A Noncoding Variant Near PPP1R3B Promotes Liver Glycogen Storage and MetS, but Protects Against Myocardial Infarction

CONTEXT

Glycogen storage diseases are rare. Increased glycogen in the liver results in increased attenuation.

OBJECTIVE

Investigate the association and function of a noncoding region associated with liver attenuation but not histologic nonalcoholic fatty liver disease.

DESIGN

Genetics of Obesity-associated Liver Disease Consortium.

SETTING

Population-based.

MAIN OUTCOME

Computed tomography measured liver attenuation.

RESULTS

Carriers of rs4841132-A (frequency 2%-19%) do not show increased hepatic steatosis; they have increased liver attenuation indicative of increased glycogen deposition. rs4841132 falls in a noncoding RNA LOC157273 ~190 kb upstream of PPP1R3B. We demonstrate that rs4841132-A increases PPP1R3B through a cis genetic effect. Using CRISPR/Cas9 we engineered a 105-bp deletion including rs4841132-A in human hepatocarcinoma cells that increases PPP1R3B, decreases LOC157273, and increases glycogen perfectly mirroring the human disease. Overexpression of PPP1R3B or knockdown of LOC157273 increased glycogen but did not result in decreased LOC157273 or increased PPP1R3B, respectively, suggesting that the effects may not all occur via affecting RNA levels. Based on electronic health record (EHR) data, rs4841132-A associates with all components of the metabolic syndrome (MetS). However, rs4841132-A associated with decreased low-density lipoprotein (LDL) cholesterol and risk for myocardial infarction (MI). A metabolic signature for rs4841132-A includes increased glycine, lactate, triglycerides, and decreased acetoacetate and beta-hydroxybutyrate.

CONCLUSIONS

These results show that rs4841132-A promotes a hepatic glycogen storage disease by increasing PPP1R3B and decreasing LOC157273. rs4841132-A promotes glycogen accumulation and development of MetS but lowers LDL cholesterol and risk for MI. These results suggest that elevated hepatic glycogen is one cause of MetS that does not invariably promote MI.

Links between autophagy and disorders of glycogen metabolism - Perspectives on pathogenesis and possible treatments

The glycogen storage diseases are a group of inherited metabolic disorders that are characterized by specific enzymatic defects involving the synthesis or degradation of glycogen. Each disorder presents with a set of symptoms that are due to the underlying enzyme deficiency and the particular tissues that are affected. Autophagy is a process by which cells degrade and recycle unneeded or damaged intracellular components such as lipids, glycogen, and damaged mitochondria. Recent studies showed that several of the glycogen storage disorders have abnormal autophagy which can disturb normal cellular metabolism and/or mitochondrial function. Here, we provide a clinical overview of the glycogen storage disorders, a brief description of autophagy, and the known links between specific glycogen storage disorders and autophagy.

Glucose and glycogen in the diabetic kidney: Heroes or villains?

Glucose metabolism in the kidney is currently foremost in the minds of nephrologists, diabetologists and researchers globally, as a result of the outstanding success of SGLT2 inhibitors in reducing renal and cardiovascular disease in individuals with diabetes. However, these exciting data have come with the puzzling but fascinating paradigm that many of the beneficial effects on the kidney and cardiovascular system seem to be independent of the systemic glucose lowering actions of these agents. This manuscript places into context an area of research highly relevant to renal glucose metabolism, that of glycogen accumulation and metabolism in the diabetic kidney. Whether the glycogen that abnormally accumulates is pathological (the villain), is somehow protective (the hero) or is inconsequential (the bystander) is a research question that may provide insight into the link between diabetes and diabetic kidney disease.

