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690 Part VI: The Erythrocyte Chapter 47: Erythrocyte Enzyme Disorders 691

National allele freq.
0-1%
>1-3%
>3-7%
>7-10%
>10-13%
>13-17%
>17-20%
>20-23%
Malaria free
A

G6PDd males (1,000s)
<50
50-100
100-500
500-1,000
1,000-2,500
2,500-5,000
5,000-10,000
>10,000
Malaria free
B

Figure 47–1. Estimated prevalence of glucose-6-phosphate dehydrogenase (G6PD) deficiency. A. National-level allele frequencies. B. National-level
population estimates of G6PD-deficient (G6PDd) males. (Reproduced with permission from Howes RE, Piel FB, Patil AP, et al: G6PD deficiency prevalence and
estimates of affected populations in malaria endemic countries: a geostatistical model-based map. PLoS Med 2012;9(11):e1001339.)

ETIOLOGY AND PATHOGENESIS high concentrations of oxygen within the erythrocyte and would then
be unable to perform its function of transporting oxygen and carbon
RED CELL METABOLISM dioxide.
The process of extracting energy from a substrate, such as glucose,
Although the binding, transport, and delivery of oxygen do not require and of utilizing this energy is carried out by a large number of enzymes
the expenditure of metabolic energy by the red cell, a source of energy (Table 47–1). Because the red cell loses its nucleus before it enters the
is required if the red cell is to perform its function efficiently and to circulation and most of its RNA within 1 or 2 days of its release into
survive in the circulation for its full life span of approximately 120 days. the circulation, it does not have the capacity to synthesize new proteins
This energy is needed to maintain (1) the iron of hemoglobin in the to replace those that may become degraded during its life span. The
divalent form; (2) the high potassium and low calcium and sodium lev- enzymes present in the red cells were formed largely by the nucleated
els within the cell against a gradient imposed by the high plasma cal- cell in the marrow and, to a lesser extent, the reticulocyte.
cium and sodium and low plasma potassium levels; (3) the sulfhydryl
groups of red cell enzymes, hemoglobin, and membranes in the active,
reduced form; and (4) the biconcave shape of the cell. If the red cell is Glucose Metabolism
deprived of a source of energy, it becomes sodium and calcium logged Glucose is the normal energy source of the red cell. It is metabolized by
and potassium depleted, and the red cell shape changes from a flexible the erythrocyte along two major routes: the glycolytic pathway and the
biconcave disk. Such a cell is quickly removed from the circulation by hexose monophosphate shunt. The steps in these pathways are essen-
the filtering action of the spleen and the monocyte–macrophage sys- tially the same as those found in other tissues and in other organisms,
tem. Even if it survived, such an energy-deprived cell would gradually including even relatively simple ones such as Escherichia coli and yeast.
turn brown as hemoglobin is oxidized to methemoglobin by the very Unlike most other cells, however, the red cell lacks mitochondria and

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