Phosphoglycerate kinase deficiency in two brothers with McArdle-like clinical symptoms

A Mild Clinical Phenotype with Myopathic and Hemolytic Forms of Phosphoglycerate Kinase Deficiency (PGK Osaka): A Case Report and Literature Review

Phosphoglycerate kinase (PGK) deficiency is an X-linked disorder characterized by a combination of hemolytic anemia, myopathy, and brain involvement. We herein report a Japanese man who had several episodes of rhabdomyolysis but was training strenuously to be a professional boxer. Mild hemolytic anemia was noted. The enzymatic activity of PGK was significantly reduced, and a novel missense mutation, p.S62N, was identified in the PGK1 gene. A literature review revealed only one case with a mixed hemolytic and myopathic phenotype like ours. This mild phenotype indicates the complex pathophysiology of PGK deficiency and suggests the benefits of dietary control and exercise.

Non-traumatic and non-drug-induced rhabdomyolysis

Rhabdomyolysis (RM), a fortunately rare disease of the striated muscle cells, is a complication of non-traumatic (congenital (glycogen storage disease, discrete mitochondrial myopathies and various muscular dystrophies) or acquired (alcoholic myopathy, systemic diseases, arterial occlusion, viral illness or bacterial sepsis)) and traumatic conditions. Additionally, RM can occur in some individuals under specific circumstances such as toxic substance use and illicit drug abuse. Lipid-lowering drugs in particular are capable of causing RM. This comprehensive review will focus on non-traumatic and non-drug-induced RM. Moreover, the pathology of RM, its clinical manifestation and biochemical effects, and finally its management will be discussed.

A Novel Missense Variant Associated with A Splicing Defect in A Myopathic Form of PGK1 Deficiency in The Spanish Population

Phosphoglycerate kinase (PGK)1 deficiency is an X-linked inherited disease associated with different clinical presentations, sometimes as myopathic affectation without hemolytic anemia. We present a 40-year-old male with a mild psychomotor delay and mild mental retardation, who developed progressive exercise intolerance, cramps and sporadic episodes of rhabdomyolysis but no hematological features. A genetic study was carried out by a next-generation sequencing (NGS) panel of 32 genes associated with inherited metabolic myopathies. We identified a missense variant in the PGK1 gene c.1114G > A (p.Gly372Ser) located in the last nucleotide of exon 9. cDNA studies demonstrated abnormalities in mRNA splicing because this change abolishes the exon 9 donor site. This novel variant is the first variant associated with a myopathic form of PGK1 deficiency in the Spanish population.

Phosphoglycerate kinase deficiency: A nationwide multicenter retrospective study

Phosphoglycerate kinase (PGK) deficiency is a rare X-linked metabolic disorder caused by mutations in the PGK1 gene. Patients usually develop various combinations of nonspherocytic hemolytic anemia (NSHA), myopathy, and central nervous system disorders. In this national multicenter observational retrospective study, we recorded all known French patients with PGK deficiency, and 3 unrelated patients were identified. Case 1 was a 32-year-old patient with severe chronic axonal sensorimotor polyneuropathy resembling Charcot-Marie-Tooth (CMT) disease, mental retardation, microcephaly, ophthalmoplegia, pes cavus, and the new c.323G > A PGK1 hemizygous mutation. Case 2 was a 71-year-old patient with recurrent exertional rhabdomyolysis, and a c.943G > A PGK1 hemizygous mutation. Case 3 was a 48-year-old patient with NSHA, retinitis pigmentosa, mental retardation, seizures, stroke, parkinsonism, and a c.491A > T PGK1 hemizygous mutation. This study confirms that PGK deficiency is an extremely rare disorder with a wide phenotypic spectrum, and demonstrates for the first time that PGK deficiency may affect the peripheral nervous system and present as a CMT-like disorder.

Myopathies Related to Glycogen Metabolism Disorders

Most of the glycogen metabolism disorders that affect skeletal muscle involve enzymes in glycogenolysis (myophosphorylase (PYGM), glycogen debranching enzyme (AGL), phosphorylase b kinase (PHKB)) and glycolysis (phosphofructokinase (PFK), phosphoglycerate mutase (PGAM2), aldolase A (ALDOA), β-enolase (ENO3)); however, 3 involve glycogen synthesis (glycogenin-1 (GYG1), glycogen synthase (GSE), and branching enzyme (GBE1)). Many present with exercise-induced cramps and rhabdomyolysis with higher-intensity exercise (i.e., PYGM, PFK, PGAM2), yet others present with muscle atrophy and weakness (GYG1, AGL, GBE1). A failure of serum lactate to rise with exercise with an exaggerated ammonia response is a common, but not invariant, finding. The serum creatine kinase (CK) is often elevated in the myopathic forms and in PYGM deficiency, but can be normal and increase only with rhabdomyolysis (PGAM2, PFK, ENO3). Therapy for glycogen storage diseases that result in exercise-induced symptoms includes lifestyle adaptation and carefully titrated exercise. Immediate pre-exercise carbohydrate improves symptoms in the glycogenolytic defects (i.e., PYGM), but can exacerbate symptoms in glycolytic defects (i.e., PFK). Creatine monohydrate in low dose may provide a mild benefit in PYGM mutations.

