Mutations in the liver glycogen synthase gene in children with hypoglycemia due to glycogen storage disease type 0.

Glycogen storage disease type 0 (GSD-0) is a rare form of fasting hypoglycemia presenting in infancy or early childhood and accompanied by high blood ketones and low alanine and lactate concentrations. Although feeding relieves symptoms, it often results in postprandial hyperglycemia and hyperlactatemia. The glycogen synthase (GS) activity has been low or immeasurable in liver biopsies, whereas the liver glycogen content has been only moderately decreased. To investigate whether mutations in the liver GS gene (GYS2) on chromosome 12p12.2 were involved in GSD-0, we determined the exon-intron structure of the GYS2 gene and examined nine affected children from five families for linkage of GSD-0 to the GYS2 gene. Mutation screening of the 16 GYS2 exons was done by single-strand conformational polymorphism (SSCP) and direct sequencing. Liver GS deficiency was diagnosed from liver biopsies (GS activity and glycogen content). GS activity in the liver of the affected children was extremely low or nil, resulting in subnormal glycogen content. After suggestive linkage to the GYS2 gene had been established (LOD score = 2.9; P < 0.01), mutation screening revealed several different mutations in these families, including a premature stop codon in exon 5 (Arg246X), a 5'-donor splice site mutation in intron 6 (G+1T--> CT), and missense mutations Asn39Ser, Ala339Pro, His446Asp, Pro479Gln, Ser483Pro, and Met491Arg. Seven of the affected children carried mutations on both alleles. The mutations could not be found in 200 healthy persons. Expression of the mutated enzymes in COS7 cells indicated severely impaired GS activity. In conclusion, the results demonstrate that GSD-0 is caused by different mutations in the GYS2 gene.

The importance of nucleoside triphosphate inhibition of liver glycogen synthase phosphatase activity.

The liver glycogen particle contains constitutive glycogen-synthase phosphatase activity which is inhibited by ATP-Mg in a concentration-dependent manner within the physiological range (I0.5 = 0.1 mM). Therefore, we determined whether other nucleoside triphosphate-magnesium complexes also inhibit synthase phosphatase activity. UTP-Mg, CTP-Mg and GTP-Mg were all found to be inhibitory. The maximum inhibition was 85-90% which was greater than that for ATP-Mg. The I0.5 for UTP-Mg was comparable to that of ATP-Mg but it was greater for CTP-Mg and for GTP-Mg. At in vivo physiological concentrations, both UTP and ATP are possible inhibitors of synthase phosphatase activity. In the presence of a saturating concentration of ATP-Mg, added UTP-Mg increased the inhibition suggesting the presence of at least two distinct nucleotide binding sites. Substitution of calcium for magnesium in an ATP complex had no effect on the I0.5, but increased the maximum inhibition. The present studies also suggest that in the multistep conversion of synthase D to synthase I, ATP-Mg inhibition occurs early in the sequence. Addition of glycogen, a known inhibitor of synthase phosphatase activity, to a reaction mixture containing 3 mM ATP-Mg did not further inhibit synthase phosphatase activity when added at concentrations up to 22 mg/ml. The latter data suggest that the presence of a nucleoside triphosphate may desensitize the phosphatase to glycogen inhibition. ATP-Mg and, to a lesser extent, UTP-Mg and CTP-Mg all stimulated phosphorylase phosphatase activity but GTP-Mg did not.

Evidence for the non-identity of proteins having synthase phosphatase, phosphorylase phosphatase and histone phosphatase activity in rat liver.

