiency (glycogen storage disease IX) and liver phosphorylase deficiency (glycogen storage disease VI). Variations according to cellular type and to subjects' age (1-40 years) were established. Variable glycogen overloading was found in all our patients. Glycogen storage disease (GSD) VI was characterized by a diminished total phosphorylase activity with a low or normal a/(a+b) ratio of phosphorylase activity. GSD IX was characterized by a very low residual activity of phosphorylase a with an 'a+b' activity low or normal.

Diagnosis of type 1a and type 1c glycogen storage diseases in adults

The hepatic glucose-6-phosphatase system was studied with a novel microanalytical technique in adult patients undergoing liver biopsy. 4 patients were diagnosed as having type 1 glycogen storage disease (GSD). 3 of these patients, who had hypoglycaemic symptoms, had variations of type 1a GSD, which is caused by a defect in the hepatic microsomal glucose-6-phosphatase enzyme. The fourth, with hepatomegaly and no hypoglycaemic symptoms, had a normal glucose-6-phosphatase enzyme but a defect in the hepatic microsomal phosphate/pyrophosphate translocase T2; this is the first report of an adult with type 1c GSD. Adult type 1 GSD should be considered in patients with unresolved hypoglycaemic symptoms and/or unresolved hepatomegaly.

Liver-specific glucose-6-phosphatase is not present in human placenta

Type I glycogen storage disease (McKusick 23220), an inherited absence or deficiency of glucose-6-phosphatase (EC 3.1.3.9) activity in the liver, kidney and intestine, is associated with the accumulation of glycogen in those organs. Previous reports have shown that glucose-6-phosphatase exists in human placenta and that detection of a heterozygote for this disorder from placenta might be possible. Our finding of a normal glucose-6-phosphatase activity in a placenta from a patient at risk for type Ia glycogen storage disease prompted us to examine in more detail placental glucose-6-phosphatase. Unexpectedly, we found the properties of the placental enzyme differed from that in normal liver, and the placental enzyme hydrolyzed glucose-6-phosphate, mannose-6-phosphate, beta-glycerol phosphate and glucose-1-phosphate equally well. Our data suggest the enzyme deficient in type I glycogen storage disease cannot be detected in placenta.

[Diagnostic significance of muscle biopsies in metabolic myopathies. II. Clinical biochemistry]

In the diagnosis of metabolic myopathies the use of biochemical methods, in addition to morphological examination of muscle biopsies, is often necessary in order to identify a specific metabolic defect. In order to narrow down the spectrum of biochemical methods, extensive clinical investigation and morphological examination, including histology, enzyme histochemistry and electromicroscopy if necessary have to be done beforehand. Patients are classified in the following groups: 1) progressive muscular weakness and/or muscle wasting with storage of a) glycogen, b) lipid or c) mitochondrial alterations; 2) recurrent rhabdomyolysis induced by fasting or exercise a) with glycogen storage or b) without any specific morphological alterations. The spectrum of metabolic defects comprises disorders of glycogen and glucose metabolism (deficiency of acid maltase, debranching and branching enzyme, phosphorylase, phosphofructokinase and other glycolytic enzymes), lipid metabolism (carnitine deficiency, carnitine palmitoyl transferase deficiency), mitochondria (respiratory chain disorders, pyruvate dehydrogenase deficiency) and others such as adenylate deaminase deficiency. In some of these e.g. infantile acid maltase deficiency and mitochondriopathies, it is clinically more important when organs other than muscle are affected; however, muscle biopsy is a useful substrate for diagnosis of these metabolic disorders.