Level of residual enzyme activity modulates the phenotype in phosphoglycerate kinase deficiency

OBJECTIVE

To study the variable clinical picture and exercise tolerance of patients with phosphoglycerate kinase (PGK) 1 deficiency and how it relates to residual PGK enzyme activity.

METHODS

In this case series study, we evaluated 7 boys and men from 5 families with PGK1 deficiency. Five had pure muscle symptoms, while 2 also had mild intellectual disability with or without anemia. Muscle glycolytic and oxidative capacities were evaluated by an ischemic forearm exercise test and by cycle ergometry.

RESULTS

Enzyme levels of PGK were 4% to 9% of normal in red cells and 5% to10% in muscle in pure myopathy patients and 2.6% in both muscle and red cells in the 2 patients with multisystem involvement. Patients with pure myopathy had greater increases in lactate with ischemic exercise (2-3 mmol/L) vs the 2 multisystem-affected patients (<1 mmol/L). Myopathy patients had higher oxidative capacity in cycle exercise vs multisystem affected patients (≈30 vs ≈15 mL/kg per minute). One multisystem-affected patient developed frank myoglobinuria after the short exercise test.

CONCLUSIONS

This case series study of PGK1 deficiency suggests that the level of impaired glycolysis in PGK deficiency is a major determinant of phenotype. Lower glycolytic capacity in PGK1 deficiency seems to result in multisystem involvement and increased susceptibility to exertional rhabdomyolysis.

Diagnostic evaluation of rhabdomyolysis

Rhabdomyolysis is characterized by severe acute muscle injury resulting in muscle pain, weakness, and/or swelling with release of myofiber contents into the bloodstream. Symptoms develop over hours to days after an inciting factor and may be associated with dark pigmentation of the urine. Serum creatine kinase and urine myoglobin levels are markedly elevated. Clinical examination, history, laboratory studies, muscle biopsy, and genetic testing are useful tools for diagnosis of rhabdomyolysis, and they can help differentiate acquired from inherited causes of rhabdomyolysis. Acquired causes include substance abuse, medication or toxic exposures, electrolyte abnormalities, endocrine disturbances, and autoimmune myopathies. Inherited predisposition to rhabdomyolysis can occur with disorders of glycogen metabolism, fatty acid β-oxidation, and mitochondrial oxidative phosphorylation. Less common inherited causes of rhabdomyolysis include structural myopathies, channelopathies, and sickle-cell disease. This review focuses on the differentiation of acquired and inherited causes of rhabdomyolysis and proposes a practical diagnostic algorithm. Muscle Nerve 51: 793-810, 2015.

Slow internal protein dynamics in solution

Large-scale domain dynamics in proteins are found when flexible linkers or hinges connect domains. The related conformational changes are often related to the function of the protein,for example by arranging the active center after substrate binding or allowing transport and release of products. The adaptation of a specific active structure is referred to as ‘induced fit’ and is challenged by models such as ‘conformational sampling’. Newer models about protein unction include some flexibility within the protein structure or even internal dynamics of the protein. As larger domains contribute to the configurational changes, the timescale of the involved motions is slowed down. The role of slow domain dynamics is being increasingly recognized as essential to understanding the function of proteins. Neutron spin echospectroscopy (NSE) is a technique that is able to access the related timescales from 0.1 up to several hundred nanoseconds and simultaneously covers the length scale relevant for protein domain movements of several nanometers distance between domains. Here we focus on these large-scale domain fluctuations and show how the structure and dynamics of proteins can be assessed by small-angle neutron scattering and NSE.

Protein Stability, Folding and Misfolding in Human PGK1 Deficiency

Conformational diseases are often caused by mutations, altering protein folding and stability in vivo. We review here our recent work on the effects of mutations on the human phosphoglycerate kinase 1 (hPGK1), with a particular focus on thermodynamics and kinetics of protein folding and misfolding. Expression analyses and in vitro biophysical studies indicate that disease-causing mutations enhance protein aggregation propensity. We found a strong correlation among protein aggregation propensity, thermodynamic stability, cooperativity and dynamics. Comparison of folding and unfolding properties with previous reports in PGKs from other species suggests that hPGK1 is very sensitive to mutations leading to enhance protein aggregation through changes in protein folding cooperativity and the structure of the relevant denaturation transition state for aggregation. Overall, we provide a mechanistic framework for protein misfolding of hPGK1, which is insightful to develop new therapeutic strategies aimed to target native state stability and foldability in hPGK1 deficient patients.

