Amino acids are the molecules your body uses to create its proteins, control its cellular processes and break down and use the foods in your diet. One specific category of these acids, called essential amino acids, must come from dietary sources. Infants who don't get enough of the essential amino acids can develop serious or fatal health complications.
Essential Amino Acid Basics
Essential amino acids come from foods in your diet that contain protein. Like internal human proteins, animal and plant proteins are constructed from amino acids; when you eat protein-containing foods, your body breaks these proteins down and reuses their amino acid content. Infants and older children need 10 different dietary amino acids, including substances called arginine, histidine, leucine, isoleucine, lysine, phenylalanine, methionine, threonine, valine and tryptophan. Adults don't need arginine, and therefore only need to get the remaining nine essential acids from food sources.
Phenylalanine Processing
Human infants can inherit specific problems related to essential amino acid processing, according to the "Merck Manual Home Health Handbook." Newborns and infants born without the ability to process phenylalanine will develop a condition called phenylketonuria, or PKU. Normally, the body uses phenylalanine to form another amino acid, called tyrosine. However, in people with PKU, this transformation doesn't occur, and phenylalanine builds up to toxic levels and triggers progressive intellectual disabilities. Additional potential PKU symptoms include nausea, vomiting, rash, hyperactivity, self-injury and seizures. Children with PKU must restrict their phenylalanine intake for life.
Leucine, Isoleucine and Valine
Another inherited disorder in infants, called maple syrup urine disease, occurs when their bodies can't properly process the essential amino acids leucine, isoleucine and valine. Incomplete breakdown of these acids triggers a characteristic syrup-like urine smell, as well as symptoms that can range from vomiting and confusion to intellectual disability, nerve abnormalities, seizures, coma and infant death. Mild cases of maple syrup urine disease are treated with vitamin B-1, while more severe cases require treatment with the artificial kidney cleansing process called dialysis. In all cases, follow-up care depends on restricted intake of the associated essential amino acids.
Considerations
Infants can also inherit processing problems related to non-essential amino acids, the "Merck Manual" notes. These include tyrosinemia --- which is related to the processing of the amino acid tyrosine --- and homocystinuria, which is related to the processing of the amino acid homocysteine. Newborn children in the United States typically undergo blood testing that detects the presence of inherited disorders related to both essential and non-essential amino acids. Since tyrosine production is related to the body's supply of phenylalanine, people with PKU can also develop tyrosine deficiencies. Consult your child's doctor for more information on essential amino acids and related disorders in newborns.
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