A case study of adult-onset hypophosphatemic osteomalacia with idiopathic fanconi syndrome

An Interesting Case of Acquired Renal Fanconi Syndrome

Renal Fanconi syndrome (RFS) is a proximal tubular dysfunction characterized by abnormalities in the absorption of electrolytes and substances by the proximal tubule. It can manifest as proteinuria, glycosuria, aminoaciduria, phosphaturia, and proximal renal tubular acidosis (RTA) type 2. Heavy metal-induced nephrotoxicity from heavy metals such as iron, cadmium, mercury, and lead is a common risk factor for type 2 RTA. Environmental contamination or prolonged contact with pesticides, such as lead arsenate, Bordeaux mixture, and copper sulfate, may also contribute to heavy metal exposure. A 25-year-old female patient with RFS was diagnosed, and the bicarbonate loading test showed typical features of generalized proximal tubular dysfunction and proximal RTA. A metabolic disorder in the bone was the predominant feature, and renal wasting of phosphorus and calcium was linked to osteoporosis and increased intact parathyroid hormone (PTH) levels. Due to reports of zoledronate-induced RFS, calcitriol was administered instead of bisphosphates. Drug-induced nephrotoxicity is the most probable cause of adult-onset RFS. Acute tubulointerstitial nephritis is a plausible hypothesis, and treatment was based on observations and assessments that improved clinical outcomes. Ayurvedic medicine, popular in India due to its traditional roots and cultural aversion to artificial drugs, has high levels of heavy metal content.

Altered Serum Uric Acid Levels in Kidney Disorders

Serum uric acid levels are altered by kidney disorders because the kidneys play a dominant role in uric acid excretion. Here, major kidney disorders which accompany hyperuricemia or hypouricemia, including their pathophysiology, are discussed. Chronic kidney disease (CKD) and hyperuricemia are frequently associated, but recent clinical trials have not supported the pathogenic roles of hyperuricemia in CKD incidence and progression. Diabetes mellitus (DM) is often associated with hyperuricemia, and hyperuricemia may be associated with an increased risk of diabetic kidney disease in patients with type 2 DM. Sodium-glucose cotransporter 2 inhibitors have a uricosuric effect and can relieve hyperuricemia in DM. Autosomal dominant tubulointerstitial kidney disease (ADTKD) is an important hereditary kidney disease, mainly caused by mutations of uromodulin (UMOD) or mucin-1 (MUC-1). Hyperuricemia and gout are the major clinical manifestations of ADTKD-UMOD and ADTKD-MUC1. Renal hypouricemia is caused by URAT1 or GLUT9 loss-of-function mutations and renders patients susceptible to exercise-induced acute kidney injury, probably because of excessive urinary uric acid excretion. Hypouricemia derived from renal uric acid wasting is a component of Fanconi syndrome, which can be hereditary or acquired. During treatment for human immunodeficiency virus, hepatitis B or cytomegalovirus, tenofovir, adefovir, and cidofovir may cause drug-induced renal Fanconi syndrome. In coronavirus disease 2019, hypouricemia due to proximal tubular injury is related to disease severity, including respiratory failure. Finally, serum uric acid and the fractional excretion of uric acid are indicative of plasma volume status; hyperuricemia caused by the enhanced uric acid reabsorption can be induced by volume depletion, and hypouricemia caused by an increased fractional excretion of uric acid is the characteristic finding in syndromes of inappropriate anti-diuresis, cerebral/renal salt wasting, and thiazide-induced hyponatremia. Molecular mechanisms by which uric acid transport is dysregulated in volume or water balance disorders need to be investigated.

Type 2 renal tubular acidosis presenting with joint pain: A case report and literature review

Fanconi syndrome (FS) can present with hypophosphatemia, renal glycosuria, hypouricemia and aminoaciduria. Phosphate depletion is the most critical clinical aspect of FS as it leads to osteomalacia. Some patients present with symptoms and signs related to hypophosphatemic osteomalacia (HO). Thus, these patients present with these symptoms and are misdiagnosed. From an investigation of the published literature, HO symptoms are found to be non-specific and were thus misdiagnosed in various centers. The present study describes the case of a a 46-year-old male with FS who suffered from joint pain and was first misdiagnosed. After he was referred to the authors' hospital, his case was evaluated and following a consideration of the results of this evaluation, he was diagnosed with idiopathic FS with multiple osteoporotic fractures. Furthermore, the present study performs a brief literature review other cases of patients that were misdiagnosed and whose symptoms were later found to be due to HO are also discussed. It is hoped that the present study may increase the awareness of HO among physicians and may help to draw attention to such cases of patients presenting with non-specific symptoms.

Invasive Pneumococcal Disease Associated with Fanconi-Like Syndrome

Acquired causes of Fanconi syndrome in adults are usually due to drugs, toxins or paraproteinaemias. Infectious causes are rarely described. We report a case of invasive pneumococcal disease in a patient who developed a Fanconi-like syndrome during the course of her illness. This patient presented with multiple electrolyte derangements consisting predominantly of hypokalaemia, hypomagnesaemia and hypophosphataemia during hospitalization for invasive pneumococcal disease with possible Austrian syndrome. Further evaluation revealed significant urinary losses of these electrolytes, uric acid and β2-microglobulin. Together with evidence of hypouricaemia, this is suggestive of proximal renal tubulopathy, and hence a Fanconi-like syndrome. The patient’s clinical condition and biochemical anomalies improved following pneumococcus treatment.

Adult Idiopathic Renal Fanconi Syndrome: A Case Report

Renal Fanconi syndrome (RFS) is caused by generalized proximal tubular dysfunction and can be divided into hereditary and acquired form. Adult-onset RFS is usually associated with drug toxicity or systemic disorders, and modern molecular genetics may explain the etiology of previous idiopathic cases of RFS. Here, we report the case of a 52-year-old woman with RFS whose etiology could not be identified. She presented with features of phosphaturia, renal glucosuria, aminoaciduria, tubular proteinuria, and proximal renal tubular acidosis. Her family history was unremarkable, and previous medications were nonspecific. Her bone mineral density was compatible with osteoporosis, serum intact parathyroid hormone level was mildly elevated, and 25(OH) vitamin D level was insufficient. Her blood urea nitrogen and serum creatinine levels were 8.4 and 1.19 mg/dL, respectively (estimated glomerular filtration rate, 53 mL/min/1.73 m²). Percutaneous renal biopsy was performed but revealed no specific renal pathology, including mitochondrial morphology. No mutation was detected in EHHADH gene. We propose the possibility of involvement of other genes or molecules in this case of adult RFS.