A new variant of phosphoglycerate kinase deficiency (p.I371K) with multiple tissue involvement: molecular and functional characterization

Phosphoglycerate kinase (PGK) is a key glycolytic enzyme that catalyzes the reversible phosphotransfer reaction from 1,3-bisphosphoglycerate to MgADP, to form 3-phosphoglycerate and MgATP. Two isozymes encoded by distinct genes are present in humans: PGK-1, located on Xq-13.3, encodes a ubiquitous protein of 417 amino acids, whereas PGK-2 is testis-specific. PGK1 deficiency is characterized by mild to severe hemolytic anemia, neurological dysfunctions and myopathy; patients rarely exhibit all three clinical features. Nearly 40 cases have been reported, 27 of them characterized at DNA or protein level, and 20 different mutations were described. Here we report the first Italian case of PGK deficiency characterized at a molecular and biochemical level. The patient presented during infancy with hemolytic anemia, increased CPK values, and respiratory distress; the study of red blood cell enzymes showed a drastic reduction in PGK activity. In adulthood he displayed mild hemolytic anemia, mental retardation and severe myopathy. PGK-1 gene sequencing revealed the new missense mutation c.1112T>A (p.Ile371Lys). The mutation was not found among 100 normal alleles, and even if located in the third to the last nucleotide of exon 9, it did not alter mRNA splicing. The p.Ile371Lys mutation falls in a conserved region of the enzyme, near the nucleotide binding site. The mutant enzyme shows reduced catalytic rates toward both substrates (apparent k(cat) values, 12-fold lower than wild-type) and a decreased affinity toward MgATP (apparent K(m), 6-fold higher than wild-type). Moreover, it lost half of activity after nearly 9-min incubation at 45°C, a temperature that did not affect the wild-type enzyme (t(1/2)>1 h). The possible compensatory expression of PGK2 isoenzyme was investigated in the proband and in the heterozygote healthy sisters, and found to be absent. Therefore, the highly perturbed catalytic properties of the new variant p.Ile371Lys, combined with protein instability, account for the PGK deficiency found in the patient and correlate with the clinical expression of the disease.

Molecular insights on pathogenic effects of mutations causing phosphoglycerate kinase deficiency

Phosphoglycerate kinase (PGK) catalyzes an important ATP-generating step in glycolysis. PGK1 deficiency is an uncommon X-linked inherited disorder, generally characterized by various combinations of non-spherocytic hemolytic anemia, neurological dysfunctions, and myopathies. Patients rarely exhibit all three clinical features. To provide a molecular framework to the different pathological manifestations, all known mutations were reviewed and 16 mutant enzymes, obtained as recombinant forms, were functionally and structurally characterized. Most mutations heavily affect thermal stability and to a different extent catalytic efficiency, in line with the remarkably low PGK activity clinically observed in the patients. Mutations grossly impairing protein stability, but moderately affecting kinetic properties (p.I47N, p.L89P, p.C316R, p.S320N, and p.A354P) present the most homogeneous correlation with the clinical phenotype. Patients carrying these mutations display hemolytic anemia and neurological disorders, and,except for p.A354P variant, no myopaty. Variants highly perturbed in both catalytic efficiency (p.G158V, p.D164V, p.K191del, D285V, p.D315N, and p.T378P) and heat stability (all, but p.T378P) result to be mainly associated with myopathy alone. Finally, mutations faintly affecting molecular properties (p.R206P, p.E252A, p.I253T, p.V266M, and p.D268N) correlate with a wide spectrum of clinical symptoms. These are the first studies that correlate the clinical symptoms with the molecular properties of the mutant enzymes. All findings indicate that the different clinical manifestations associated with PGK1 deficiency chiefly depend on the distinctive type of perturbations caused by mutations in the PGK1 gene, highlighting the need for determination of the molecular properties of PGK variants to assist in prognosis and genetic counseling. However, the clinical symptoms can not be understood only on the bases of molecular properties of the mutant enzyme. Different (environmental, metabolic, genetic and/or epigenetic) intervening factors can contribute toward the expression of PGK deficient clinical phenotypes.