Recurrent infantile hypoglycemia due to combined fructose-1,6-diphosphatase deficiency and growth hormone deficiency

A 14-month-old female infant presented with recurrent episodes of acute gastroenteritis accompanied by severe metabolic acidosis and hypoglycemia. Physical examination showed hepatomegaly. Laboratory evaluation revealed elevated hepatic enzymes, prolonged prothrombin time, hyperuricemia, and extremely elevated lactate and alanine levels. Glucagon injection during hypoglycemia resulted in a further decrease of blood glucose. She was treated with glucose-containing intravenous fluids, with rapid improvement and normalization of her blood pH and glucose levels. Hormonal assessment during two episodes of hypoglycemia indicated growth hormone (GH) deficiency. However, as isolated GH deficiency could not explain all other concomitant features, such as severe lactic acidosis, hepatomegaly, impaired liver function, and hyperuricemia, the possibility of a combined defect was suggested. Further lymphocytic enzymatic investigation revealed fructose-1,6-diphosphatase deficiency and molecular genetic analysis demonstrated frame shift mutation in the FBP1 gene. This enzyme deficiency causes a rare metabolic disorder not previously described in combination with GH deficiency.

Clinical resolution of glycogenic hepatopathy following improved glycemic control

Glycogenic hepatopathy is an underrecognized complication of long-standing poorly controlled diabetes mellitus. It is characterized by abnormal glycogen accumulation in hepatocytes, elevated liver enzymes and hepatomegaly. This is a distinct entity from other causes of hepatomegaly and elevated liver enzymes in diabetics such as nonalcoholic fatty liver disease. It is important to distinguish this entity as it has the potential for resolution following improved glycemic control as described by this case report.

A role for AGL ubiquitination in the glycogen storage disorders of Lafora and Cori's disease

Cori's disease is a glycogen storage disorder characterized by a deficiency in the glycogen debranching enzyme, amylo-1,6-glucosidase,4-alpha-glucanotransferase (AGL). Here, we demonstrate that the G1448R genetic variant of AGL is unable to bind to glycogen and displays decreased stability that is rescued by proteasomal inhibition. AGL G1448R is more highly ubiquitinated than its wild-type counterpart and forms aggresomes upon proteasome impairment. Furthermore, the E3 ubiquitin ligase Malin interacts with and promotes the ubiquitination of AGL. Malin is known to be mutated in Lafora disease, an autosomal recessive disorder clinically characterized by the accumulation of polyglucosan bodies resembling poorly branched glycogen. Transfection studies in HepG2 cells demonstrate that AGL is cytoplasmic whereas Malin is predominately nuclear. However, after depletion of glycogen stores for 4 h, approximately 90% of transfected cells exhibit partial nuclear staining for AGL. Furthermore, stimulation of cells with agents that elevate cAMP increases Malin levels and Malin/AGL complex formation. Refeeding mice for 2 h after an overnight fast causes a reduction in hepatic AGL levels by 48%. Taken together, these results indicate that binding to glycogen crucially regulates the stability of AGL and, further, that its ubiquitination may play an important role in the pathophysiology of both Lafora and Cori's disease.

Complete reversal of glycogen hepatopathy with pancreas transplantation: two cases

Glycogen hepatopathy is the pathological overloading of hepatocytes with glycogen that is associated with poorly controlled diabetes mellitus. Clinically, it presents with abdominal discomfort, tender hepatomegaly and elevated transaminases. In this report, we describe our experience with two cases of type I diabetes mellitus and glycogen hepatopathy. The patients underwent isolated pancreas transplantation, following which, we have been able to demonstrate complete histological resolution of glycogen hepatopathy associated with control of glucose metabolism.

