Phenylalanine is an amino acid that is required for cellular activity in the human body. It is converted to tyrosine, another amino acid, by a gene enzyme called phenylalanine hydroxylase in the body (PAH). An enzyme is a biological catalyst that aids a chemical reaction while remaining unharmed in the process. Tyrosine is required for the production of hormones, energy in the body, and the skin pigment melatonin.
The hydroxylation, or addition of an oxygen-hydrogen group to a part of the phenylalanine molecule, is the chemical process that produces tyrosine. This complex reaction takes place in the liver and involves the interaction of iron and other enzymes. Tyrosine is used by the body to make other important hormones, such as dopamine, which is used by the brain.
Humans get phenylalanine from the foods they eat, which includes most proteins and aspartame-containing artificial sweeteners. With a few exceptions, the body can normally regulate excess phenylalanine through the phenylalanine hydroxylase reaction. Some people lack PAH or have abnormalities that prevent the amino acid from being processed normally.
People with a PAH deficiency can suffer from severe mental retardation if the disease is not caught early. Phenylketonuria is a condition in which there is too much phenylalanine in the body. In many developed countries, newborns are tested at birth using the Guthrie assay, a blood test that looks for an excess of an amino acid combined with bacteria.
There are other symptoms of phenylalanine hydroxylase mutation in addition to the excess amino acid in urine. A musty odor is common in people with the deficiency, especially in their urine. They may also have pale skin due to a lack of tyrosine, which is required for melanin production. Due to a lack of key hormones required for nerve function, epilepsy and other nerve diseases can develop as a result of the disease.
On intelligence tests, children with undiagnosed PAH disease perform worse than healthy children. Severe mental problems and other medical conditions will develop if it is not treated. The development issues caused by the phenylalanine hydroxylase condition can be avoided by following a strict diet that avoids artificial sweeteners and has a low protein intake.
If PAH mutations are discovered in infants, they must be placed on a phenylalanine-restricted diet. Although all proteins contain the amino acid in varying amounts, animal proteins, nuts, and beans are especially high in it and should be avoided. The dietary restriction is a lifelong commitment, as there was no gene therapy available to replace phenylalanine hydroxylase until the twenty-first century. Because the body does not produce it and a normal dietary source is the restricted protein, tyrosine may need to be given as a supplement to people on diets.