Late-onset muscular weakness in phosphofructokinase deficiency due to exon 5/intron 5 junction point mutation: a unique disorder or the natural course of this glycolytic disorder?

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.

Juvenile-onset permanent weakness in muscle phosphofructokinase deficiency

We describe a 41-year-old Moroccan woman with phosphofructokinase (PFK) deficiency who presented slowly progressive muscular weakness since childhood, without rhabdomyolysis episode or hemolytic anemia. Deltoid biopsy revealed massive glycogen storage in the majority of muscle fibers and polysaccharide deposits. PFK activity in muscle was totally absent. A novel homozygous non-sense mutation was detected in PFKM gene. Our observation suggests that juvenile-onset fixed muscle weakness may be a predominant clinical feature of PFK deficiency. Vacuolar myopathy with polyglucosan deposits remains an important morphological hallmark of this rare muscle glycogenosis.

Clinical features and new molecular findings in muscle phosphofructokinase deficiency (GSD type VII)

Muscle phosphofructokinase (PFKM) deficiency, a rare disorder of glycogen metabolism also known as glycogen storage disease type VII (GSDVII), is characterized by exercise intolerance, myalgias, cramps and episodic myoglobinuria associated with compensated hemolytic anaemia and hyperuricemia. We studied five patients with PFKM deficiency coming from different Italian regions. All probands showed exercise intolerance, hyperCKemia, cramps and myoglobinuria. One patient had a mild hypertrophic cardiomyopathy. Biochemical studies revealed residual PFK activity ranging from 1 to 5%. Molecular genetic analysis identified four novel mutations in the PFKM gene. In our series of patients, clinical and laboratory features were similar in all but one patient, who had an unusual phenotype characterized by 25 ears disease history, high CK levels, hypertrophic cardiomyopathy with paroxysmal atrial fibrillation without fixed muscle weakness.

Is it really myositis? A consideration of the differential diagnosis

PURPOSE OF REVIEW

The idiopathic inflammatory myopathies are an important and treatable group of disorders. However, the potential toxicity associated with the immune therapeutic regimens used to treat these disorders may be significant; therefore, accurate diagnosis before such treatment is essential. The differential diagnosis is potentially large. Accurate diagnosis usually depends on a combination of careful clinical assessment in conjunction with detailed laboratory investigations. Muscle biopsy remains essential in achieving an accurate diagnosis that will then guide treatment. This review describes the diagnostic approach used.

RECENT FINDINGS

There has been debate over the requirements for an accurate diagnosis of inflammatory myopathy (i.e., polymyositis and dermatomyositis). It is increasingly recognized that there can be clinical and muscle histopathologic overlap between the features of inflammatory myopathies and those of other muscle disorders, in particular, the genetic muscular dystrophies. Pathologic findings of inflammation and major histocompatibility complex upregulation, although typical of inflammatory myopathies, have been shown to occur in some muscular dystrophies, complicating the diagnostic process. Inclusion body myositis is much less responsive to immunotherapy and is now recognized as the most common acquired muscle disease in those older than 50 years of age. It is likely that genetic muscular dystrophies and inclusion body myositis account for some cases of apparently "treatment-resistant" myositis.

SUMMARY

A thorough clinical assessment, including a detailed family history, complemented by electromyography and creatine kinase measurements, should be undertaken in any patient with presumed idiopathic inflammatory myopathy. In addition, a muscle biopsy remains essential in all cases. A precise tissue diagnosis confirming features of an active inflammatory process should be achieved before immunosuppressive treatment is commenced. An increasing array of immunocytochemical and histioenzymatic stains now allows a full analysis and will help to confirm or exclude virtually all the differential diagnostic possibilities considered in this review. Electron microscopy may also be valuable in selected cases. Close collaboration between clinicians and muscle pathologists is essential in allowing the most accurate interpretation of myopathologic findings in the clinical context.

Glycogen storage myopathies

The glycogen storage myopathies are caused by enzyme defects in the glycogenolytic or in the glycolytic pathway affecting skeletal muscle alone or in conjunction with other tissues. The authors review recent findings in this area, including a new entity, aldolase deficiency, and the wealth of molecular genetic data that are rapidly accumulating. Despite this progress, genotype-phenotyp3 correlations are still murky in most glycogen storage myopathies.

