Lung function decline in children with sickle cell disease treated with hydroxyurea

To the Editor: Sickle cell disease (SCD), the most common form of an inherited hematological disorder, is caused by a genetic variant that leads to the synthesis of an abnormal hemoglobin, HbS.Deoxygenated HbS tends to polymerize which results in a distortion of the red blood cell shape causing vaso-occlusion and end-organ damage.The most severe forms of SCD are homozygous HbSS and HbSβ 0 -thalassemia.The latter is characterized by compound heterozygosity for HbS and a non-functional beta-thalassemia gene.Milder forms of SCD include compound heterozygous conditions, such as HbSC.SCD is a systemic disease, associated with episodes of acute illness and chronic solid organ damage, including SCD lung disease. 1 Prior to therapy with hydroxycarbamide, also called hydroxyurea (HU), in SCD HbSS untreated children suffered from severe and progressive SCD lung disease with annualized declines in pulmonary function testing (PFT) similar to cystic fibrosis.2 Male sex was associated with a more rapid PFT decline in HbSS children not treated with HU, and HbSC genotype was associated with less lung disease compared to HbSS. 2HU is a disease-modifying agent that increases HbF production, total hemoglobin concentration, as well as red blood cell survival, and has been used for SCD therapy for decades.In adults, HU therapy results in a remarkable reduction in morbidity and mortality.3 An earlier, preliminary study in a small pediatric cohort had suggested that HU therapy in SCD children may lead to improvement in PFT decline.4 However, longitudinal data on lung disease progression and risk factors associated with PFT decline in current, larger pediatric cohorts of SCD HbSS treated with HU or HbSC are lacking.The aim of this study therefore was to quantify lung disease progression in a large cohort of SCD HbSS children treated with HU according to current guidelines, and to analyze the potential effects of sex on lung function decline in children with HbSS or HbSC.Longitudinal PFT results were analyzed in a cohort of children with SCD treated at the Hospital for Sick Children, Toronto, Canada, between 1997 and 2022.The study was approved by the local Research Ethics Board (REB# 1000078457).Patients with either HbSS or with HbSC and 5 to 18 years of age attending SCD outpatient clinic who performed PFT as part of routine clinical care were included.Patients were identified by searching the respiratory medicine PFT database for a physician diagnosis of " sickle cell disease" or

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