Synthase phosphatase, phosphorylase phosphatase and histone phosphatase in rat liver were measured using as substrates purified liver synthase D, phosphorylase alpha and 32P-labelled phosphorylated f1 histone, respectively. The three phosphatase enzymes had different sedimentation characteristics. Both synthase phosphatase and phosphorylase phosphatase were found to sediment with the microsomal fraction under our experimental conditions. Only 10% of histone phosphatase was in this fraction; the majority was in the cytosol. No change in histone phosphatase was observed in the adrenalectomized fasted rat whereas synthase phosphatase and phosphorylase phosphatase activities were decreased 5-10 fold. Fractionation of liver extract with ethanol produced a dissociation of the three phosphatase activities. When a partially purified fraction was put on a DEAE-cellulose column, synthase phosphatase and phosphorylase phosphatase both exhibited broad elution profiles but their activity peaks did not coincide. Histone phosphatase eluted as a single discrete peak. When the supernatant of CaCl2-treated microsomal fraction was put on a Sepharose 4B column, the majority of synthase phosphatase was found to elute with the larger molecular weight proteins whereas the majority of phosphorylase phosphatase eluted with the smaller species. Histone phosphatase migrated as a single peak and was of intermediate size. Synthase phosphorylase phosphatase by synthase D (Ki approximately 2 units/ml). The inhibition of synthase phosphatase by phosphorylase alpha was kinetically non-competitive with substrate. Histone phosphatase activity was not inhibited by synthase D or by phosphorylase alpha. The above results suggest that different proteins are involved in the dephosphorylation of synthase D, phosphorylase alpha and histone in the cell.

Characteristics of the dephosphorylated form of phosphorylase purified from rat liver and measurement of its activity in crude liver preparations.

The phosphorylated form of liver glycogen phosphorylase (alpha-1,4-glucan : orthophosphate alpha-glucosyl-transferase, EC 2.4.1.1) (phosphorylase a) is active and easily measured while the dephosphorylated form (phosphorylase b), in contrast to the muscle enzyme, has been reported to be essentially inactive even in the presence of AMP. We have purified both forms of phosphorylase from rat liver and studied the characteristics of each. Phosphorylase b activity can be measured with our assay conditions. The phosphorylase b we obtained was stimulated by high concentrations of sulfate, and was a substrate for muscle phosphorylase kinase whereas phosphorylase a was inhibited by sulfate, and was a substrate for liver phosphorylase phosphatase. Substrate binding to phosphorylase b was poor (KM glycogen = 2.5 mM, glucose-1-P = 250 mM) compared to phosphorylase a (KM glycogen = 1.8 mM, KM glucose-1-P = 0.7 mM). Liver phosphorylase b was active in the absence of AMP. However, AMP lowered the KM for glucose-1-P to 80 mM for purified phosphorylase b and to 60 mM for the enzyme in crude extract (Ka = 0.5 mM). Using appropriate substrate, buffer and AMP concentrations, assay conditions have been developed which allow determination of phosphorylase a and 90% of the phosphorylase b activity in liver extracts. Interconversion of the two forms can be demonstrated in vivo (under acute stimulation) and in vitro with little change in total activity. A decrease in total phosphorylase activity has been observed after prolonged starvation and in diabetes.

Regulation of synthase phosphatase and phosphorylase phosphatase in rat liver.

Using substrates purified from liver, the apparent Km values of synthase phosphatase ([UDPglucose--glycogen glucosyltransferase-D]phosphohydrolase, EC 3.1.3.42) and phosphorylase phosphatase (phosphorylase a phosphohydrolase, EC 3.1.3.17) were found to be 0.7 and 60 units/ml respectively. The maximal velocity of phosphorylase phosphatase was more than a 100 times that of synthase phosphatase. In adrenalectomized, fasted animals there was a complete loss of synthase phosphatase but only a slight decrease in phosphorylase phosphatase when activity was measured using endogenous substrates in a concentrated liver extract. When assayed under optimal conditions with purified substrates, both activities were present but had decreased to very low levels. Mixing experiments indicated that synthase D present in the extract of adrenalectomized fasted animals was altered such that it was no longer a substrate for synthase phosphatase from normal rats. Phosphorylase a substrate on the other hand was unaltered and readily converted. When glucose was given in vivo, no change in percent of synthase in the I form was seen in adrenalectomized rats but the percent of phosphorylase in the a form was reduced. Precipitation of protein from an extract of normal fed rats with ethanol produced a large activation of phosphorylase phosphatase activity with no corresponding increase in synthase phosphatase activity. Despite the low phosphorylase phosphatase present in extracts of adrenalectomized fasted animals, ethanol precipitation increased activity to the same high level as obtained in the normal fed rats. Synthase phosphatase and phosphorylase phosphatase activities were also decreased in normal fasted, diabetic fed and fasted, and adrenalectomized fed rats. Both enzymes recovered in the same manner temporally after oral glucose administration to adrenalectomized, fasted rats. These results suggest an integrated regulatory mechanism for the two phosphatase.

