Aminoaciduria: Description, Causes and Risk Factors:
Aminoaciduria is an abnormal amount of amino acids in the urine. Amino acids are the building blocks for proteins in the body. The term aminoaciduria is applied when more than 5% of the filtered load is detected in the urine. It may result from an inherited metabolic abnormality, in which case the aminoaciduria is a permanent finding, or it may be an acquired abnormality which may either be transient or become permanent.
Three distinct groups of inherited aminoacidurias are distinguished, based on the net charge of the target amino acids at neutral pH:
Acidic (negative charge).
- Basic (positive charge).
- Neutral (no charge).
A deficiency in an enzyme resulting in a defect of amino acid metabolism is referred to as primary aminoaciduria.
- Defects in molecular transporters responsible for transport and absorption of an amino acid are classified as secondary aminoaciduria.
Both types of aminoaciduria may be inherited, mostly in an autosomal recessive pattern, but some may be acquired secondary to several diseases such as hyperparathyroidism, multiple myeloma, osteomalacia, rickets, and viral hepatitis.
Transient aminoacidurias may occur during the diuretic phase after acute renal insufficiency, or as a result of a deficiency of potassium.
Aminoacidurias of longer duration occur as a result of poisoning with heavy metals, particularly cadmium and uranium, but also with lead or mercury.
There is aminoaciduria found in patients with Wilson’s disease; it is associated with the toxic effect of copper on the renal tubule, which characteristically accumulates in patients with this disease.
Under normal circumstances, the renal tubules reabsorb in excess of 93% of the amino acids filtered from the plasma, influenced by the glomerular filtration rate (GFR). When the filtered load of amino acids is increased, there is an increase in both the amounts reabsorbed and those excreted. However, the ability of the renal tubule to respond to an increased filtered load of amino acids is so great that a maximum rate of reabsorption has not been found in the human. In some instances, the aminoaciduria is generalised; there is increased excretion of all of the amino acids occurring in the plasma. In other instances, the aminoaciduria is more specific, in that there are increased amounts of some amino acids in the urine while all others are excreted in normal amounts. Secondary or ‘overflow’ aminoaciduria can also be seen in conditions in which there is hyperaminoacidaemia.
Clinical symptoms include a light-sensitive skin rash, cerebellar ataxia, and occasional psychotic symptoms. They are not observed in all patients and usually cease after childhood when the demand of amino acids for protein biosynthesis decreases. Iminoglycinuria is a benign syndrome, defined by elevated amounts of proline, hydroxyproline, and glycine in the urine. The disorder is genetically complex. Because of the lack of clinical symptoms, iminoglycinuric individuals have only been identified during urine mass screening programs in the US, Canada, and Australia. Dicarboxylic aminoaciduria also appears to be a largely benign syndrome and is thought to arise from mutations in the apical aspartate/glutamate transporter EAAC1.
An Aminoaciduria test is done to screen the increased levels of amino acid in urine which indicates possible errors of metabolism caused by enzyme deficiency.A clear sample of urine is necessary to conduct this test. It is done at a pathological testing laboratory.Before this test is taken, another test is taken 24-hours before this test. This test takes a quantitative urine chromatography which is necessary to measure the elevated levels of specific amino acids.Increased level of amino acids is also shown in the blood plasma.If the test is performed early on young infants and the defect is treated, severe mental retardation can be prevented in the infant.Early tests may prevent many disorders like alkaptonuria, cystinosis, galactosemia, rickets, Wilson’s disease and other metabolism related disorders.
Since this disorder is also common among neonates, it is essential to perform the test only after the neonate has ingested dietary protein. But, it is difficult to perform this test on the neonate since the neonate would not always consume protein diet.
There is no known cure for aminoaciduria. Aminoaciduria is often treated with a restrictive diet, to minimize or eliminate exposure to a particular amino acid.
Treatment options may include:
- Increase liquids in the diet.
- Medications that alkalinize the urine: sodium bicarbonate, sodium citrate, vitamin supplements.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.