[Diagnostic significance of muscle biopsies in metabolic myopathies. I. Myopathology]

The clinical course of metabolic myopathies is dominated by progressive muscle weakness and wasting or aching contraction and recurrent rhabdomyolysis with intense exercise. Vacuolar muscle fibre degeneration is the leading pathological finding on routine histological examination. For further characterization of those histologically empty looking vacuoles, histochemistry and electron microscopy are employed. Increase of glycogen, lipid droplets or mitochondria can often be demonstrated and indicate the need for subsequent biochemical identification of the underlying metabolic defect. Some other metabolic myopathies that cause recurrent rhabdomyolysis lack myopathological abnormalities. These can only be diagnosed biochemically, but additional new histochemical screening methods might be helpful.

Cloning a cDNA for the lysosomal alpha-glucosidase

Messenger RNA was isolated from monkey testes and size-fractionated on sucrose gradients. In vitro translation of these mRNA fractions resulted in nascent, labeled alpha-glucosidase that could be precipitated with anti human alpha-glucosidase antiserum. A cDNA library was constructed from the most enriched fraction. The library was screened with cDNA made from mRNA obtained from immunoselected polysomes. Five cross-hybridizing clones were isolated and identified by their selection of alpha-glucosidase mRNA, as shown by hybrid released translation and further by their ability to hybridize with DNA from human chromosome 17, on which the gene coding for acid alpha-glucosidase is located.

Zonal differences of alpha-glucosidases in human kidney: studies in controls and in patients with glycogenosis type II

In the kidneys of two infants who died from glycogenosis type II (deficiency of lysosomal acid alpha-glucosidase) the activity of alpha-glucosidase at acid pH was absent only from the medulla but not the cortex. This prompted an investigation of acid and neutral alpha-glucosidases of the two zones of normal human kidney and of liver. In the kidney medulla, a single, fast migrating electrophoretic band was active at neutral but not at acid pH. In the cortex, three additional bands were detected at neutral pH and two in the liver. One slowly migrating band was unique to the cortex and active over a broad pH range. It had comparatively high sensitivity to the inhibitor turanose and high heat stability. Its properties suggested a close relationship or identity to glucoamylase of the intestinal brush border membrane and to alpha-glucosidase in leukocytes and amniotic fluid and cells.

Glucose-6-phosphatase as a marker for tumors of liver and kidney origin

Glucose-6-phosphatase is primarily a liver and kidney enzyme. This enzyme was studied in various tumors, however, glucose-6-phosphatase activity was found only in tumors of liver, kidney, or adrenal origin. Glucose-6-phosphatase activity was useful in identifying the tissue origin of extrarenal Wilms'. Metastatic tumors within the liver or kidney that originated from other tissues did not have glucose-6-phosphatase activity. Therefore, it is suggested that glucose-6-phosphatase can be used as a specific enzyme marker for tumors of liver and kidney origin.

[Morphological and biochemical studies on glycogenosis type V (McArdle) (author's transl)]

This report deals with structural and biochemical studies of muscle biopsies from six patients with glycogenosis type V (McArdle). From a morphological point of view in four cases the typical findings of vacuolar myopathy with glycogen storage especially under the sarcolemma can be demonstrated. One biopsy shows only mild structural changes which without additional biochemical analysis could be overlooked. In one case signs of recovery phase after rhabdomyolysis predominate the storage myopathy. Biochemical studies in all cases show an elevated glycogen content (2.5-4.23%). Only the from a clinical point of view most expressive patient with recurrent episodes of rhabdomyolysis exhibits a glycogen storage over 5%. All cases additionally show an absence or highly reduction of phosphorylase activity. Apart from the most expressive clinical course the extent of morphological and biochemical findings is not clearly correlated. Therefore if clinical signs suggest the diagnosis of glycogenosis type V it appears necessary to perform additional biochemical examination of muscle biopsy independent from the degree of morphological anomalies.

