Pathologic studies of the osteoporosis of Von Gierke's disease (glycogenosis 1a)

Glycogen storage disease type 1a is associated with disturbed vitamin A metabolism and elevated serum retinol levels

Glycogen storage disease type 1a (GSD Ia) is an inborn error of metabolism caused by mutations in the G6PC gene, encoding the catalytic subunit of glucose-6-phosphatase. Early symptoms include severe fasting intolerance, failure to thrive and hepatomegaly, biochemically associated with nonketotic hypoglycemia, fasting hyperlactidemia, hyperuricemia and hyperlipidemia. Dietary management is the cornerstone of treatment aiming at maintaining euglycemia, prevention of secondary metabolic perturbations and long-term complications, including liver (hepatocellular adenomas and carcinomas), kidney and bone disease (hypovitaminosis D and osteoporosis). As impaired vitamin A homeostasis also associates with similar symptoms and is coordinated by the liver, we here analysed whether vitamin A metabolism is affected in GSD Ia patients and liver-specific G6pc^−/− knock-out mice. Serum levels of retinol and retinol binding protein 4 (RBP4) were significantly increased in both GSD Ia patients and L-G6pc^−/− mice. In contrast, hepatic retinol levels were significantly reduced in L-G6pc^−/− mice, while hepatic retinyl palmitate (vitamin A storage form) and RBP4 levels were not altered. Transcript and protein analyses indicate an enhanced production of retinol and reduced conversion the retinoic acids (unchanged LRAT, Pnpla2/ATGL and Pnpla3 up, Cyp26a1 down) in L-G6pc^−/− mice. Aberrant expression of genes involved in vitamin A metabolism was associated with reduced basal messenger RNA levels of markers of inflammation (Cd68, Tnfα, Nos2, Il-6) and fibrosis (Col1a1, Acta2, Tgfβ, Timp1) in livers of L-G6pc^−/− mice. In conclusion, GSD Ia is associated with elevated serum retinol and RBP4 levels, which may contribute to disease symptoms, including osteoporosis and hepatic steatosis.

Bone mineral density in children, adolescents and adults with glycogen storage disease type Ia: a cross-sectional and longitudinal study

The occurrence of (symptoms related to) osteopenia is a known complication in glycogen storage disease type Ia (GSD Ia) patients. However, only limited information is available about bone mineral density (BMD). Using dual energy x-ray absorptiometry, we studied both cross-sectional and longitudinal lumbar spine areal BMD (BMD(areal) in g/cm2), areal BMD corrected for delayed bone maturation (BMD(bone age) in g/cm2), and volumetric BMD (BMD(vol) in g/cm3). Prepubertal GSD Ia patients (n = 8) had normal BMD (median z-scores BMD(areal) -0.6, BMD(bone age) -0.5 and BMD(vol) -0.5), whereas adolescent patients (n = 12) and adult patients (n = 9) had significantly reduced BMD (BMD(areal) -2.3, BMD(bone age) -1.6, BMD(vol) -2.0, and BMD(areal) -1.9, BMD(vol) -1.5, respectively). Our longitudinal study, showing a stable BMD(areal) but a trend to a decrease in BMD(vol) in prepubertal patients during follow-up, did not clarify whether the difference in BMD between prepubertal and adolescent/adult patients reflects a diminished accretion of BMD during childhood or reflects historical differences in treatment. In adolescent and adult GSD Ia patients, BMD(areal) and BMD(vol) were reduced but stable during follow-up. Especially patients with delayed bone maturation were at risk for reduced BMD. No correlation between parameters of metabolic control and BMD could be detected. Daily calcium intake was within recommended allowances ranges. Abnormal biochemical results included hypomagnesaemia (29%), hypercalciuria (34%) and reduced tubular resorption of phosphate (21%). Although the underlying pathophysiology of reduced BMD in GSD Ia remains unsolved, metabolic control should be optimized to correct as much as possible metabolic and endocrine abnormalities that may influence both bone matrix formation and bone mineral accretion.

Low bone mass in glycogen storage disease type 1 is associated with reduced muscle force and poor metabolic control

OBJECTIVE

To study the relation between muscle force, bone mass, and metabolic control in patients with glycogen storage disease type (GSD 1).

STUDY DESIGN

Distal radius bone mass and density were evaluated in 19 patients with GSD 1 (15 GSD 1a, 4 GSD 1b) by means of peripheral quantitative computed tomography. Grip force was quantified with a dynamometer.

RESULTS

Height, weight, bone mass, and grip force were significantly decreased in the patients with GSD 1a, mainly as the result of low values in the poorly controlled subgroup. Boys had lower bone mass than girls. Patients with GSD 1b had higher values for bone mineral density in the trabecular compartment. In most of the study participants bone mass appeared to be adequately adapted to the mechanical requirements imposed by muscle contraction. However, 3 patients with GSD 1a had evidence for a low bone mass.

CONCLUSIONS

In GSD 1, both reduced muscle strength and a direct disease effect can contribute to low bone mass. The quality of treatment is crucial to prevent disturbances in musculoskeletal development.