Glycogen storage disease

Glycogen storage disease (GSD) is a rare autosomal-recessive disorder characterized by hypoglycemia, hepatosplenomegaly, seizures, and failure to thrive in infants. Neutropenia and/or neutrophil dysfunction develops in GSD1b, but not in other types. GSD1b results from a deficiency of the glucose-6-phosphate translocase enzyme and the genetic defect maps to chromosome 11q23. Patients with GSD1b are susceptible to recurrent bacterial infections, commonly involving the perirectal area, ears, skin, and urinary tract, although life-threatening infections, such as septicemia, pneumonia, and meningitis occur less frequently. Although the exact mechanism of neutropenia in patients with GSD1b is not known, treatment with recombinant human granulocyte colony-stimulating factor (G-CSF) has reduced the incidence of infections and has improved the quality of life of these patients. Defects in neutrophil chemotaxis and intracellular bacterial killing have been described and appear to be corrected by the use of G-CSF. To date, no cases of myelodysplasia or acute myeloid leukemia have been observed in patients with GSD1b treated with G-CSF. A significant complication of cytokine therapy is the development of hypersplenism, requiring either a reduction in the dosage of G-CSF or splenectomy.

[Mitochondrial and metabolic myopathies]

Mitochondrial and metabolic myopathies constitute a group of disorders characterised by abnormal muscular metabolism of energy. Most of these disorders are genetically transmitted. Recent progress in the field has led to spectacular advances in their classification and the understanding of the mechanisms involved, particularly in mitochondrail myopathies. Diagnosis can be made et any age; the patient can present manifestations that can be misleading for the clinician. Lipid myopathies and glycogenoses usually present as a myopathic syndrome associated with cramps, spasm and myalgia, with fatigue on effort. Acute episodes of rhabdomyolysis on effort can occur, with an attendant risk of renal failure. Mitochondrial myopathies have multi-organ manifestations and muscular involvement is not always at the forefront. Although diagnosis may be suggested by clinical factors, it should be confirmed by teams and laboratories that specialize in muscular disorders.

[Secondary glycogenosis (Mauriac's syndrome) in a young man with diabetes mellitus]

A rare observation of secondary glycogenesis in a male of 31 with a long history of irregularly treated diabetes mellitus is described. The diagnosis was established after death and was confirmed histologically, histochemically and electron microscopically.

Diabetes mellitus-associated glycogen storage hepatomegaly: report of a case and review of the Japanese literature

A huge hepatomegaly was seen in a 30-yr-old female diabetic who was treated with high dose of insulin for her uncontrollable food ingestion. The liver function at the peak of the hepatic enlargement showed a moderate increase of transaminases, alkaline phosphatase, and gamma-glutamyl transpeptidase. The histology of the enlarged liver revealed PAS-positive granules in enlarged hepatocytes, indicating the presence of massive glycogen storage. On admission, she was maintained under a calorie-restricted diet and received approximately 15 to 20 units per day of insulin supplement. At one month after admission, a marked shrinkage of her enlarged liver and restoration of normal liver function were observed concomitantly with the return of fair control of her blood sugar levels. One year later, she had an episode of diabetic ketoacidosis which subsequently was treated with a continuous low-dose infusion of insulin; however, she showed neither hepatomegaly nor liver dysfunction during this episode. There have been 20 cases reported of Japanese diabetics with marked hepatomegaly, in whom the vigorous treatment of diabetic ketoacidosis with insulin seemed to be a trigger of the enlarged liver. This has occurred mostly in patients with insulin-dependent diabetes mellitus. We present a case of non-insulin-dependent diabetes mellitus with glycogen storage hepatomegaly, presumably due to excessive insulin supplements. This suggests that glycogen storage hepatomegaly in diabetics may not be only due to an acute restoration from diabetic ketoacidosis, but may also be due to an overinsulinization in an attempt to maintain a euglycemic condition in spite of excess food intake.

Fatal infantile hypertrophic cardiomyopathy secondary to deficiency of heart specific phosphorylase b kinase

We describe here a male infant with a rare form of glycogenosis caused by deficiency of heart specific phosphorylase b kinase. The disease phenotype was characterized by severe glycogenosis restricted to the heart muscle with secondary rapidly progressive hypertrophic cardiomyopathy causing death at the age of 47 days.