Endogenous glucose production in Type I glycogen storage disease

The adaptive mechanisms that protect some patients with Type I glycogen storage disease from fasting hypoglycemia were examined in two young adults. Both maintained low normal fasting plasma glucose concentrations even during 3 day fasts; blood lactate concentrations increased during the first 12 hr and then decreased to normal during the second and third days. Acute hyperglycemic responses to glucagon nearly doubled after three days of starvation when compared with responses following 12 hr fasts. Enhanced glucagon-induced hyperglycemic changes also were observed following the administration of alcohol or glucocorticoids. However, fructose infusions failed to demonstrate hyperglycemic responses after a 3 day fast, alcohol or glucocorticoids. The present studies demonstrate endogenous glucose production in our patients despite an absence of the enzyme glucose-6-phosphatase. These findings could explain why some patients with Type I glycogen storage disease are protected from fasting hypoglycemia.

Recurrent hypoglycemia associated with glutaric aciduria type II in an adult

Repeated episodes of hypoglycemia accompanied by elevated serum concentrations of free fatty acid without ketosis, fatty infiltration of the liver, hepatic dysfunction, and proximal myopathy in a 19-year-old woman, prompted us to analyze her urine for organic acids. Greatly increased quantities of glutaric acid, ethylmalonic acid, dicarboxylic acids with six to 10 carbons, and isovalerylglycine were consistently found in her urine. The ability of cultured skin fibroblasts from the patient to oxidize [1(-14)C]butyrate and [2(-14)C]lysine was reduced. These urinary and in vitro findings indicated defective activity of several acyl coenzyme A dehydrogenases, including glutaryl, isovaleryl, and butyryl coenzyme A dehydrogenases -- establishing a diagnosis of glutaric aciduria Type II. Carnitine concentrations in the skeletal muscle and liver were moderately reduced, but carnitine deficiency was considered a secondary biochemical abnormality. Although glutaric aciduria Type II has previously been described only in a neonate, the disease must be considered in the differential diagnosis of hypoglycemia in adults.

Development of gluconeogenic enzymes in fetal sheep liver and kidney

In the sheep, the system of enzymes necessary for conversion of nonhexose substrates to glucose becomes active during late fetal life. Glucose-6-phosphatase and fructose-1,6-diphosphatase, two of the four key gluconeogenic enzymes, appear in significant amounts between 100 and 120 days gestation. Phosphoenolpyruvate carboxykinase activity is comparable to mature animals as early as 45 days gestation. Two aminotransferases, necessary to allow amino acid access to the gluconeogenic pathway, likewise have substantial activity as early as 45 days gestation. Hence, the surge of glucose-6-phosphatase and fructose-1,6-diphosphatase at 100-120 days gestation makes possible the endogenous production of new glucose by fetal sheep at a time when the amount of glucose transferred from the maternal circulation is less than the total aerobic substrate utilized by the fetus. Both renal cortex and liver have similar developmental patterns for the gluconeogenic enzymes, although renal cortex generally shows greater activity than liver. This observation holds true for tissue from both fetal and mature animals.

Type IV glycogenosis - a study of two cases

Liver biopsy materials of two siblings with type IV glycogenosis were studied by light and electron microscopy. Biochemical analysis was added using autopsy material in one of the two cases. Two kinds of polysaccharides were noted not only in the cardiac muscle, skeletal muscles, smooth muscles and reticuloendothelial cells, but also in the neutrophils and platelets. One was glycogen and the other was similar to amylopectin. Ultrastructurally, a large amount of fibrils, 60 A in width, glycogen rosettes and glycogen granules were detected in those cells. Branching glycosyltransferase deficiency was biochemically confirmed in one case examined.

Ketosis in hepatic glycogenosis

The occurrence of ketosis in 41 patients with liver glycogenosis and a control group of 22 children was investigated. Fasting ketosis was present in children with a deficiency of the debranching enzyme system and in young children with a deficiency of the phosphorylase system, but never in patients with a glucose-6-phosphatase deficiency. Oral tolerance tests on a patient deficient in debranching enzyme showed that the blood levels of glucose and ketone bodies changed in the opposite direction. It is argued that, for biochemical reasons, the occurrence of ketosis in patients with a glucose-6-phosphatase deficiency is improbable.