Characterization of the glycogen synthase D found in liver of the adrenalectomized fasted rats.

We have previously shown that the synthase D (UDPglucose:glycogen 4-alpha-D-glucosyltransferase, EC 1.4.1.11) present in the liver of the adrenalectomized fasted rat was not converted to synthase I by synthase phosphatase from normal animals, suggesting the presence of a non-substrate form of synthase D (Tan, A.W.H. and Nuttall, F.Q. (1976) Biochim. Biophys. Acta 445, 118--130). The enzymatic properties of this synthase D have now been examined. Using optimal assay conditions, the total amount of synthase D activity in the adrenalectomized fasted rats was similar to that of normal fed rats when 1% glycogen was included in the homogenizing buffer. However, the two enzymes appeared to have different affinities for the substrate, UDPglucose and the modifier, glucose-6-P. The changes in kinetic properties were not due to differences in glycogen or to a dialyzable modifier in the extracts. Synthase D from adrenalectomized fasted and from normal fed rats was partially purified. After DEAE-cellulose chromatography, modification appeared to have occurred such that the enzyme from the adrenalectomized fasted rat had properties similar to that of the normal fed rat. The enzymes were cold-labile, had different properties from enzymes in the crude extract and they were both converted to synthase I by synthase phosphatase. We conclude from these studies that the phosphorylation site in the synthase is in a flexible region of the protein. Changes in the ability of the synthase D to interact and be dephosphorylated by synthase phosphatase can occur readily in vivo and in vitro. The molecular basis for the modification remains unknown.

Dietary fiber in the management of diabetes.

It generally is accepted that a diet high in fiber, particularly soluble fiber, is useful in the management of the plasma glucose concentration in individuals with diabetes. This is one of the reasons several national diabetes associations have recommended that diabetic individuals ingest a diet high in fiber-containing foods. However, more recent data obtained in carefully controlled studies with more definitive end points, indicate this may not be the case. It has been shown clearly that addition of water-soluble, gel-forming fiber in the form of guar gum and perhaps gum tragacanth to an ingested glucose solution or to a mixed meal will reduce the expected rise in glucose concentration. This has been demonstrated in both normal subjects and subjects with IDDM and NIDDM. However, it is only observed when large amounts of fiber are added. The fiber also must be mixed with the administered glucose or food. Other less viscous soluble fiber sources such as the pectins and psyllium powder are not effective. In long-term, well-controlled trials, guar gum, pectin, beet fiber, or cereal bran fiber ingested with meals has been of little or no value in controlling the plasma glucose concentration in individuals with NIDDM. Several studies have been conducted in which a high-carbohydrate diet has been reported to reduce the plasma glucose concentration. In these diets, foods with a high fiber content have been emphasized. In general, they were not well controlled, and several confounding variables such as weight loss, decreased food energy intake, different food sources with potential for differences in starch digestibility, and decreased dietary fat content were present.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of hepatic glucose uptake to intrahepatic glucose concentration in fasted rats after glucose load.

Glucose concentration gradients across the liver and hepatic blood flow were measured to characterize the relationship of hepatic glucose uptake to hepatic glucose concentration for 240 min after administration of a large oral glucose load to fasted rats. Extraction of glucose occurred only transiently, from 20 to 80 min after glucose administration. The liver changed from net glucose output to net glucose removal only when the intracellular hepatic glucose concentration exceeded 12.5 mumol/ml water. Even when arteriovenous glucose concentrations gradients were compatible with net direct hepatic uptake of glucose, the hepatic glucose concentration always exceeded the inflow glucose concentration. These data indicate that direct glucose uptake occurred against a concentration gradient when the liver is considered as a whole. The hepatic intracellular-to-extracellular glucose concentration gradient changed very little, suggesting that this is not being regulated by glucose, insulin, or other effectors. The mechanism by which the hepatic glucose concentration and net hepatic glucose uptake versus output are coordinated is unknown. The rate of glycogen synthesis was linear for 120 min after administration of the glucose load. This occurred in the presence of direct uptake of glucose early in the time course and later in the presence of net glucose output by the liver. Net direct uptake of glucose by the liver could account for, at most, 37-55% of the glycogen formed. Fractional extraction of both lactate and alanine decreased after glucose was given, but net hepatic uptake of these metabolites could account for 33-49 and 7-10%, respectively, of the glycogen formed, depending on plasma versus blood water flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of diabetes mellitus in school-age children in Minnesota.

