Fanconi Syndrome Secondary to Deferasirox in Diamond-Blackfan Anemia: Case Series and Recommendations for Early Diagnosis

Kidney Tubular Damage Secondary to Deferasirox: Systematic Literature Review

Deferasirox is a first-line therapy for iron overload that can sometimes cause kidney damage. To better define the pattern of tubular damage, a systematic literature review was conducted on the United States National Library of Medicine, Excerpta Medica, and Web of Science databases. Twenty-three reports describing 57 individual cases could be included. The majority (n = 35) of the 57 patients were ≤18 years of age and affected by thalassemia (n = 46). Abnormal urinary findings were noted in 54, electrolyte or acid–base abnormalities in 46, and acute kidney injury in 9 patients. Latent tubular damage was diagnosed in 11 (19%), overt kidney tubular damage in 37 (65%), and an acute kidney injury in the remaining nine (16%) patients. Out of the 117 acid–base and electrolyte disorders reported in 48 patients, normal-gap metabolic acidosis and hypophosphatemia were the most frequent. Further abnormalities were, in decreasing order of frequency, hypokalemia, hypouricemia, hypocalcemia, and hyponatremia. Out of the 81 abnormal urinary findings, renal glucosuria was the most frequent, followed by tubular proteinuria, total proteinuria, and aminoaciduria. In conclusion, a proximal tubulopathy pattern may be observed on treatment with deferasirox. Since deferasirox-associated kidney damage is dose-dependent, physicians should prescribe the lowest efficacious dose.

Deferasirox-associated Fanconi syndrome in adult patients with transfusional iron overload

BACKGROUND AND OBJECTIVES

Deferasirox is an oral chelator approved for iron overload, which has a potential side effect of renal Fanconi syndrome, with proximal tubular dysfunction and tubular acidosis. Monitoring of renal function is recommended, though no standard for monitoring exists. We aim to describe cases of deferasirox-associated Fanconi syndrome in adults and the renal monitoring required to detect these findings.

MATERIALS AND METHODS

We present a review of the literature and six cases from our institution of deferasirox-associated partial Fanconi syndrome in adult patients with transfusional iron overload secondary to β-thalassemia or Diamond Blackfan Anaemia.

RESULTS

While prior cases in the literature occurred at high doses of deferasirox, our series included patients on doses as low as deferasirox 10 mg/kg who had been aggressively chelated. All patients had resolution of laboratory abnormalities with drug interruption.

CONCLUSION

Rather than chelating to normal iron levels, this series supports prior suggestions that deferasirox dose be reduced if ferritin <500-1000 ng/ml, and also supports dose reduction if liver iron content <3 mg iron per g dry weight or for those undergoing aggressive chelation with rapid decrease in iron. Monitoring with metabolic panel and urinalysis were sufficient to detect clinically significant proximal tubular dysfunction, but should be followed up with additional studies to confirm the diagnosis while deferasirox dose is decreased or held.

Proximal renal tubular acidosis with and without Fanconi syndrome

Proximal renal tubular acidosis (RTA) is caused by a defect in bicarbonate (HCO₃⁻) reabsorption in the kidney proximal convoluted tubule. It usually manifests as normal anion-gap metabolic acidosis due to HCO₃⁻ wastage. In a normal kidney, the thick ascending limb of Henle’s loop and more distal nephron segments reclaim all of the HCO₃⁻ not absorbed by the proximal tubule. Bicarbonate wastage seen in type II RTA indicates that the proximal tubular defect is severe enough to overwhelm the capacity for HCO₃⁻ reabsorption beyond the proximal tubule. Proximal RTA can occur as an isolated syndrome or with other impairments in proximal tubular functions under the spectrum of Fanconi syndrome. Fanconi syndrome, which is characterized by a defect in proximal tubular reabsorption of glucose, amino acids, uric acid, phosphate, and HCO₃⁻, can occur due to inherited or acquired causes. Primary inherited Fanconi syndrome is caused by a mutation in the sodium-phosphate cotransporter (NaP_i-II) in the proximal tubule. Recent studies have identified new causes of Fanconi syndrome due to mutations in the EHHADH and the HNF4A genes. Fanconi syndrome can also be one of many manifestations of various inherited systemic diseases, such as cystinosis. Many of the acquired causes of Fanconi syndrome with or without proximal RTA are drug-induced, with the list of causative agents increasing as newer drugs are introduced for clinical use, mainly in the oncology field.

Beta-thalassemia: renal complications and mechanisms: a narrative review

OBJECTIVES

Beta-thalassemias are a group of recessively autosomal inherited disorders of hemoglobin synthesis, which, due to mutations of the beta-globin gene, lead to various degrees of defective beta-chain production, an imbalance in alpha/beta-globin chain synthesis, ineffective erythropoiesis, and anemia. Improved survival in thalassemic patients has led to the emergence of previously unrecognized complications, such as renal disease.

METHODS

A comprehensive literature review through PubMed was undertaken to summarize the published evidence on the epidemiology and pathophysiology of renal disease in thalassemia. Literature sources published in English since 1990 were searched, using the terms beta-thalassemia, renal disease.

RESULTS

Renal disease is considered to be the 4th cause of morbidity among patients with transfusion dependent thalassemia. Chronic anemia, hypoxia and iron overload are the main mechanisms implicated in development of renal injury, whereas several studies also suggested a contributive role of iron chelators.

DISCUSSION AND CONCLUSION

Kidney disease may develop through progressive renal tubular and glomerular damage; thus, its early recognition is important in order to prevent and/or reverse deterioration. This review will provide an insight on the involved mechanisms implicated in kidney disease in thalassemic patients and will discuss the updates on diagnosis and prevention of renal complications in thalassemia.

