The PKU (Phenylketonuria)
Association of NSW Inc.

What is PKU?

PKU or Phenylketonuria is a rare inherited (genetic) metabolic disorder, in which the liver cells cannot convert PHE (phenylalanine) to TYR (tyrosine). 

It affects one in ten thousand babies born in NSW each year. Although PKU is a very rare disorder, one in fifty individuals in the normal population are carriers of the gene that causes PKU. A person with PKU has inherited the defective gene from both parents and only occurs when both parents carry this gene, even then the chances of it being passed on are one in four.  All babies born in NSW undergo a compulsory blood screening process. This is done by a sample collected on a Guthrie Card by way of a heel prick, at approximately 4 day of age. If this shows an elevated level of phenylalanine  a follow up Guthrie card is organised. If this shows further elevated levels, the family  is asked to attend a specialised unit for advice. If PKU is diagnosed, the family is seen by a panel of clinicians and the diet is commenced immediately. Current research indicates that the diet should be continued for life. 

This metabolic disorder is a result of the liver being unable to produce an enzyme called phenylalanine hydroxylase. This breaks down an amino acid called phenylalanine. Phenylalanine is one of the amino acids that are present in all protein in our food. Protein is an essential ingredient of all living matter. A chemical compound made of building blocks called amino acids. Proteins have many uses in the body: they are used as building materials, chemical messages, regulators of chemical reactions, and so on. It is one of the essential amino acids, (i.e. ones that must be provided in the diet, as opposed to non-essential amino acids which can be produced in the body). In people unaffected by PKU the level of Phenylalanine in the blood is controlled by converting any excess to Tyrosine, another amino acid. In persons with PKU, PHE accumulates in the blood because their cells are unable to convert PHE to TYR.  This excess, left untreated by diet, can retard physical and intellectual development of the brain. Early diagnosis is essential because in the first two years of life the brain is growing rapidly. Tyrosine deficiency per se does not occur because the diet that people with PKU live on provides them with sufficient Tyrosine.

So far it all seems pretty grim, however, PKU is treated effectively with a low protein diet plus a supplement to provide tyrosine and extra vitamins and minerals that would be insufficient from the diet alone.  This diet is recommended for life and very restrictive on the food and quantities permitted. In fact, people with PKU are unable to eat meat, fish, poultry, nuts, cheese, bread, pasta, eggs, ice cream, dairy products. Foods that contain the artificial sweetener Aspartame which is a sweetener made from phenylalanine and aspartic acid (Nutrasweet, Canderal) have also to be avoided, so Diet Coke and similar drinks are out . This all sounds terrifying to the parents of a newly diagnosed child (it was for us) but with patience and practice it can be done. The PKU diet consists of measured amounts of fruits, vegetables as well as specially prepared substitutes or protein reduced foods. These foods are generally expensive, however this has been made more affordable with the introduction in 2001 of the Food Allowance from the Federal Government.

Because the diet is restrictive it does have an impact on "normal" habits, eating out requires some planning and thought but it not impossible. Perhaps the ones who feel it the hardest are our teenagers. Can you imagine being a hungry teenager whose daily limit of protein is equivalent to 2 slices of bread!

It was originally thought that the diet would cease when the brain was developed but it has since been shown that phenylalanine still has a significant effect on the central nervous system of PKU teenagers and adults.

The important thing to remember is that the dietary treatment of PKU has proved highly successful!! It leads to normal, happy, healthy and fit children who grow up into healthy teenagers and then healthy adults. The purpose of this association is to provide you with support from families who are on the same journey you are on.  

The PKU (Phenylketonuria) Association of NSW Inc.