A 2-year-old child is brought to his pediatrician because of failure to thrive and polyuria. He is found to have glucosuria on urinalysis, although his serum glucose is within normal limits. What renal defect is responsible for his condition?

Question

A 2-year-old child is brought to his pediatrician because of failure to thrive and polyuria.  He is found to have glucosuria on urinalysis, although his serum glucose is within normal limits.  What renal defect is responsible for his condition?

Quizplus · Accepted Answer

Glucose, bicarbonate, amino acids, calcium, and phosphate are normally filtered by the glomerulus and reabsorbed by the proximal tubule. When proximal tubular transport is defective (as in Fanconi syndrome), these substances appear in the urine despite being present at normal concentrations in serum. The classic signs and symptoms of Fanconi syndrome are caused by the loss of various substances in the urine.Fanconi syndrome can be inherited through autosomal dominant, autosomal recessive, or X-linked mechanisms. Clinical manifestations such as polyuria, polydipsia, and failure to thrive tend to occur in the first years of life. Increased calcium loss in urine leads to calcium mobilization from bones, which causes severe rickets. Hypercalciuria predisposes to nephrolithiasis. Glucosuria and low urinary pH trigger frequent and severe urinary tract infections. Urinalysis reveals the presence of glucose, amino acids, bicarbonate, calcium and phosphate in urine. Laboratory evaluation of these patients reveals hypokalemia (due to potassium loss) and metabolic acidosis (due to bicarbonate loss). (Choice A) Renal papillary necrosis manifests with flank pain, hematuria, and the excretion of tissue fragments in urine. Renal papillary necrosis is associated with sickle cell disease, diabetes mellitus, and urinary tract obstruction. (Choice B) Interstitial inflammation and fibrosis is characteristic of chronic interstitial nephritis. This condition usually occurs in adults as a result of chronic pyelonephritis, analgesic nephropathy, or metabolic abnormalities. Polyuria, nocturia, and urinary frequency are common. Glucosuria is not seen, however. (Choice C) Increased permeability of the glomerular membrane is characteristic of numerous glomerular disorders that manifest with nephrotic syndrome or nephritic syndrome. These disorders do not affect proximal tubular reabsorption. (Choice E) Multiple cysts within the renal parenchyma are seen in infantile polycystic kidney disease (ARPKD), which leads to oligohydramnios in utero. Affected children are usually born with signs of Potter syndrome (eg, pulmonary hypoplasia, flat facies, limb deformities) and can die of respiratory failure during the first months of life. Educational objective: Fanconi syndrome is an inherited disorder of proximal tubular transport. Glucose, bicarbonate, calcium, phosphate, and amino acids are lost, leading to a number of metabolic abnormalities. The classic clinical presentation includes failure to thrive, polyuria, polydipsia, and rickets.

A 2-Year-Old Child Is Brought to His Pediatrician Because of Failure