Glycogen storage disease type IV without detectable polyglucosan bodies: importance of broad gene panels

Glycogen storage disease type IV (GSD IV) is caused by mutations in the glycogen branching enzyme 1 (GBE1) gene and is characterized by accumulation of polyglucosan bodies in liver, muscle and other tissues. We report three cases with neuromuscular forms of GSD IV, none of whom had polyglucosan bodies on muscle biopsy. The first case had no neonatal problems and presented with delayed walking. The other cases presented at birth: one with arthrogryposis, hypotonia, and respiratory distress, the other with talipes and feeding problems. All developed a similar pattern of axial weakness, proximal upper limb weakness and scapular winging, and much milder proximal lower limb weakness. Our cases expand the phenotypic spectrum of neuromuscular GSD IV, highlight that congenital myopathy and limb girdle weakness can be caused by mutations in GBE1, and emphasize that GSD IV should be considered even in the absence of characteristic polyglucosan bodies on muscle biopsy.

Energy metabolism during exercise in patients with β-enolase deficiency (GSDXIII)

AIM

To investigate the in vivo skeletal muscle metabolism in patients with β-enolase deficiency (GSDXIII) during exercise, and the effect of glucose infusion.

METHODS

Three patients with GSDXIII and 10 healthy controls performed a nonischemic handgrip test as well as an incremental cycle ergometer test measuring maximal oxidative consumption (VO2max) and a 1-hour submaximal cycle test at an intensity of 65% to 75% of VO2max. The patients repeated the submaximal exercise after 2 days, where they received a 10% iv-glucose supplementation.

RESULTS

Patients had lower VO2max than healthy controls, and two of three patients had to stop prematurely during the intended 1-hour submaximal exercise test. During nonischemic forearm test, all patients were able to produce lactate in normal amounts. Glucose infusion had no effect on patients' exercise capacity.

CONCLUSIONS

Patients with GSDXIII experience exercise intolerance and episodes of myoglobinuria, even to the point of needing renal dialysis, but still retain an almost normal anaerobic metabolic response to submaximal intensity exercise. In accordance with this, glucose supplementation did not improve exercise capacity. The findings show that GSDXIII, although causing episodic rhabdomyolysis, is one of the mildest metabolic myopathies affecting glycolysis.

Results of an open label feasibility study of sodium valproate in people with McArdle disease

McArdle disease results from a lack of muscle glycogen phosphorylase in skeletal muscle tissue. Regenerating skeletal muscle fibres can express the brain glycogen phosphorylase isoenzyme. Stimulating expression of this enzyme could be a therapeutic strategy. Animal model studies indicate that sodium valproate (VPA) can increase expression of phosphorylase in skeletal muscle affected with McArdle disease. This study was designed to assess whether VPA can modify expression of brain phosphorylase isoenzyme in people with McArdle disease. This phase II, open label, feasibility pilot study to assess efficacy of six months treatment with VPA (20 mg/kg/day) included 16 people with McArdle disease. Primary outcome assessed changes in VO₂peak during an incremental cycle test. Secondary outcomes included: phosphorylase enzyme expression in post-treatment muscle biopsy, total distance walked in 12 min, plasma lactate change (forearm exercise test) and quality of life (SF36). Safety parameters. 14 participants completed the trial, VPA treatment was well tolerated; weight gain was the most frequently reported drug-related adverse event. There was no clinically meaningful change in any of the primary or secondary outcome measures including: VO₂peak, 12 min walk test and muscle biopsy to look for a change in the number of phosphorylase positive fibres between baseline and 6 months of treatment. Although this was a small open label feasibility study, it suggests that a larger randomised controlled study of VPA, may not be worthwhile.

The need for biochemical testing in beta-enolase deficiency in the genomic era

Glycogen storage disease type XIII (GSDXIII) is a very rare inherited metabolic myopathy characterized by autosomal-recessive mutations in the ENO3 gene resulting in muscle β-enolase deficiency, an enzymatic defect of the distal part of glycolysis. Enzyme kinetic studies of two patients presenting with exertion intolerance and recurrent rhabdomyolysis are reported. Next generation sequencing confirmed patient 1 was homozygous for p.E187K in ENO3, while patient 2 was homozygous for p.C357Y. ENO3 variants pathogenicity was confirmed by functional studies in skeletal muscle. p.E187K caused extremely low total enolase activity. p.C357Y was associated with a higher level of residual activity but kinetic studies showed a lower maximum work rate (V max). This study illustrates that GSDXIII may be caused by either null mutations leading to β-enolase deficiency or by mutations that alter the enzyme's kinetic profile. This study highlights the importance of carrying out functional studies as part of the diagnostic process following the identification of variants with next generation sequencing.

