What is the primary defect associated with Fanconi syndrome?

The primary defect associated with Fanconi syndrome is indeed a defect in the proximal tubule of the nephron. This condition impacts the kidneys' ability to reabsorb various substances that are normally reclaimed during the filtration process, including glucose, amino acids, bicarbonate, and phosphate.

In Fanconi syndrome, the proximal tubules fail to reabsorb these substances adequately, leading to their excessive loss in urine (renal wasting) and potentially causing metabolic disturbances. For instance, the loss of bicarbonate can lead to acidosis, while phosphate loss can result in bone demineralization.

The other parts of the nephron, such as the distal tubule, glomeruli, and collecting ducts, do not primarily have defects associated with Fanconi syndrome. Thus, the focus on the proximal tubule in this condition is fundamentally important in understanding its pathophysiology and related physiological consequences.