The prevalence of diabetes in Minnesota school-age children was found to be one per 529 students (1.89 per 1,000), 95 per cent of whom were receiving insulin. Data were obtained by a mail survey of the public schools in the state. Enrollment in public schools represents 90 per cent of the student population in Minnesota, and data were received from 96 per cent of the public schools. This return rate by schools accounts for 95 per cent of the total student enrollment. Diabetes increased linearly with age, representing a yearly prevalence increase of 0.16 cases per 1,000 students.

Mechanism of stimulation of liver glycogen synthesis by fructose in alloxan diabetic rats.

In diabetic animals and humans, stimulation of liver glycogen synthesis has been reported after administration of a large parenteral fructose load. The effects of an oral fructose load have not been examined previously. In the diabetic state, glycogen synthase phosphatase activity is reduced, and synthase D (the inactive form) is a poor substrate for the phosphatase. Thus, activation of synthase to the synthase R and synthase I (R + I) (active) forms by fructose would not be expected. We have determined that oral fructose administration does stimulate glycogen synthesis and have examined the mechanism by which this is accomplished. In 24-h-fasted alloxan diabetic rats, basal liver glycogen was higher than in normal rats (8.3 +/- 1.8 vs. 3.0 +/- 0.5 mg/g wet wt). After fructose (4 g/kg) was given, the initial rate of glycogen synthesis was normal in diabetic rats, but total glycogen synthesis was reduced. By 240 min, liver glycogen increased to 18 +/- 4.0 mg/g wet wt in diabetic rats versus 30.5 +/- 1.5 mg/g wet wt in normal rats. Synthase R + I was low and did not increase significantly (0.063 +/- 0.006 to 0.064 +/- 0.010 U/g wet wt) after fructose administration to the diabetic animals. Phosphorylase a did not decrease significantly during the period of active glycogen synthesis. In the diabetic rats, glucose-6-phosphate increased by 84% (0.103 +/- 0.010 to 0.184 +/- 0.020 mumol/g wet wt) within 10 min and remained elevated above the control level. UDPglucose decreased from 0.336 +/- 0.013 to 0.271 +/- 0.011 mumol/g wet wt at 10 min and remained below the control level.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral protein hydrolysate causes liver glycogen depletion in fasted rats pretreated with glucose.

Studies in rats indicated that the major physiologic stimulus for synthesis of liver glycogen is a rise in the portal glucose concentration after ingestion of a meal. Conversely, glycogen degradation in the liver is stimulated by a rise in portal glucagon concentration. In humans, ingestion of carbohydrate lowers the concentration of circulating glucagon, whereas protein stimulates an increase in peripheral glucagon concentration. Little is known about the effects of these nutrients on glucagon concentrations in the rat. Therefore, we studied the effects of oral protein administration to 24-h-fasted rats pretreated with glucose for 2 h to test the effect of two potent but potentially opposite signals for glycogen metabolism. An increase in liver glycogen concentration was observed in fasted rats given oral glucose, as expected. Removal of glucose by the liver could not account for the glycogen synthesized, indicating that most glycogen formed was derived from gluconeogenesis. In addition, the apparent intracellular and extracellular glucose concentrations were not in equilibrium. A small amount of glucose may have been taken up against a concentration gradient. The portal glucagon was not significantly decreased. Oral protein administration to the rats pretreated with glucose resulted in a rapid and dramatic decrease in liver glycogen concentration. This was associated with an increase in the portal glucagon concentration, no change in insulin concentration, a slight increase in liver cAMP concentration, an increase in the active form of phosphorylase, and a decrease in the active form of synthase. Glycogenolysis could account for the glucose released into the circulation from the liver after protein administration.

