Prevalence of High Body Mass Index in Children with Sickle Cell Disease and Its Correlation of Disease Severity

Background

Children with sickle cell disease (SCD), particularly those with the homozygous form designated HbSS, have frequently been reported to suffer from impaired growth, delayed onset of puberty and poor nutritional status (1). However, improvement in healthcare of children with SCD in more economically developed countries, along with increased use of SCD-directed therapies such as hydroxyurea and chronic transfusions along with the recent rise in childhood obesity rates may have influenced growth of children with SCD. Two recent reports in the US found that 19-22% of children with SCD were overweight or obese (2, 3) . It is not known whether high body mass index (BMI) in children with SCD results in a worse clinical phenotype. Known association of childhood obesity with obstructive sleep apnoea (OSA) raises the potential of worsening clinical phenotype of SCD by increasing the incidence of nocturnal hypoxaemia which in turn may give rise to increased vaso-occlusive episodes (4). This study aimed to determine the prevalence of high body mass index (BMI) in an urban population of children in the UK with SCD and assess if there is correlation between BMI and disease severity.

Methods

A retrospective chart review was performed on all patients aged 2-18 years with SCD who attended an outpatient clinic at Kings College Hospital, London between April 2015 and April 2017. Acute sickle cell-related emergency department (ED) attendances and hospital admissions in this period were recorded. BMI percentile, demographic information and laboratory markers of disease were recorded from the most recent clinic visit. Age and gender specific definitions of BMI percentiles were used, based on the British 1990 growth reference charts. Patients were assigned to 1 of 3 groups based on their BMI percentile: low, normal and high BMI. A high BMI was defined as >85^th percentile for age and gender, whilst underweight was defined as <5^th percentile.

Results

Data was collected on 385 children with SCD in a single tertiary Paediatric Haemoglobinopathy centre in London. 16.6% children with SCD were overweight or obese and 5.2% were underweight. In contrast, government figures indicate that in the South London Borough of Southwark, up to 28% children aged 10-11 years were overweight or obese and 0.9% children were underweight in 2016-2017 (data.london.gov.uk). A high BMI among our SCD patients was associated with HbSC genotype (P= 0.006) and females (P=< 0.001). HbSS patients taking hydroxycarbamide had a significantly higher mean BMI compared to those not taking it (P=0.006). No association was found between BMI group and the number of acute sickle cell-related A&E attendances or hospital admissions for HbSS patients (P=0.450 and 0.780 respectively) or HbSC patients (P=0.838 and P=0.750 respectively). Patients with HbSS SCD in the high BMI group had a significantly higher haemoglobin (Hb) and fetal Hb (HbF) than those in the normal BMI group (P=<0.001 and P=0.010 respectively). HbSS patients in the high BMI group had a significantly lower absolute reticulocyte count (ARC) than those in the normal BMI group (P=0.022), see Table 1. These results suggest that HbSS patients with a high BMI may have a less severe disease than those with a normal BMI. These associations were not demonstrated in patients with HbSC disease.

Conclusions

Nearly one-sixth of children and adolescents with SCD in this urban population were overweight or obese. The association of hydroxycarbamide therapy and higher BMI in children with HbSS has been demonstrated in this study for the first time. There was no association between BMI group and the number of acute sickle cell-related A&E attendances or hospital admissions. In patients with HbSS disease, laboratory markers of disease severity, including Hb, HbF and ARC, suggest than patients with a high BMI may have a less severe disease than those with a normal BMI. Longitudinal studies monitoring BMI of children over time and markers of severity in SCD would produce greater evidence of the impact of a high BMI on disease severity.

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