Sickle cell nephropathy (SCN) is a progressive complication of sickle cell disease (SCD) that
begins in childhood and results in renal (kidney) failure and early mortality in nearly 12%
of adults with hemoglobin SS (HbSS). The potential for prevention and reversal of kidney
damage in SCD is not known. Albuminuria is a commonly used biomarker of glomerular damage;
however the correlations of albuminuria with specific measurements of glomerular function and
pathophysiology have not been determined. The investigators hypothesize that in patients with
persistent albuminuria despite treatment of SCD with hydroxyurea, losartan will reverse
kidney dysfunction in early stage nephropathy and ameliorate progressive kidney dysfunction
in more advanced nephropathy. The primary aim is to study the acute and longer-term effects
of losartan (study drug) on specific glomerular functions in children and adults with SCD who
have persistent albuminuria. Research glomerular function tests will be done at study entry
(prior to taking losartan), 1 month, and 1 to 2 years after starting losartan therapy
(participants may take losartan for up to 24 months). In addition, participants are seen each
month in clinic and assessed by their regular clinical team. The second aim is to assess the
correlation of changes in albuminuria after 1 month of losartan with changes in direct
measurements of glomerular function at 12-24 months, thus determining if the magnitude of the
initial decrease in albuminuria in response to losartan predicts sustained improvements in
renal function.