Phosphoglycerate kinase San Francisco: a new variant associated with hemolytic anemia but not with neuromuscular manifestations

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.

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.

Biochemical and genetic basis of red cell enzyme deficiencies

Enzyme deficiencies have been identified in all erythrocyte pathways. Their frequencies differ with respect to the affected enzyme, the severity of the clinical manifestations and the geographical distribution. Most mutations are found within the coding sequences of genes, missense mutations occurring more often than deletions, insertions, splice site defects or premature stop codons. Promoter mutations are rare. The clinical manifestations are chronic or non-chronic haemolytic anaemias. The first of these are characterized by an impairment of cell function at normal values of the external load parameters kATPase and kGSHox. Haemolysis with a non-chronic course is induced only at enhanced values of the load parameters, caused by free radical generation by oxidative drugs, fava beans, infections, fever and physical exercise. The development of secondary haemochromatosis is the most common cause of mortality in patients suffering from severe chronic non-spherocytic haemolytic anaemia. Intracellular iron deposits must be prevented by timely treatment with effective chelating agents.

Hereditary red cell enzymopathies

The hereditary red cell enzymopathies are an uncommon but important cause of chronic haemolytic anaemia. Their clinical diversity is mirrored by increasingly evident heterogeneity at the molecular level. The structure, function, and expression of the genes encoding red cell enzymes and the nature of the gene defects in the deficient state are examined.

Molecular genetic heterogeneity of phosphoglycerate kinase (PGK) deficiency

Phosphoglycerate kinase (PGK; EC 2.7.2.3) is a glycolytic enzyme encoded by a single gene on the X chromosome and ubiquitously expressed. Hereditary PGK deficiency can cause hemolytic anemia, central nervous system dysfunction, and/or myopathy characterized by exercise intolerance, cramps, and myoglobinuria. So far, 20 PGK variants with reduced PGK activity have been identified, 8 of them in patients with myopathy. Six missense mutations and one splice-junction mutation have been identified in 7 patients, 2 of whom had myopathy. However, the biochemical and molecular bases for clinical heterogeneity in PGK deficiency remain unknown.

Recent progress in the molecular genetic analysis of erythroenzymopathy

During the relatively recent period in which normal genes for most red cell enzymes have been isolated, the techniques of molecular biology have been applied to the studies of erythroenzymopathy. Single nucleotide substitutions have been identified in aldolase, triosephosphate isomerase, glucose 6-phosphate dehydrogenase, and adenylate kinase variants by the cloning and nucleotide sequence of the patients' genes. Up to now, all of the enzyme-deficient variants which have been investigated have been caused by point mutations. An exception is a hemolytic anemia secondary to increased adenosine deaminase (ADA) activity. Red cell ADA activity increases on the order of a hundred-fold in affected individuals. The basic abnormality appears to result from overproduction of structurally normal enzyme due to abnormal transcriptional or translational efficiency.