Fanconi Syndrome

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.

When Low Bone Mineral Density and Fractures Is Not Osteoporosis

PURPOSE OF REVIEW

To review the differential diagnosis of low bone mineral density (BMD).

RECENT FINDINGS

Osteoporosis is the most common cause of low BMD in adults; however, non-osteoporotic causes of low BMD should be considered in the differential diagnosis of patients with low BMD. Mild osteogenesis imperfecta, osteomalacia, and mineral and bone disorder of chronic kidney disease as well as several other rare diseases can be characterized by low BMD. This review summarizes the differential diagnosis of low BMD. It is important to differentiate osteoporosis from other causes of low BMD since treatment regimens can vary tremendously between these different disease processes. In fact, some treatments for osteoporosis could worsen or exacerbate the mineral abnormalities in other causes of low BMD.

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.