Myopathic form of phosphoglycerate kinase (PGK) deficiency: a new case and pathogenic considerations

We describe an 18-year-old man with muscle cramps and recurrent exertional myoglobinuria, without hemolytic anemia or brain dysfunction. Phosphoglycerate kinase (PGK) deficiency was documented in muscle and erythrocytes and molecular analysis of the PGK1 gene identified a novel mutation, T378P. This is the ninth case presenting with isolated myopathy, whereas most other patients show hereditary non-spherocytic hemolytic anemia alone or associated with brain dysfunction, and a few patients have myopathy plus brain involvement. Although the diverse tissue involvement in PGK deficiency remains unclear, all mutations in myopathic patients tend to cluster in the C terminal domain, adjacent to the substrate-binding pocket. This may lead to a failure in the closure of the N terminal and C terminal domains and loss of stability due to lack of inter-domain communication during the catalytic process.

Altered expression ofPGK1in a family with phosphoglycerate kinase deficiency

The X-linked recessive disease phosphoglycerate kinase (PGK) deficiency is caused by altered expression of the PGK1 enzyme, which causes muscle stiffness, hemolytic anemia, and mental retardation. In this study we characterized the PGK1 gene in a family of two brothers, two sisters, and their parents. A single mutation in exon 6, which was associated with the pattern of inheritance of PGK1 deficiency, was observed. This silent G213G; c.639C>T mutation was localized to the conserved exon-intron boundary. We have developed a method for quantification of PGK1 mRNA and demonstrated a marked reduction in PGK1 mRNA in both brothers with the disease. A smaller decrease in PGK1 expression was observed in one sister with symptoms of PGK deficiency and in her mother. Only the normal PGK1 allele was expressed in the two heterozygous women. Whereas most known PGK1 mutations cause amino acid alterations, our study indicates that inhibition of the transcription mechanism is the cause of PGK deficiency.

A novel missense mutation (1060G --> C) in the phosphoglycerate kinase gene in a Japanese boy with chronic haemolytic anaemia, developmental delay and rhabdomyolysis

We report the case of a 3-year-old Japanese boy with phosphoglycerate kinase 1 (PGK1) deficiency (Online Mendelian Inheritance in Man entry 311800). The patient had anaemia and jaundice at birth, necessitating exchange transfusions for 2 d. After one red blood cell transfusion at age 2 months, his Hb level was 8-9 g/dl, his reticulocyte counts were 300-500 x 109/l, and his total bilirubin level was 25.65-42.75 micro mol/l. The patient suffered two episodes of respiratory infection-associated haemolytic crisis and rhabdomyolysis during early infancy. At age 3.0 years, his developmental milestones (developmental quotients measured using the Tsumori-Inage methods) score was 49% (normal 74-131%), and his height was below average by -2.0 standard deviations. The diagnosis of PGK1 deficiency was made based on his remarkably low (< 10% of normal) erythrocyte PGK enzyme activity level and the identification of a novel missense (1060G-->C) PGK1 gene mutation. This mutation results in the Ala-353Pro amino acid substitution, which has been designated PGK Kyoto. The patient developed the full clinical symptoms of PGK1 deficiency including haemolytic anaemia, myopathy, central nervous system disorder and growth retardation, which is unusual.

A nonischemic forearm exercise test for McArdle disease

Ischemic forearm exercise invariably causes muscle cramps and pain in patients with glycolytic defects. We investigated an alternative diagnostic exercise test that may be better tolerated. Nine patients with McArdle disease, one with the partial glycolytic defect phosphoglycerate mutase deficiency, and nine matched, healthy subjects performed the classic ischemic forearm protocol and an identical protocol without ischemia. Blood was sampled in the median cubital vein of the exercised arm. Plasma lactate level increased similarly in healthy subjects during ischemic (Delta5.1 +/- 0.7mmol L(-1)) and non-ischemic (Delta4.4 +/- 0.3) tests and decreased similarly in McArdle patients (Delta-0.10 +/- 0.02 vs Delta-0.40 +/- 0.10mmol L(-1)). Postexercise peak lactate to ammonia ratios clearly separated patients and healthy controls in ischemic (McArdle, 4 +/- 2 [range, 1-12]; partial glycolytic defect phosphoglycerate mutase deficiency, 6; healthy, 33 +/- 4 [range, 17-56]) and non-ischemic (McArdle, 5 +/- 1 [range, 1-10]; partial glycolytic defect phosphoglycerate mutase deficiency, 5; healthy, 42 +/- 3 [range, 35-56]) protocols. Similar differences in lactate to ammonia ratio between patients and healthy subjects were observed in two other work protocols using intermittent handgrip contraction at 50% and static handgrip exercise at 30% of maximal voluntary contraction force. All patients developed pain and cramps during the ischemic test, and four had to abort the test prematurely. No patient experienced cramps in the non-ischemic test, and all completed the test. The findings indicate that the diagnostic ischemic forearm test for glycolytic disorders should be replaced by an aerobic forearm test.