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Morbidity & Mortality

Patients with SCA/SCD exhibit an array of clinical syndromes[17,27,38]. Many patients experience frequent bouts of debilitating painful episodes[31]. SCD is associated with significant morbidity and mortality[31]. These painful crises entail frequent and extended hospitalization periods[39]. As a result, many have a generally poor quality of life. Still, while some patients can incur fatal episodes in early childhood or adolescence, with the advent of better treatment and/or therapies, many more individuals do survive to adulthood.

SCD Morbidity

A number of well-defined sickling syndromes have been described that involve general patterns of expression in children and adults and/or specific tissue and damage to organ systems. The episodic painful vaso-occlusive crisis is the leading cause of SCD morbidity for all patients[27]. Young SCD patients display splenomegaly (splenic sequestration)[40]. Adolescents with SCD typically suffer from skin lesions and bone infarcts due to RBC trapping[28,29]. Cerebrovascular accidents (CVAs) occur in children and adolescents due to ischemia or hypoxia and result in significant neuropsychological impairment[41]. Many adults with the disease suffer from chronic tissue and major organ damage presumably due to obstruction by sickled cells, which accounts for most of the SCD-related deaths[42].

SCD Mortality 

Individuals with SCD are at increased risk of death at all stages of life. During infancy, without prophylactic intervention, infection is the primary cause of SCD death[43-45]. Young  children tend to lose splenic function due to infarction[45], which is a major cause of febrile (infectious) crises. The acute chest syndrome (ACS) is the major cause of death in adolescents[44]. Pulmonary infection resulting from trapping of sickled cells in the lung plays a major role in ACS[44]. Fatal CVAs occur in ~8% of children[44]. Conversely, the major cause (~33%) of death in adults is attributed to acute crises (painful vaso-occlusive episode(VOE)s  and ACS)[44]. Many of these latter ACS cases result from loss of pulmonary functioning due to infarcts and include heart failure due to myocardial ischemia[44]. In ~18% of adults organ (kidney) failure is the cause of death[44]. As a consequence of these abnormalities, the mean lifespan of treated SCD patients is markedly reduced[31,44],with the actual lifespan of the patient varying according to the degree of severity of anemia, organ damage and sickle cell-related complications.

Major Risk Factors

The major risk factor for early SCD fatality is a high intracellular level of Hb S (and low level of HbF) in RBCs[44]. Besides the cellular Hb S level, other important factors or variables include the frequency of VOEs, and presence of renal insufficiency, ACS, CVAs, and/or high white blood cell (WBC) counts[43,44].