In the United States, 1 in 2,500 live births are afflicted with SCD ( 3), and it is estimated that 100,000 patients with SCD live in the United States ( 4). It is estimated that 300,000 infants are born annually with SCD, most in sub-Saharan Africa ( 1, 2). Patients with HbSS and HbSβ 0 experience severe symptoms, whereas patients with HbSC and HbSβ + are generally less affected. Patients who inherit the sickle β-chain mutation along with other distinct β-chain mutations such as sickle β-thalassemia (HbSβ 0 or HbSβ + thalassemia) or hemoglobin C (HbSC disease) also exhibit the SCD phenotype. Patients who are heterozygous at this locus have sickle cell trait (HbAS) and are largely asymptomatic, whereas patients homozygous for the sickle β-chain mutation have sickle cell anemia (HbSS). Hemoglobin that incorporates this amino acid substitution is referred to as sickle hemoglobin (HbS).
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The sickle cell disease (SCD) phenotype is the result of the substitution of valine for glutamine at the 6th amino acid position of the β-chain. Normal hemoglobin is composed of hemoglobin A (95% of total hemoglobin), which contains two α-chains and two beta (β)-chains, hemoglobin A2, which is composed of two α-chains and two delta (δ)-chains (1–4%), and fetal hemoglobin, which consists of two α-chains and two gamma (γ)-chains (70–90% at birth, with a subsequent decline through the first 6 months of life). Human hemoglobin is a tetramer comprising two alpha (α) and two non-α globin chains that envelop oxygen-carrying heme moieties. In this concise narrative review, we summarize the data that describes the importance of infectious diseases as a contributor to death and disability in SCD and discuss pathophysiology, prevalent organisms, prevention, management of acute episodes of critical illness, and ongoing care. All clinicians, regardless of their discipline, who assume the care of SCD patients must understand the importance of infectious disease as a contributor to death and disability. In contrast, in high-income countries, perinatal diagnosis of SCD, antimicrobial prophylaxis, vaccination, aggressive use of antibiotics for febrile episodes, and the availability of contemporary critical care resources have resulted in a significant reduction in deaths from infection however, chronic organ injury is problematic. Thus, the greatest gains in preventing infection-associated mortality can be achieved by addressing these factors for SCD patients in austere environments. Infection remains a main cause of overall mortality in patients with SCD in low- and middle-income countries due to increased exposure to pathogens, increased co-morbidities such as malnutrition, lower vaccination rates, and diminished access to definitive care, including antibiotics and blood. Vascular occlusion and increased blood viscosity results in functional asplenia and immune deficiency in early childhood, resulting in life-long increased susceptibility to serious bacterial infections. Sickle hemoglobin polymerizes in the deoxygenated state, resulting in erythrocyte membrane deformation, vascular occlusion, and hemolysis. Life-threatening acute physiologic crises may occur on a background of progressive diminishing vital organ function.
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Sickle cell disease (SCD) results in chronic hemolytic anemia, recurrent vascular occlusion, insidious vital organ deterioration, early mortality, and diminished quality of life.
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Vandy Black 2, Silvana Carr 3, Judy Lew 3, Kevin Sullivan 1,4 * and Niranjan Kissoon 5