Thin muscle capillary basement membranes in myotonic dystrophy.

Muscle capillary basement membrane width (MCBMW) was measured in 18 myotonic dystrophy patients and compared with that in age- and sex-matched normal and diabetic subjects. The MCBMW in myotonic dystrophy patients (773 +/- 258 A) was significantly thinner than in normal subjects (925 +/- 181 A, P less than 0.05) or in diabetics (1224 +/- 614 A, P less than 0.01). An increase in MCBMW with advancing age was present in all groups but was greatest in the myotonic dystrophy groups (r = +0.59, P less than 0.01). There was no relation between MCBMW and either the degree of glucose intolerance or insulin hypersecretion in the myotonic dystrophy group, though none had fasting hyperglycemia. This is the first report of a condition associated with thinner-than-normal capillary basement membrane.

Gynecomastia and cirrhosis of the liver.

Hepatic cirrhosis is frequently listed as a cause of gynecomastia. We found previously that in hospitalized men the prevalence of gynecomastia was correlated with body mass index and with age. The mean body mass index and the prevalence of gynecomastia in the cirrhotic subjects (nonedematous) did not differ from those in the overall population. Because more severely cirrhotic subjects with ascites, peripheral edema, or both usually are thin, we examined 18 more severely cirrhotic subjects and 18 nonobese (mean body mass index, 20.9 +/- 0.6 kg/m2), age-matched control subjects for the prevalence of palpable gynecomastia. Total testosterone, free testosterone, total estrogen, and estradiol concentrations also were measured. Fifty percent of the control subjects had gynecomastia. Breast tissue diameter was correlated with body mass index. The prevalence of gynecomastia in the cirrhotic subjects was 44%. In these subjects no significant correlation was noted between breast tissue diameter and body mass index, presumably because the body mass index was increased owing to fluid retention. The results could not be accounted for based on medications. Serum free testosterone concentrations were lower in the cirrhotic patients than in the controls (0.11 +/- 0.02 vs 0.22 +/- 0.03 nmol/L). The total estrogen-free testosterone ratio was higher in cirrhotic patients (10.3 +/- 2.5 vs 2.6 +/- 0.5), as was the estradiol-free testosterone ratio (2.2 +/- 0.7 vs 0.5 +/- 0.1). These ratios did not differ significantly in cirrhotic subjects with and without gynecomastia. Therefore, these data indicate that factors other than the estrogen-testosterone ratio are playing a role in the development of gynecomastia in both cirrhotic subjects and controls or that breast tissue sensitivity to an elevated estrogen-testosterone ratio is highly varible.

Adult hereditary fructose intolerance.

Hereditary fructose intolerance was diagnosed in a 69-year-old man on the basis of his medical history and the response to an intravenous fructose tolerance test. Three men of the same age as our patient were used as control subjects. Since the severity may vary and affected individuals self-impose fructose and sucrose restriction, they are essentially symptom free. The diagnosis can only be suspected by taking a careful dietary history. The prevalence of this condition in adults is unknown. It is rare but is likely to be more common than data in the literature would indicate.

Effect of phosphate or magnesium cathartics on serum calcium: observations in normocalcemic patients.

The administration of commercial phosphate cathartic in conventional doses to normal subjects prior to barium enema resulted in a striking increase in serum phosphorus levels followed by a decline in serum calcium levels in all subjects. Changes were highly significant (P less than .01) when compared with control subjects who were prepared for the same procedure with magnesium citrate. Levels of serum potassium also decreased significantly (P less than .01) but not serum sodium, chloride, bicarbonate, or magnesium.

Thyroid function after radiation and surgery for head and neck cancer.

Preoperative radiation followed by surgical excision is accepted therapy for head and neck cancer. The effects of these modalities on thyroid function were evaluated in a prospective study. Sixty-one patients were given cobalt 60 radiation. Results showed that 41 patients (67%) were euthyroid, 12 patients (20%) were clinically and chemically hypothyroid, and 8 patients (13%) had transient loss of thyroid reserve. Permanent hypothyroidism occurred frequently in patients with hemithyroidectomy, but rarely in those treated with radiation alone. Onset of hypothyroidism was zero to six months, with transient loss of thyroid reserve occurring up to 18 months. This constitutes the initial report of an ongoing systematic study of thyroid function in such patients. The high incidence of hypothyroidism indicates a need for careful periodic evaluation.

