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Where on the Chromosome is the Problem?

Phenylketonuria is an inherited disease. It is found as a recessive allele. This means that both the mother and the father of a child must be carring the recessive trait for a child to be born with PKU. Phenylketonuria occurs on chromosome 12.

What Is the Problem?

There are 2 variations of Phenylketonuria, commonly called PKU. Classic PKU is the more severe of the two variations, cause by a mutation in the phenylalanine hydroxylase enzyme (PAH). Deficient hyperphenylalaninemia is the other type of PKU, which means that the phenylalanine hydroxylase enzyme is normal, but it is instead a problem in the recycling of BH4. Having PKU means that the body is unable to break down the amino acid phenylalanine, more commonly called Phe. When excessive Phe is consumed through protein, there is a buildup in the body which leads to many side effects, which can lead to mental incapacity in young children.

What is the Prognosis?

When a baby is born, they are put through a mandatory series of tests. The specific test that looks for children with PKU is called Guthrie test using tandem mass spectrometry. If detected early enough, a baby can live a normal life (picture above right side) as long as they say on a strict low Phenylalanine diet. Phenylalanine is an amino acid which is found in all forms of protein. The amount of protein a baby can have without causing severe damage varies from case to case. If a baby goes undetected, and consumes a lot of protein, they will start to have brain developmental problems. This will eventually lead to much more severe problems such as seizures and mental retardation. See picture above, boy on the left. Babies who follow the low protein diet from an early age can live normal lives. There are many side effects of having PKU, such as fair skin and fair hair, mild trouble in school, poor test taking, and an inability to concentrate. Additionally, adult females with PKU must strictly follow a low Phe diet before and throughout their entire pregnancy and breastfeeding.

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