[Muscular glycogenoses]

Muscular glycogenosis is a disease resulting from genetic abnormalities altering an enzyme which is involved in glycogen metabolism. In addition to disorders of glycogenolysis and glycolysis, there are other pathological processes such as acid maltase (alpha-glucosidase) deficiency and diseases associated with abnormal glycogen structure. Glycolysis is the only metabolic pathway that can produce ATP in the absence of oxygen. It is then easy to understand that any disturbance in this energy pathway can result in dysfunction of the muscle machine and in a number of symptoms which are common to these abnormalities. An overall review of the various diseases know to exist on the glycogenolytic and glycolytic pathway will enable the reader to acquire a better knowledge of their particular features.

Complex carbohydrates in the dietary management of patients with glycogenosis caused by glucose-6-phosphatase deficiency

Carbohydrates with digestion characteristics between those of lente uncooked starches and rapidly digestible oligosaccharides were administered in a dose of 1.5 g/kg body weight to five patients with glycogenosis from glucose-6-phosphatase deficiency. Postprandial duration of normoglycemia and concentrations of blood insulin and lactate were determined. Uncooked barley groats in water, or incorporated in a meal turned out to behave as lente carbohydrates. Uncooked couscous in water, couscous incorporated in a meal, and partially cooked macaroni given as a meal behaved as semilente carbohydrates as compared with uncooked cornstarch and glucose. The in vitro determination of the digestibility index along with the in vivo tolerance test enables us to choose and incorporate semilente carbohydrates in the day-time treatment of patients.

Impaired muscle glycogen storage after muscle biopsy

To assess the effects of repeated needle biopsies on the rate of muscle glycogen repletion, eight male subjects were studied immediately after and 2 days after an exhaustive cycling bout. A single biopsy was obtained from the right vastus lateralis muscle immediately after an exhaustive cycling bout. Two days later, a sample was taken 1 cm lateral or medial to sample A. In four of these subjects, additional biopsies were taken 3 cm distal and proximal. A control specimen was also taken from the left leg 2 days after the exercise. Ten days after the exercise, muscle was again sampled from each leg of these four subjects. Analysis of these samples revealed that the initial biopsy impaired glycogen storage in the muscle taken 1 cm medial or lateral to the previous site. This reduction in glycogen storage was most pronounced in the first 2 days after the exercise. Samples taken distal and proximal to the initial biopsy contained, on the average, less glycogen than the contralateral leg, but these differences were only significantly different in the distal muscle sample. Alteration in muscle glycogen storage was seen to persist for 10 days after the first biopsy, suggesting that care must be taken in selecting the site for repeated biopsies from the same muscle.

Aberrant regulation of carbohydrate metabolism and metamorphosis during renal carcinogenesis

Systematic studies of the sequence of cellular changes during renal carcinogenesis induced in rats by stop experiments with N-nitrosomorpholine or streptozotocin and of human renal cell carcinomas led to the following main results and conclusions: All types of epithelial kidney tumors known from human pathology, namely clear-cell, acidophilic (granular), basophilic, chromophobic and oncocytic tumors, can be induced by the chemicals. Phenotypically altered epithelia resembling those in the tumors appear in single or multiple tubules long before unequivocal tumors develop. The progression from the preneoplastic tubular lesions to the tumors is an autogenous process which is independent of the further action of the carcinogen. At least three different types of tubular lesions can be distinguished: (a) Clear cell tubules storing glycogen in excess, (b) chromophobic or basophilic tubules frequently accumulating acid mucopolysaccharides (glycosaminoglycans, proteoglycans), and (c) oncocytic tubules accumulating atypical mitochondria. Whereas the precise site of origin of the clear cell tubules within the nephron remains unclear, the fine structural and cytochemical findings suggest that the chromophobic and basophilic tubules originate from the proximal and the oncocytic tubules from the distal nephron. Each type of tubular lesion is apparently the precursor of a cytologically specific tumor type. The well-known aberration in carbohydrate metabolism in renal tumors might occur in response to a carcinogen-induced metabolic derangement which is frequently associated with excessive storage of polysaccharides or lipids persisting for weeks and months until fast-growing tumors appear. Whereas the primary biochemical lesion leading to the persisting storage phenomena is most probably fixed at the genetic level, epigenetic changes, namely an adaptation of cellular enzymes gradually activating alternative metabolic pathways, might be responsible for the ultimate neoplastic transformation of the cell.