Histiocytosis X and compulsive water drinking: report of a case.

We describe a patient with histiocytosis X and compulsive water drinking. The association of diabetes insipidus with histiocytosis X is well recognized, and this patient was initially considered to have diabetes insipidus. It was only after further testing that the proper diagnosis was made.

Diet and the diabetic patient.

At the present time, our knowledge regarding the metabolic consequences of various dietary regimens is incomplete and in need of further research. In addition, the composition of a diet for diabetic persons that will result in the best blood glucose control is uncertain and controversial. Whether dietary changes can significantly delay or prevent the long-term complications of diabetes also is not known. Thus, the insistence that certain foods be avoided by the diabetic person or that a specified diet be adhered to rigidly cannot be defended scientifically. In view of the above limitations in our knowledge, perhaps the best approach should be to allow diabetic persons to select their own diet and daily meal plan, as long as the nutrient content is adequate. A diabetic person being treated with insulin or a hypoglycemic drug will have to comply with a dietary regimen consistent in carbohydrate content and time of meal ingestion. This continues to be of vital importance in the management plan. Nevertheless, an insulin or drug regimen usually can be designed to accommodate the individual's usual eating habits and food preferences. Such a flexible approach to diet management should lead to better patient compliance and overall management of the diabetic patient.

Comparison of percent total GHb with percent HbA1c in people with and without known diabetes.

OBJECTIVE: To directly compare results obtained using an ion-exchange high-performance liquid chromatography (HPLC) HbA1c method used in the Diabetes Control and Complications Trial with two different affinity chromatography methods in which "total GHb" is determined. RESEARCH DESIGN AND METHODS: Blood was obtained from a large number of people with and without known diabetes. The specimens were divided and assayed for HbA1c and for total GHb. Total GHb was determined using a semi-automated gravity-elution boronate affinity chromatography method and an automated boronate affinity HPLC method. The results obtained with the two methods were also compared. RESULTS: In subjects without known diabetes, the mean percentage HbA1c and the range of values were similar to the total GHb values in the same subjects when assayed using the semi-automated affinity gravity-elution method (mean 5.2 +/- 0.4 and 5.1 +/- 0.4% [SD], respectively). With the affinity HPLC method, results were 5.3 +/- 0.4%. The similarity in results was surprising. However, analysis of the data suggests that a large proportion of the material in the HbA1c fraction measured using this ion-exchange HPLC method is not GHb, as pointed out by others. Although the results were similar in people without known diabetes, in the people with diabetes, the incremental increase was approximately 25% greater for the total GHb when compared with the increase in HbA1c. When corrected for the non-GHb being measured by the HbA1c method, it can be calculated that approximately 40% more GHb is measured using affinity chromatography over the entire range of GHb values. CONCLUSIONS: The similarity in the mean and range of percent HbA1c and in percent total GHb using these different methods can be attributed to two factors: 1) the HbA1c ion-exchange method measures only approximately 50-60% of the total GHb present, and 2) approximately 40-50% of the material being measured in the HbA1c fraction is not GHb, i.e., offsetting factors fortuitously resulted in values similar to the more specific affinity methods. The greater incremental increase in percent total GHb compared with percent HbA1c in people with diabetes can be attributed to the greater amount of GHb being measured with the affinity methods.

Quantitative importance of dietary constituents other than glucose as insulin secretagogues in type II diabetes.

In seven type II (non-insulin-dependent) diabetic patients, given either 50 g glucose or a mixed meal potentially containing 61 g glucose as starch and sucrose, the postmeal plasma glucose area integrated over 4 h was less after the mixed meal. The insulin area was considerably greater (2.1-fold). The greater increase in insulin could be explained largely, but not entirely, by the protein and fructose in the mixed meal (85%) which, in addition to glucose, are known insulin secretagogues. The residual unexplained increase may be due to a synergistic interaction of these secretagogues, an unidentified insulin secretagogue, or by a reduced insulin removal rate. These possibilities remain to be explored.