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Sickle Cell Trait And Other Hemoglobinopathies

Sickle Cell Trait

Nearly 2 million people in the United States have sickle cell trait (SCT).13 SCT has little impact on overall morbidity and mortality, and patients who have it do not develop pain crises.13 The most significant conditions include hematuria and hyposthenuria (inability to concentrate urine). While hematuria occurs more frequently in SCT patients compared to the general population, it is sufficiently rare that when it occurs, another cause should always be sought.13 Hyposthenuria may lead to dehydration but is otherwise not clinically significant. The hypoxia of altitude exposure, as occurs with flights in un-pressurized airplanes, may result intravascular sickling.13

Hemoglobin SC Disease

HbC is a structural variant in which the normal glutamic acid at position 6 of the beta chain is replaced by lysine. When combined with the HbS gene, it is known as HbSC disease.1 This condition is found in one out of 833 people of African descent.6 Because the presence of HbC accentuates the deleterious effects of HbS, this makes HbSC disease a clinically significant disorder.6 Red blood cell indices typically demonstrate a microcytic and hyperchromic picture.14 When viewed under the microscope, these abnormal hemoglobins cause the red cells to fold over (resembling a taco).

All of the complications seen in SCD occur in patients with HbSC disease. Most of these complications are less frequent, less severe, and occur later in life when compared to SCA. The one exception is proliferative retinopathy, which is more common in those with HbSC disease.6

 Thalassemias

Thalassemia refers to a group of conditions that result from a deficiency in the production of the alpha globin chain (alpha thalassemia) or beta globin chain (beta thalassemia). Several syndromes exist, with varying clinical severities. The superscript 0 indicates that no globin chains are produced, while the superscript + indicates that globin chains are produced, but at a reduced rate.1

The imbalance caused by decreased production of the affected chain leads to insoluble, nonfunctioning chains that precipitate in the red cell membrane. This causes severe, ineffective erythropoiesis, characterized by low reticulocyte count and marked bone marrow expansion. This bone marrow expansion causes hepatosplenomegaly, pathologic fractures, bone deformities, and paraspinal masses.

Beta thalassemia (also known as thalassemia major or Cooley's anemia) usually presents during the first year of life. These patients require chronic transfusion therapy to survive. Their life is complicated by growth failure, severe anemia, infections, endocrine dysfunction, and early death, most commonly due to cardiac disease.15 Alpha thalassemia presents with chronic hemolytic anemia and all of the associated complications. The diagnosis and treatment of complications of the thalassemia syndromes are complex and should involve the patient's hematologist early in the course.

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Last Modified: 07/23/2017
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