Sickle cell disease is the most common inherited genetic disorder, accounting for 300,000 births worldwide per year. It is caused by an autosomal recessive mutation of the β-globin gene, responsible for an abnormal hemoglobin, the main protein in red blood cells, responsible for transporting oxygen from the lungs to the tissues. The abnormal hemoglobin, known as "Sickle" or S, deforms the red blood cell, causing chronic hemolytic anemia, organ damage (heart, spleen, etc.) and vaso-occlusive crises. Therapeutic progress and specialised patient follow-up have considerably improved the vital and functional prognosis of children and adolescents with sickle cell disease. Physical fitness, measured during a cardiorespiratory exercise test (CPET), is used to determine maximal oxygen uptake (VO2max). Patients with sickle cell disease have a multifactorial limitation of exercise tolerance, which may affect their physical fitness. Authors have shown that VO2max is impaired in children and adolescents with sickle cell disease, independently of their baseline hemoglobin level. Yet VO2max is a key determinant of health-related quality of life (HRQoL) in patients being monitored for a chronic disease. In the past, our team has contributed to the assessment of HRQoL in several groups of pediatric patients suffering from chronic disease (congenital heart disease, PAH). To date, the link between impaired physical fitness and HRQoL has not been demonstrated in sickle cell children. The pathophysiological determinants of reduced physical capacity and exercise tolerance in sickle cell patients have also not been fully elucidated. Studying these factors will enable us to propose appropriate treatment in the future, with the aim of improving physical fitness and HRQoL in children and adolescents with sickle cell disease.

This prospective case-control study included sickle cell children and healthy controls from 6 to 17 years old. Patients refuse the use of medical data will be excluded.

After description of the study sample, we will first compare the VO2max Z-score between cases and controls. We will correlate the VO2max to PedsQL self- and proxy-related and Ricci and Gagnon scores (use of the coefficient of correlation rhô). Then we will compare others CPET parameters and will determine associated factors of VO2max with others resting data : hematological, respiratory, cardiologic, anthropometric, educational (use of the coefficient of correlation rhô, and multivariate linear regression model).

Sickle cell children

Inclusion Criteria:

• Child from 6 to 17 years old, with a confirmed diagnosis of sickle cell disease (i.e., homozygous HbS/S or heterozygous HbS/C mutations), during their routine follow-up, having performed :
• a hematology consultation : physical examination, blood test
• a cardiology consultation : electrocardiogram, transthoracic echocardiography
• a respiratory plethysmography
• a CPET and to fill in the study questionnaires.

Exclusion Criteria:

• Parents' refusal to use medical data.

Healthy children

Inclusion Criteria:

• Child from 6 to 17 years old having performed a cardio-respiratory exercise test for chest pain, dyspnea on exertion, heart murmur and whose results do not find:
• Congenital heart disease (normal echocardiography and ECG)
• Respiratory disease (normal FEV1 and FVC)
• Child having performed a maximal cardio-respiratory stress exercise until exhaustion.

Exclusion Criteria:

• Child taking long-term drug treatment
• Child with chronic disease
• Parents' refusal to use medical data.

Sickle cell children cohort consisted of children with a genetic diagnosis of sickle cell disease (HbS/S or HbS/C), followed at the Department of Pediatrics of Montpellier University Hospital, a tertiary care academic institution in southern France.

Healthy children cohort consisted of children referred to a pediatric cardiologist for a nonsevere functional symptom related to exercise (murmur, palpitation, chest pain, and dyspnoea) or for a medical sports certificate. These children needed to have a completely normal check-up, including physical examination, ECG, and echocardiography. Children with any chronic disease, medical condition or medical treatment, and those requiring any further specialized medical consultation were not eligible.