Long Term Effects of Hydroxyurea Therapy in Children With Sickle Cell Disease

Many years of study have documented the severe effects of sickle cell disease. Some of these
effects include hemolysis (the break down of red blood cells), blockages in the blood
vessels, and damage to the organs systems of the body. Hydroxyurea, which is given by mouth,
is used to effectively prevent blockages in the blood vessels of patients with sickle cell
disease. The hydroxyurea dosage varies and the responses of the body to this drug are not
well understood.

This study will follow sickle cell patients being treated with hydroxyurea for a long period
of time to evaluate the long-term cellular and molecular effects of the drug on the patients'
body. This study will consist of two patient groups. One group will be made up of patients
who have received hydroxyurea therapy before entering the study (Old Cohort). The second
group will be made up of patients who have not received hydroxyurea before study entry (New
Cohort).

This is not a therapeutic drug trial. Subjects for this study will receive hydroxyurea
therapy for accepted clinical indications, and will be treated per best clinical management
using treatment algorithms established at St. Jude Children's Research Hospital and other
pediatric sickle cell programs across the United States. Hydroxyurea therapy data (such as
dosing and duration of therapy) will not be dictated by this study, but will be collected to
correlate with long-term outcomes. Hydroxyurea dose escalation to a stable MTD will occur
according to published guidelines.

Inclusion Criteria:

- Patients from birth up to age 30 years

- Diagnosis of sickle cell disease

- Patients who are receiving hydroxyurea therapy or plan to begin hydroxyurea therapy