[Rheumatic diseases in China]

To determine the prevalence of rheumatic diseases in Chinese of Han nationality in the north and the south of China, samples of 4,192 adults in Beijing (north) and 5,057 in Shantou (south) area were studied. The same questionnaire was administered to each subject surveyed. Physical examinations were done in all who gave positive answers. For those who gave positive response to certain set of questions, blood antinuclear antibody and rheumatoid factor tests and radiographs of hand and/or sacroiliac joint were done. The prevalence of definite rheumatoid arthritis (RA) was 0.34% in the north (95% confidence interval 0.20-0.51) and 0.32% (0.95% CI 0.16-0.47) in the south and ankylosing spondilitis was noted in 0.26% of both samples (95% confidence interval in the north 0.11-0.42 and in the south 0.14-0.40). Only 3 cases of systemic lupus erythematosus in the north and one in the south were identified. General rheumatic pain was reported more frequently in the north. Lumbar problems were recorded on examinations 5 times more commonly in the north than in the south (men 25.0% vs 5.3%, women 38.0% vs 6.5%) and knee problems 10 times (men 24.0% vs 1.8%, women 36.0% vs 3.4%) more commonly in the north; the difference was greatest in the age of 55-64. A further study in the south is planned to assess the contribution of inter-observer error and/or difference in cultural response to the north/south difference observed in the prevalence of general rheumatic symptoms and back pain. A search for environmental risk factors such as climate, diet, degeneration or overuse would then be indicated to explain these differences.

Rheumatic disease in a Philippine village. II: a WHO-ILAR-APLAR COPCORD study, phases II and III

Many difficulties were encountered in a population survey of rheumatic complaints in a remote village area in the Philippines affecting the reliability of estimates of population prevalence. In phase I, a simple questionnaire identified 269 adults out of 950 who had rheumatic symptoms. In Phase II, 234 or 87% of positive respondents were requestioned using a more detailed pro forma. There were 196 with peripheral joint pain, 67 with neck pain and 137 with back pain. One third attributed their symptoms to work and 127 subjects had to stop work because of their complaints. Disability, including an inability to carry loads, affected nearly 1.8% of the population. Questions designed to detect rheumatoid arthritis and gout were not satisfactorily answered. Of those with complaints, 82% indicated that they still required help for their symptoms. In phase III, 166 subjects were medically examined. Osteoarthritis of the knee was found in 25 and 17 had Heberden's nodes. There were 16 with epicondylitis; 16 had rotator cuff pain and 35 had levator scapulae insertion pain. Three of these and three others had neck or shoulder swellings related to carrying loads on poles. Definite rheumatoid arthritis was diagnosed in two subjects and gout in five. No case of ankylosing spondylitis was identified. Thus, rheumatic complaints were common in this rural community and were frequently severe enough to cause disability and loss of time from work. Health worker education is required on how to handle these problems.

Sustained release indomethacin: a double blind comparison with indomethacin suppositories

A double-blind crossover comparison of sustained release indomethacin capsules and indomethacin suppositories showed no efficacy advantage to either preparation. In other respects the two preparations were found to be comparable. More patients preferred the convenience of the oral route of medication when given the choice after the study was concluded.

Aspirin, phenacetin, and the kidney: a rheumatism clinic study

In a rheumatism clinic study in Brisbane, the consumption of aspirin and phenacetin compounds (APC) containing more than one kilogram of aspirin and phenacetin was significantly associated with overt renal papillary necrosis (RPN) and with a renal score, but when more than one kilogram of aspirin was taken without phenacetin there was no such association. Analysis and comparison with the parallel New Zealand study showed an overall risk of RPN of at least 10-6% when more than one kilogram of aspirin was taken in APC form, and 0-3% when aspirin was taken without phenacetin. An additive interaction of phenacetin and aspirin is postulated. It is concluded that phenacetin use should be severely restricted.