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. Recent reports, however, suggest a more diminished role from PAT1 in some cases of the disorder.While PAT2 is strongly indicated as the primary mutagen responsible for iminoglycinuria, the variability of the phenotype is found to be instituted by three modifying genetic mutations. The major one among these is believed to be system IMINO.Defined as the sodium-dependent proline transporter not inhibited by alanine, system IMINO, believed to be formed by the SLC6A20 (SIT1) gene, is a crucial mammalian transport mechanism responsible for both renal reabsorption and intestinal absorption of proline and other imino acids, such as hydroxyproline and pipecolate. The mRNA sequence for SIT1 is expressed in a great deal of the gastrointestinal tract, including the stomach, duodenum, jejunum, ileum, cecum and colon. It is also found in the kidney, optical choroid, and parts of the central nervous system such the brain and microglial cells.Reduced penetrance is a phenomenon where a fully inherited genetic trait, such as a disease or disorder, fails to exhibit the expected phenotype. This has been reported in some cases of iminoglycinuria. Here, system IMINO is thought to play a role in reduced penetrance of iminoglycinuria by compensating for imino acid malabsorption related specifically to mutations of PAT2.
Conversely, SIT1 mutations are believed to result in full expression of iminoglycinuria in some cases where heterozygous mutations of PAT2 would otherwise have only been sufficient to cause hyperglycinuria.Two other transport systems are believed to play subsequent roles in iminoglycinuria, when mutations in them are present. The neutral amino acid transporter SLC6A19 (affecting glycine, proline, and other neutral amino acids like cysteine and tryptophan), associated with Hartnup disease, plays a role in iminoglycinuria as a modifier to PAT2 mutations and is also directly affected by the actions of SIT1. The glycine-specific transporter, SLC6A18, also has an effect on the iminoglycinuria phenotype by either compounding or compensating for failures of glycine transport.To summarize, iminoglycinuria is primarily expressed by homozygous mutations of the PAT2 renal transporter, while the overall iminoglycinuria phenotype may be modified by normal or defective activity of SIT1 (IMINO), SLC6A19 and SLC6A18. Diagnosis
Treament
See also
Pipecolic acid
Facilitated diffusion
Oral rehydration therapy

References


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