Clinical Utility of Urinary N-Acetyl-β-D-Glucosaminidase (NAG), Kidney Injury Molecule-1 (KIM-1), and Diffusion-Weighted Renal MRI for the Early Detection of Sickle Cell Nephropathy in Children

Sickle cell disease was the first condition to be understood as a molecular disease, as described by Pauling and colleagues in 1949, and later helped to elucidate principles of gene expression, haemoglobin switching, and globin gene regulation.

Sickle cell disease refers to a group of inherited red blood cell (RBC) disorders caused by pathogenic variants in the HBB gene, resulting in the production of sickle haemoglobin S (HbS). Individuals with one copy of the mutation have sickle cell trait a condition that confers partial protection against severe malaria while those with pathogenic variants on both alleles develop the clinical syndrome of sickle cell disease.

The defining pathophysiological mechanism of sickle cell disease is the polymerization of deoxygenated HbS, leading to red cell sickling, haemolysis, and vaso-occlusion accompanied by a cascade of complex pathophysiological events. This cascade drives the multisystem complications of the disease, including acute painful crisis, acute chest syndrome, stroke and cognitive impairment, and progressive organ damage.

Sickle nephropathy often begins in childhood with impaired urine concentrating ability and glomerular hyperfiltration, eventually progressing to albuminuria, reduced glomerular filtration rate, and end-stage renal disease.

Up to one-third of adults with sickle cell disease develop overt proteinuria or decreased glomerular filtration rate, and kidney dysfunction is independently associated with early mortality. Hydroxyurea and angiotensin-converting enzyme inhibitors remain first-line therapies for reducing albuminuria and slowing progression.

Early onset SCN is a progressive kidney complication in SCD driven by chronic RBC sickling, vascular occlusion and hemolysis, typically begins in early childhood with hyperfiltration, hyposthenuria, and microalbuminuria.

Enuresis is another frequent complication that affects quality of life. Genetic modifiers, such as high fetal hemoglobin (HbF) levels and α-thalassemia trait have a protective effect on nephropathy, possibly by reduced hemolysis and endothelial stress.

Renal damage is common in children patients with SCD, which begins in childhood, progressing with age, a fact that makes nephropathy one of the possible complications. This can compromise patients' quality of life and decrease survival.

Sickle cell nephropathy (SCN) is a severe complication of SCA, characterized by early, often asymptomatic onset in childhood and a potential progression to chronic kidney disease (CKD) . SCN presents a significant challenge in the clinical management of patients with sickle cell anemia, contributing to a reduction in life expectancy by approximately 20 to 30 years. The clinical progression of SCN is age-dependent, with renal dysfunction typically emerging during childhood and gradually advancing to chronic kidney disease and, ultimately, kidney failure by the third or fourth decade of life.

Classical biomarkers such as creatinine, are not able to detect early renal lesions, which makes kidney injury molecule-1 (Kim-1) and N-acetyl-b-D-glucosaminidase (NAG) possible biomarker candidates in the prediction of renal disease in sickle cell anemia patients.

Despite advancements in treatment of sickle cell disease (SCD), hydroxyurea, a ribonucleotide reductase inhibitor, remains the cornerstone of therapy. While its primary effect is the elevation of fetal hemoglobin (HbF), hydroxyurea's mechanisms of action are multifaceted. Hydroxyurea (HU) reduces leukocyte and platelet counts, decreases the expression of endothelial adhesion molecules CD36 and CD49d, and increases nitric oxide and cyclic nucleotide levels, which may facilitate vascular dilation and further HbF induction.

Inclusion criteria

• • Children and adolescents aged less than 18 years.

• Confirmed diagnosis of sickle cell disease by hemoglobin electrophoresis and/or high-performance liquid chromatography (HPLC).
• Clinically stable patients at the time of enrollment, with no acute vaso-occlusive crisis or acute illness.

Exclusion criteria

• • Age ≥18 years.

• Acute sickle cell crisis at least 3 week prior to sample collection
• Acute infection or fever.
• Known chronic kidney disease due to causes other than sickle cell disease.
• Congenital renal anomalies.
• Diabetes mellitus.
• Hypertension.
• Current use of nephrotoxic medications.