Iminodipeptiduria: a genetic defect in recycling collagen; a method for determining prolidase in erythrocytes

A 39-month-old girl was found to have a genetic deficiency of prolidase. This enzyme specifically splits dipeptides with proline or hydroxyproline at the C-terminus. Absence of the enzyme leads to massive urinary excretion of iminodipeptides. Clinical symptoms include some that can be ascribed to collagen defects. Previously we had demonstrated that the efficient recycling of proline by the breakdown and resynthesis of collagen is a normal physiological process. The collagen defects in this condition could result from interference with the normal recycling of collagen.