[6] Iminoglycinuria is a rare and complex disorder, associated with a number of genetic mutations that cause defects in both renal and intestinal transport systems of glycine and imino acids.

Otherwise, it is thought to be a relatively benign disorder,[6][14] although symptoms associated with disruptions of proline and glycine metabolism caused by malabsorption may be present with iminoglycinuria.

[citation needed] A non-inherited cause of excess urinary excretion of proline and glycine, similar to that found in iminoglycinuria, is quite common to newborn infants younger than six months.

[4] Glycine, proline and hydroxyproline share common renal tubular mechanisms of reabsorption,[7] a function specific to the proximal tubule.

[4][5] Both reabsorption or absorption of glycine and imino acids takes place respectively at the proximal tubule or intestinal brush border epithelium.

[4] However, despite the role that intestinal malabsorption of glycine and imino acids can play in iminoglycinuria, the primary defect disrupts their renal transport and reabsorption.

[16] In mammals, including humans, the transport of amino and imino acids from the lumen (interior) of the intestine or the renal proximal tubule into the cells occurs at the brush border membrane of the epithelium (moist, tightly packed cellular lining of many tissues and organs of the body).

These findings delineate iminoglycinuria as the homozygous form of hyperglycinuria, with the former having a higher degree of urinary excretion of glycine and imino acids correlating to mutations in both alleles.

[30] As absorption and reabsorption of glycine, proline and hydroxyproline occurs through PAT1 as well, it is believed to play another role in expressing the malabsorptive iminoglycinuria phenotype.

[26][27] The mRNA sequence for SIT1 is expressed in a great deal of the gastrointestinal tract, including the stomach, duodenum, jejunum, ileum, cecum and colon.

[26] Reduced penetrance is a phenomenon where a fully inherited genetic trait, such as a disease or disorder, fails to exhibit the expected phenotype.