Hemoglobin C has a substitution of lysine for glutamic acid (a2P2glu^lys) in the sixth position of the N-terminal end of the beta chain. If hemoglobin C is inherited homozygously, the individual has hemoglobin C disease; if heterozygously, then hemoglobin C trait. Hemoglobin C disease has milder clinical symptoms than sickle cell anemia and has a much lower prevalence in the African American population (only 2% to 3%). In northern Ghana, however, the incidence of this particular hemoglobin is 17% to 28%.2 The anemia is normochromic and normocytic, yet there is some increase in the MCHC because red cells from homozygous individuals are denser. Most homozygous individuals show a moderate anemia with a hemoglobin value of between 9 and 12 g/dL. There is a moderate reticulocytosis and splenomegaly. The red cell life span is 38 days, yet few patients exhibit any symptoms. Of particular interest is the possible presence of crystalline structures in the red cells that appear as blocks or "bars of gold" (Fig. 8.7). These peculiar crystals obstruct the microvasculature but melt in the splenic microenvironment. Consequently, splenic function is preserved and little pitting occurs. Target cells (50% to 90%) are the predominant
Sickle Cell Trait
Sickle cell trait is achieved through heterozygous inheritance of hemoglobin S, in which an individual pos-
cell trait is 8% to 10% in the African American popula- f tion. Approximately 2.5 million people in the United | TeXt/ilTiage lights not available. States carry the sickle gene.27 Population penetrance in = parts of western Africa are as high as 25% to 30%, and §|
Several circumstances may put a sickle cell trait individ- s J ual in jeopardy of having a crisis episode, such as air ® £
travel in an unpressurized cabin and high altitudes. FigUre 8.7 Hemoglobin CC. Note the presence of crystals Other than this, sickle trait individuals lead normal shaped like "bars of gold" and many target cells.
red cell morphology, and variations of targeting may include folded or "pocketbook"-shaped cells. Sphero-cytes may be present. Alkaline electrophoresis will show a single slow moving band in the same position as hemoglobin A2.
The heterozygous condition is termed hemoglobin A-C trait, with a ratio of 60% hemoglobin A and 40% hemoglobin C on alkaline electrophoresis. There are no clinical complications for individuals with this condition, and they may never be noticed except for the presence of 40% target cells on their peripheral smear, an extremely abnormal finding (see Fig. 3.16). Individuals who inherit hemoglobin C should be aware of their hemoglobin status and that of prospective mates.
Hemoglobin SC disease is a combination of two abnormal hemoglobins, hemoglobin S and hemoglobin C. Affected individuals have a moderate anemia, with an average hemoglobin of 8 to 10 g/dL, with a slight reticu-locytosis. Red cell life span is reduced to approximately 29 days. Although the disease is less severe than sickle cell anemia, an individual may experience a painful crisis. Pregnant individuals may be severely affected. The peripheral smear shows high numbers of target cells; few reversible sickled cells, and folded cells, with a peculiar crystal shaped like the Washington Monument or a gloved hand showing in some cells (Fig. 8.8). The hemoglobin distribution on alkaline electrophoresis is 50% hemoglobin S and 50% hemoglobin C.
Was this article helpful?