The Methods of PKU Determination

Phenylketonuria (PKU) is a genetic condition that is inherited from both parents. PKU is usually diagnosed following a standard blood test shortly after birth. If PKU is detected late or left untreated, it can result in brain deficits, such as mental retardation. Research into PKU has revealed that careful dieting throughout life can prevent symptoms from developing.

Inheritance

• PKU is a genetic disorder. A gene inherited from both parents should function to produce an enzyme capable of breaking down an amino acid called phenylalanine. If there is a genetic disorder inherited from both parents, the enzyme is defective and phenylalanine cannot be broken down in the body. Phenylalanine is found in many foods such as meat and eggs. If eaten, toxic levels of phenylalanine build up in the body causing brain damage.

Symptoms

• If PKU is left untreated, it can cause mental retardation because a buildup of phenylalanine prevents amino acids from entering the brain. These amino acids are needed for development. The child may be hyperactive and present with a smaller-sized head. Other symptoms include seizures, rash and tremors. The child may develop a condition known as albinism, commonly referred to as albino. Albinism is a result of little skin pigmentation because of a lack of pigment, called melanin. This is formed from a breakdown product of phenylalanine. Because phenylalanine cannot be broken down, no melanin is produced. This causes the child to have blue eyes, light skin and very fair hair. Phenylalanine can even build up on the skin and breath. This is discernible as a musty smell.

PKU Determination

• Usually, the child is tested for PKU within two weeks of being born. The test removes a small amount of blood from the heel of the child. The blood sample is analyzed and the amount of phenylalanine is measured. The ratio between phenylalanine and its breakdown product is determined. If the ratio is high, further blood tests and urine tests confirm the diagnosis of PKU.

Treatment

• The main aim of treatment is to reduce the amount of phenylalanine in the body. The most effective way to do this is to limit dietary protein intake. This means reducing the amount of foods, such as meat, eggs, cheese, bread, fish and milk. The diet has a large proportion of foods that contain little phenylalanine, such as fruits and vegetables. Aspartame is a sweetener that contains large amounts of phenylalanine and so should be avoided. The nutritional adequacy of the diet must be reviewed often by a specialist dietitian and phenylalanine blood levels should be monitored regularly. Supplements may be necessary to compensate for low levels of amino acids and nutrients.