Phenylketonuria or PKU is a genetic disorder in which the body is unable to break down the essential amino acid phenylalanine into tyrosine. This is a complex and relatively rare disorder of the metabolic pathways. It is caused by an autosomal recessive gene. This means that if there are two parents who carry the gene, there is a 1 in 4 chance of the child being born with the condition. The condition can be managed if diagnosed early but if the early signs are not diagnosed in a newborn, the disease will cause severe progressive mental retardation. This is a disease that has quite a recent history when it comes to its understanding and pathogenesis.
The problem begins with an enzyme called phenylalanine hydroxylase or PAH. This is the enzyme that allows the body to breakdown phenylalanine to tyrosine. Tyrosine is a base amine that is used for the creation of a whole range of other products in the body like melanin in the skin, and the most important – neurotransmitters dopamine, epinephrine, and norepinephrine. In PKU, the defective gene prevents the creation of PAH. This causes an accumulation of phenylalanine and its conversion to phenylketone. This substance is toxic in the body and causes mental retardation in newborns. People who can control their phenylketone levels still continue to have problems later on in life as well. There is no cure for this condition since the fundamental problem lies in an enzymatic deficiency. The only management for this disease is to reduce the amount of dietary intake of phenylalanine. This is not dangerous despite it being an essential amino acid since it is only a precursor to other amino acids like tyrosine.
A very large range of foods contain phenylalanine and the most abundant source of this is milk of any kind. This means that dairy in all forms has to be eliminated. This also means that a meat based diet is absolutely impossible to be indulged in. Legumes are also not allowed when one is suffering from PKU. Monitoring this disease should be done by regular urine testing. The unfortunate part of this entire equation is that the sources of tyrosine are the same as phenylalanine. This means that some kind of nutritional supplement would need to be taken along with the diet to ensure that the levels of phenylalanine do not become a problem. Worth noting is that the mixing body fluids with another afflicted person becomes dangerous for the receiver.