Glycogen storage diseases. Phenotypic, genetic, and biochemical characteristics, and therapy

The glycogen storage diseases are caused by inherited deficiencies of enzymes that regulate the synthesis or degradation of glycogen. In the past decade, considerable progress has been made in identifying the precise genetic abnormalities that cause the specific impairments of enzyme function. Likewise, improved understanding of the pathophysiologic derangements resulting from individual enzyme defects has led to the development of effective nutritional therapies for each of these disorders. Meticulous adherence to dietary therapy prevents hypoglycemia, ameliorates the biochemical abnormalities, decreases the size of the liver, and results in normal or nearly normal physical growth and development. Nevertheless, serious long-term complications, including nephropathy that can cause renal failure and hepatic adenomata that can become malignant, are a major concern in GSD-I. In GSD-III, the risk for hypoglycemia diminishes with age, and the liver decreases in size during puberty. Cirrhosis develops in some adult patients, and progressive myopathy and cardiomyopathy occur in patients with absent GDE activity in muscle. It remains unclear whether these complications of glycogen storage disease can be prevented by dietary therapy. Glycogen storage diseases caused by lack of phosphorylase activity are milder disorders with a good prognosis. The liver decreases in size, and biochemical abnormalities disappear by puberty.

Calcium kinetics in glycogen storage disease type 1a

Glycogen storage disease type 1a (Von Gierke's disease) is one of the more common glycogen storage diseases (GSD). GSD 1a patients can have severe idiopathic osteopenia, often beginning at a young age. Since calcium tracer studies offer a sensitive probe of the bone microenvironment and of calcium deposition, kinetics might be disturbed in patients with GSD 1a. Plasma dilution kinetics obtained using the stable isotope 42Ca are shown in this paper to be quite different between GSD 1a patients and age-matched controls. Comparison of kinetic parameters in these two populations is made using a new binding site model for describing calcium dynamics at the plasma-bone interface. This model describes reversible binding of calcium ions to postulated short-term and long-term sites by a retention probability density function psi (t). Using this analysis, adult GSD subjects exhibited a significant decrease (P = 0.023) in the apparent half-life of a calcium ion on the longer-term site compared with controls. The general theory of calcium tracer dilution kinetics is then discussed in terms of a new model of short-term calcium homeostasis recently proposed by Bronner and Stein [5].

Bone mineralisation in type 1 glycogen storage disease

Radial bone mineral content (BMC) was measured using single photon absorptiometry in 11 prepubertal children, aged 3.4-12.6 years, with glycogen storage disease type 1 (GSD-1), 2 of whom were receiving granulocyte colony stimulating factor (G-CSF) therapy for chronic neutropenia. Patients were short (median height SD score -1.35, range -3.74 to -0.27), and had reduced BMC Z scores (median 1.79, range -6.35 to +0.27) and radial bone width Z scores (median -0.72, range -2.00 to +0.68). Those receiving G-CSF did not differ significantly from the rest of the group. Generally dietary calcium intake was low and urinary calcium excretion increased. Urinary lactate excretion was high but did not correlate with BMC Z scores. Factors regulating bone metabolism (parathyroid hormone and 25-hydroxy vitamin D concentrations) and markers of bone formation (osteocalcin and skeletal alkaline phosphatase) were not increased implying that there was no compensation for increased bone resorption.

CONCLUSION

Patients with GSD-1 may be at increased risk of fracture in later life and require close attention to metabolic control and calcium balance.

The hepatic glycogen storage diseases--problems beyond childhood

The introduction of continuous nocturnal enteral glucose feeds and uncooked cornstarch has improved the prognosis for patients with the hepatic glycogen storage diseases. An increasing number of patients are surviving into adulthood in better health, but still at some medical cost. In this review we examine bone mineralization, renal function, hepatic tumours, and vascular endothelial function in GSD I and cardiac function in GSD III. All females over the age of 5 years with GSD I, III, VI and IX had morphologically polycystic ovaries. Thirteen adult GSD I patients have been studied, and been found to have poor bone mineralization and marked renal glomerular and tubular dysfunction. More than half of these patients also had focal hepatic lesions on sonography and yet vascular endothelial function was preserved in the face of hyperlipidaemia. In 12 GSD III patients, one had a focal hepatic lesion and 6 had pronounced left ventricular hypertrophy, although cardiorespiratory function was normal. These data emphasize the multisystem nature of these disorders and highlight the need for careful longterm follow-up.

Osteoporosis in juvenile-onset diabetes mellitus: morphometric and comparative studies

Ribs and vertebrae of 8 children and young adults aged from 17 months to 24 years with juvenile-onset diabetes mellitus, 4 with diabetes secondary to cystic fibrosis and 2 with diabetes secondary to thalassemia major, were analyzed for osteoporosis by a point-count morphometric method. The mean ratio of bone spicule to marrow space in cancellous bone of ribs of patients with juvenile-onset diabetes mellitus or with diabetes mellitus secondary to cystic fibrosis or thalassemia was 55% that of 10 control patients. The lengths of the zones of proliferating and mature cartilage cells in costal epiphyses of patients with juvenile-onset diabetes mellitus were also below normal. The ratio of bone spicule to marrow space of vertebrae of the diabetic patients was not significantly different from control values. The data confirm clinical reports that osteoporosis is a regular feature of juvenile-onset diabetes mellitus and suggest that the degree of bone matrix and mineral deficiency in such patients is greater than is usually considered.