Glycogenosis due to liver and muscle phosphorylase kinase deficiency

A four-year-old Israeli Arab boy was found to have glycogen accumulation in both liver and muscle without clinical symptoms. Liver phosphorylase kinase (PK) activity was 20% of normal, resulting in undetectable activity of phosphorylase a. Muscle PK activity was about 25% of normal, resulting in a marked decrease of phosphorylase a activity. Two sisters showed a similar pattern, whereas one brother had normal PK activity. The patient's liver protein kinase activity was normal Addition of exogenous protein kinase did not affect PK activity, whereas exogenous PK restored phosphorylase activity to normal. These findings indicate that these patients are affected by a rare variant of PK deficiency, which involves both muscle and liver and which apparently is not sex linked. It is possible that this defect represents an unusual mutation of a subunit of the phosphorylase kinase enzyme.

Liver glycogenosis caused by a defective phosphorylase system: hemolysate analysis

Investigated were 24 cases of glycogenosis caused by a reduction in liver phosphorylase activity. The intravenous glucagon tolerance test could not discriminate between phosphorylase kinase deficiency [glycogen storage disease (GSD) IX] and phosphorylase deficiency (GSD VI). These two subgroups were distinguished by hemolysate enzyme assays: (1) GSD IX was characterized by a residual phosphorylase kinase activity, a low activation curve for endogenous phosphorylase b and increased amylo-1,6-glucosidase activity. (2) GSD VI was characterized by a normal or increased phosphorylase kinase activity, a slight activation of endogenous phosphorylase b and a normal amylo-1,6-glucosidase activity.

Myophosphorylase deficiency: two different molecular etiologies

Two different forms of myophosphorylase deficiency (McArdle's disease) can be distinguished through the presence or absence of the protein subunit corresponding to phosphorylase in muscle extracts analyzed by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Two patients showed a complete absence of the phosphorylase protein subunit, while another patient had an increased quantity of an apparently defective phosphorylase protein subunit. On the basis of these observations, the existence of two distinct subtypes of phosphorylase deficiency can be inferred.

[Phospho-hexo-isomerase deficiency]

Hematologic, genetic and biochemical data of two patients suffering from glucosephosphate isomerase deficiency are described. In one of them a generalized deficiency could be demonstrated. The molecular instability of the deficient enzyme results in early inactivation. Its consequences for carbohydrate metabolism are exposed. Besides a non-spherocytic hemolytic anemia, a hepatic glycogenosis could be observed. Our patients are compared to litterature.

The clinical approach to neurologic disorders

The role of the clinician in the study of genetically determined disorders of the nervous system is to detect and describe clinical syndromes. His tools are the history and the physical examination. His task is to recognize those striking signs or symptoms, or those significant collections of lesser findings, which suggest a new disease state. His greatest responsibility is to weigh the significance of such findings against the effects of human variation, growth, maturation and senescence, and the life situation of the patient or his family. His unique contribution is his ability to recognize and pursue the uncertain entity, until chance observation, the evolution of the illness, or new technics of study make its exegesis possible.

New aspect of hepatic nuclear glycogenosis in diabetes

Three cases of nuclear glycogenosis in the liver of diabetic patients have been studied by electron microscopy. In addition to the glycogen deposits described by others, an unusual intranuclear glycogen-filled body was found in all three cases. This body occurred alone or in close contact with the major glycogen deposit.

Chloroquine myopathy

Images

Generalized glycogenosis in siblings

Images