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.