Glutamic Pyruvate Transaminase Phenotypes in Polycythaemia Rubra Vera

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Abstract
Glutamate pyruvate transaminase (GPT) was studied in the red cells of 46 patients with a confirmed diagnosis of polycythemia rubra vera (PRV). The red cells of many of the patients showed low levels of enzyme activity. This activity could be restored by in vitro incubation with pyridoxal phosphate, suggesting that the effect was due to low levels of [vitamin] B6 rather than to a primary abnormality of the GPT. Patients with the lowest levels of GPT activity were likely to have clonal chromosomal abnormalities in the bone marrow cells, particularly 20q-. Among 43 patients in whom the GPT phenotypes were determined by electrophoresis, there was a marked deficiency of heterozygotes. This disturbance in phenotypic expression may be related to the clonal nature of the disease in PRV, the clone showing a lack of response to homeostatic controls and irregularities of gene expression.