Molecular basis of muscle phosphoglycerate mutase (PGAM-M) deficiency in the Italian kindred

Human muscle phosphoglycerate mutase (PGAM-M) deficiency is associated with exercise intolerance, muscle cramps, chronic serum CK elevation, and recurrent episodes of myoglobinuria. Ten patients have been described: 7 African Americans, 1 African, and 2 Caucasians from the Italian kindred described here. Molecular genetic analysis has revealed three different mutations in the PGAM-M gene. The propositus of the Italian family was homozygous for a unique point mutation at codon 90 in exon 1, a C-to-T transition converting an encoded arginine to tryptophan. His sister, who had similar complaints, was also homozygous for this mutation while the paternal grandfather, both parents, a brother and a nephew of the propositus were heterozygous for the mutation. Our studies exclude that PGAM-M deficiency is limited to African Americans, and suggest that the molecular heterogeneity of this rare disorder may be due to a "founder effect" in different ethnic groups.

Phosphofructokinase deficiency: recent advances in molecular biology

Phosphofructokinase (PFK) plays a major role in glycolysis. Deficiency of PFK-M is characterized by muscle weakness due to fuel crisis in exercising muscles. To elucidate the gene defect of PFK-deficient patients, we have cloned and determined the complete structure and transcription mechanism of human PFK-M mRNA and gene. Molecular defects were investigated in three unrelated Japanese family cases. The first case was characterized by a point mutation at the donor site of intron 15 of the PFK-M gene. Cryptic splicing resulted in a 25 amino acid truncation in the patient's PFK-M. The second case possessed a point mutation at the donor site of intron 19, resulting in the skipping of exon 19 and the truncation of 55 amino acids. In the third case, a missense mutation was identified in the coding region. The review of an updated mutation repertoire indicates the heterogeneity of the molecular mechanism of the disease.

A new variant case of muscle phosphofructokinase deficiency, coexisting with gastric ulcer, gouty arthritis, and increased hemolysis

Muscle phosphofructokinase (PFK) deficiency includes both clinically and genetically heterogeneous conditions. A 22-year-old man with muscle PFK deficiency due to previously unrecognized mutation was admitted because of gastric ulcer. He had noticed mild fatigability on vigorous exercise, but had never experienced painful cramps and myoglobinuria. His history included five time relapses of gastric ulcer and gouty arthritis at ages 19 and 21 years. His laboratory data showing impaired muscle glycolysis, increased hemolysis, and myogenic hyperuricemia had aspects in common with those reported for the classic form of this disease, except that lactate concentrations in his blood increased considerably after exercise. The mutant PFK enzyme of this patient, who was demonstrated to have a missense mutation, could exert some catalytic activity that permitted glycolytic flux in vivo, thus leading to the absence of typical myopathic symptoms. The association of relapsing gastric ulcer with muscle PFK deficiency was detected for the first time. There is a possibility that oxygen radical-induced tissue damage resulting from increased hypoxanthine on exertion plays a role in the pathogenesis of ulceration, since the patient is more tolerant to exercise than reported cases with the classic form of muscle PFK deficiency.

Mutations in muscle phosphofructokinase gene

Mutations in the muscle phosphofructokinase gene (PFK-M) result in a metabolic myopathy characterized by exercise intolerance and compensated hemolysis. PFK deficiency, glycogenosis type VII (Tarui disease) is a rare, autosomal, recessively inherited disorder. Multiple mutations, including splicing defects, frameshifts, and missense mutations, have recently been identified in patients from six different ethnic backgrounds establishing genetic heterogeneity of the disease. There is no obvious correlation between the genotype and phenotypic expression of the disease. PFK-M deficiency appears to be prevalent among people of Ashkenazi Jewish descent. Molecular diagnosis is now feasible for Ashkenazi patients who share two common mutations in the gene; the more frequent is an exon 5 splicing defect, which accounts for approximately 68% of mutant alleles in this population.