A 6-month-old infant has poor weight gain, vomiting, episodic fevers, and chronic constipation. Laboratory studies reveal a urinalysis with a pH of 8.0, specific gravity of 1.010, 1+ glucose, and 1+ protein. Urine anion gap is normal. Serum chemistries show a normal glucose and a normal albumin with a hyperchloremic metabolic acidosis. Serum phosphorus and calcium are low. What is the best diagnosis to explain these findings?

The nonspecific findings of anorexia, polydipsia and polyuria, vomiting, and unexplained fevers, along with the more specific laboratory abnormalities of glucosuria but normal blood sugar, abnormally high urine pH in the face of mild or moderate serum hyperchloremic metabolic acidosis, and mild albuminuria in the presence of normal serum protein and albumin, suggest Fanconi syndrome (also called global proximal tubular dysfunction). Fan- coni syndrome can be hereditary or acquired; hereditary forms are usually secondary to a genetic abnormality such as cystinosis, galactosemia, Wilson disease, and some mitochondrial abnormalities. A number of agents can cause Fanconi syndrome, including gentamicin (or other aminoglycosides), outdated tetracycline, cephalothin, cidofovir, valproic acid, streptozocin, 6-mercaptopurine, azathioprine, cisplatin, ifosfamide, heavy metals (e.g., lead, mercury, cadmium, uranium, platinum), paraquat, maleic acid, and toluene (from sniffing glue). The mechanism of action of these agents is through acute tubular necrosis, alteration of renal blood flow, intratubular obstruction, or allergic reactions within the kidney itself. Many of these toxic effects are reduced or eliminated with removal of the offending agent. Renal tubular acidosis (RTA) type 1 is a distal RTA, and has a positive urine anion gap, as does RTA type 4. Type 3 is not a recognized type of RTA. Congenital nephrotic syndrome is a rare version of nephrotic syndrome, characterized by edema early in infancy, with hypoalbuminemia.