Introduction
Sickle cell disease (SCD) is the most common genetic disorder present in the United States, with about 1 in 13 African Americans being born with sickle cell trait and approximately 100,000 individuals currently living with disease. The state of Mississippi has the highest incidence rate of SCD in the United States(1). SCD is a life-limiting genetic condition that results in acute vaso-occlusive pain episodes, organ damage, stroke, and cardiovascular disease (2, 3).(5) Due to the chronic hemolysis [lysing of red blood cells (RBCs)] that occurs with sickle cell disease, patients with SCD have traditionally had a high basal metabolic rate and increased energy consumption (measured by resting energy expenditure) resulting from rapid production of new RBCs(3). Therefore, SCD has historically been characterized by poor growth, short stature, and patients being underweight to normal weight.
More recently, a retrospective chart review from 6 institutions in New England reported nearly one-quarter of children and adolescents with SCD are overweight or obese(4). This study found that the primary risk factor for children and adolescents with SCD being overweight/obese was increased baseline Hemoglobin levels (Hb), with a 36% increased odds of being overweight/obese for each 1g/dL increase in baseline Hb. One possible explanation for this shift in weight status for children and adolescents with SCD is improved medical management. For instance, the use of chronic transfusion therapy and hydroxyurea medication have both been shown to increase children’s z-scores for height, weight and BMI over 24 months compared to those children not on treatment(5, 6). These treatments increase hemoglobin level, reduce RBC turnover and reticulocytosis, and is thought to reduce the metabolic state and increased energy consumption that occurs in untreated SCD allowing for an increase in BMI.
Morbidity and mortality in SCD historically has been high due to complications of chronic hemolytic anemia, vaso-occlusion and impaired immune function. The mortality rate for children with SCD has improved in recent years due to comprehensive care, infection prophylaxis with penicillin and vaccination and the use of transcranial Doppler (TCD) to screen for stroke risk(7). As treatment continues to improve and mortality continues to decrease, an increase in BMI in SCD may emerge as a new risk factor for morbidity in this population. The consequences of overweight and obesity in children with SCD is currently unknown although it is thought to exacerbate comorbid conditions including obstructive sleep apnea, asthma and avascular necrosis(8). Systemic hypertension is an obesity-related complication which, has been associated with increased risk of stroke and death in patients with SCD(9). Adult studies have also demonstrated an increasing trend in BMI and a similar burden of type II diabetes among adult patients with SCD compared to African Americans without SCD. Specifically, adult patients with SCD have higher incidence of nephropathy, neuropathy and stroke(10).
The primary purpose of this study was to determine the prevalence of overweight and obesity in a pediatric population with SCD in Mississippi, compared to state and national rates of overweight and obesity. We hypothesized that rates of obesity in children with SCD in Mississippi would be similar to state and national rates. We further examined demographic (age, gender, insurance as proxy for socioeconomic status), baseline disease (genotype, hemoglobin level, hematocrit, absolute reticulocyte count), disease complications (acute chest syndrome, stroke, avascular necrosis), and treatment variables (hydroxyurea, chronic transfusion) as predictors of overweight/obesity in this sample.