Fanconi Syndrome and Other Proximal Tubule Disorders
Fanconi syndrome is a global dysfunction of the proximal tubule characterized by glycosuria, phosphaturia, generalized aminoaciduria, and type 2 renal tubular acidosis. Often there is hypokalemia, sodium wasting, hypouricemia, and dehydration. In children it typically is caused by inborn errors of metabolism, principally cystinosis. In adults it is mainly caused by medications, exogenous toxins, and heavy metals. Treatment consists of treating the underlying cause and replacing the lost electrolytes and volume. Cystinosis is a rare disorder of children caused by the intralysosomal storage of the amino acid cystine that leads to multiorgan dysfunction over time, especially renal failure. Cysteamine removes cystine from the lysosome and helps prevent renal failure and other complications of the stored cystine. Renal glycosuria is a benign disorder caused by a mutation in the gene coding for the SGLT2 glucose transporter, the target for a new class of medications to treat type 2 diabetes. Cystinuria is an autosomal recessive disorder that leads to impaired renal reabsorption of four amino acids (cystine, lysine, ornithine, and arginine) and accounts for about 1% to 2% of kidney stones. Cystinuria is treated by increasing fluid intake, alkalinizing the urine, and a thiol compound such as penicillamine or tiopronin.