Acute kidney injury: emerging pharmacotherapies in current clinical trials

Acute kidney injury (AKI) is a significant source of morbidity and mortality in pediatric patients, affecting more than one quarter of critically ill children. Despite significant need, there are no targeted therapies to reliably prevent or treat AKI. Recent advances in our understanding of renal injury and repair signaling pathways have enabled the development of several targeted pharmaceuticals. Here we review emerging pharmacotherapies for AKI that are currently in clinical trials. Categorized by their general mechanism of action, the therapies discussed include anti-inflammatory agents (recAP, AB103, ABT-719), antioxidants (iron chelators, heme arginate), vasodilators (levosimendan), apoptosis inhibitors (QPI-1002), and repair agents (THR-184, BB-3, mesenchymal stem cells).

Renal complications in thalassemia

Thalassemia is a disease with an extensive morbidity profile affecting almost every organ system. Renal involvement, once considered rare, is an underestimated and poorly studied complication that has been on the rise ever since medical advances granted patients longer life spans. Several studies and reports have emerged recently to shed light on the seriousness of this complication, although data is still lacking in terms of pathophysiology, diagnosis, prevention and treatment. In this review, we evaluate and compare renal involvement in the transfusion-dependent and independent variants of β-Thalassemia, highlighting the pathophysiology of kidney damage that involves iron overload, chronic anemia, and iron chelation therapy. An in-depth and focused review of the types of injuries incurred is also presented along with the diagnostic biomarkers accompanying each type of injury. Most research so far has focused on the transfusion-dependent thalassemia population being the group with most renal involvement, however recent reports have shown evidence of comparable, if not worse, involvement of the non-transfusion dependent population, sometimes leading to end-stage renal disease. As such, we try to shed light on distinct renal involvements in NTDT whenever available.

Iron overload in hematological disorders

While most common symptom of impairment of iron homeostasis is iron deficiency anemia, some hematological disorders are associated with iron overload (IO). These disorders are related mainly to chronic severe hemolytic anemia, where red blood cells (RBC) or their precursors are destroyed prematurely (hemolyzed), leading to anemia that cannot be compensated by increased production of new RBC. In such cases, IO is mainly due to repeated RBC transfusions and/or increased uptake of iron in the gastrointestinal tract. Normally, iron is present in the plasma and in the cells bound to compounds that render it redox inactive. Iron overload leaves a fraction of the iron free (labile iron pool) and redox active, leading to the generation of excess free radicals such as the reactive oxygen species. This condition upsets the cellular redox balance between oxidants and antioxidants, leading to oxidative stress. The free radicals bind to various cellular components, thereby becoming toxic to vital organs. Oxidative stress may also affect blood cells, such as RBC, platelets and neutrophils, exacerbating the anemia, and causing recurrent infections and thrombotic events, respectively. The toxic effect of IO can be decreased by treating the patients with iron chelators that enter cells, bind free iron and remove it from the body through the urine and feces. Iron toxicity may be also ameliorated by treatment with anti-oxidants that scavenge free radicals and/or correct their damage. The use of iron chelators is widely accepted when started in young patients with severe chronic anemia, but is still debatable as a therapeutic modality for older patients suffering from IO due to myelodysplastic syndromes. It should be noted that in addition to preventing iron toxicity, some compounds with iron chelator activity may also benefit other aspects of hematological disorders. These aspects include stimulation of platelet production, inhibition of leukemic cell proliferation and induction of their differentiation. Compounds with such multiple activities may prove beneficial for at least some patients with leukemia and myelodysplastic syndromes.

Long-term safety and efficacy of deferasirox in young pediatric patients with transfusional hemosiderosis: Results from a 5-year observational study (ENTRUST)

BACKGROUND

Children with red blood cell disorders may receive regular transfusions from an early age and consequently accumulate iron. Adequate iron chelation therapy can prevent organ damage and delayed growth/development. Deferasirox is indicated for treatment of pediatric patients with chronic iron overload due to transfusional hemosiderosis; however, fewer than 10% of patients in the registration studies were aged 2 to less than 6 years.

PROCEDURE

Deferasirox, a once-daily oral iron chelator, was evaluated in young pediatric patients with transfusional hemosiderosis during the observational 5-year ENTRUST study. Patients aged 2 to less than 6 years at enrollment received deferasirox according to local prescribing information, with the primary objective of evaluating safety, specifically renal and hepatic function. Serum ferritin was observed as a surrogate efficacy parameter.

RESULTS

In total, 267 patients (mean age 3.2 years) predominantly with β-thalassemia (n = 176, 65.9%) were enrolled. Mean ± standard deviation deferasirox dose was 25.8 ± 6.5 mg/kg per day over a median of 59.9 months. A total of 145 patients (54.3%) completed 5 years' treatment. The proportion of patients with two or more consecutive postbaseline measurements (≥7 days apart) of serum creatinine higher than age-adjusted upper limit of normal (ULN) and alanine aminotransferase more than five times the ULN was 4.4% (95% confidence interval [CI]: 2.1-7.9) and 4.0% (95% CI: 1.8-7.4), respectively. Median serum ferritin decreased from 1,702 ng/ml at baseline to 1,127 ng/ml at 5 years. There were no new safety signals.

CONCLUSIONS

Safety and efficacy of deferasirox in young pediatric patients in this long-term, observational study in everyday clinical practice were consistent with the known deferasirox profile.