Phenylketonuria (PKU)

You are probably thinking phenylketo-what?  Well at least that is what I thought when my little boy was diagnosed.  Along with " why my little one" and I’d done this to him.  When in reality I hadn’t.

When a baby is about a week or so old they have a heel prick test (Guthrie).  Some midwives explain why this is done, or you get a leaflet with only a few lines saying what is picked up.  Usually you get the result in 7-10 days.  PKU affects 1 in 15000 births.  When a child is diagnosed with PKU the odds go right down to 1 in 4 chances of those parents having another baby with PKU together.

What Is PKU?

Phenylketonuria, which in short prevents normal breakdown of protein, due to an enzyme deficiency.  If it is left untreated it can lead to the growing child having severe mental handicaps and learning difficulties.

At birth the baby appears to be quite normal because Phenylketonuria is caused by a biochemical abnormality which is inherited by the child from both parents.  The result of a positive test show that the baby has too much of a substance called Phenylalanine in the blood.  Phenylalanine is a very natural part of all foods containing protein and is essential in a "normal" diet.

As soon as the babies diagnosis has been confirmed, baby can then be put onto a special low phenylalanine feed until the high levels are brought down to a normal reading.  This usually takes a few days and when the levels of phenylalanine are within a safe range, regular Guthrie tests are needed to calculate this so parents are taught how to perform these test properly, once the results are back the dietician will inform the parents that a small amount of breast or baby milk can be introduced to provide the limited amount of phenylalanine needed for normal growth.  Solid food can be introduced at weaning age about 4-6 months.  The dietician gives careful guidance at this sensitive time.  In general most vegetables and all fruits can be given as can some baby food.  During this time the small amount of phenylalanine may continue to come from the breast/baby milk until the time comes to replace it with measured amounts of everyday food, such as cereals and potatoes.  The dietician gives a very informative list of the specific food that will be allowed.  Foods with less than 0.5g of protein per 100g are allowed to be given freely (don’t have to be weighed) throughout the day if desired.  Care has to be taken with anything above that.  Normally foods start to be weighed when it is 1.0g per 100g.  For every 100g a low phenylalanine formula is given.  The diet will eventually expand to include a large range of low protein food which the doctor will prescribe.  These foods include special bread, biscuits, pasta, different pastry/cakes and bread mixes.

What Is Phenylalanine?

In a child with PKU proteins in food cannot be used in the proper way.  Foods which supply most protein in a "normal" diet include fish, eggs, poultry, milk, meats and cheese but a reasonable amount of protein is found in foods such as certain cereals and vegetables like rice, wheat, peas, beans and lentils.  All these proteins are made up of substances or 'building blocks' called amino acids.

There are lots of different types of amino acids and all protein food contains a varying amount.  That is why every protein food tastes and looks very different from one another. E.g. cheese doesn’t look or taste like red meat.

Phenylalanine is an amino acid and this particular amino acid cannot be processed properly by the PKU child.

This problem occurs whenever protein foods such as milk or meats are eaten.  Obviously the digestion starts in the stomach.  The first step in this process is for the links joining the amino acids together to be broken down.  Each of these individual acids, including the phenylalanine, is then absorbed into the bloodstream and used in different parts of the body for different purposes such as growth and tissue repair.  In babies and young children most of these amino acids including the phenylalanine is used for growth.  However, in a "normal "diet there are more than enough amino acids for growth and maintenance.  The extra acids are changed into other substances by special chemicals called enzymes. Each and every amino acid needs its very own enzyme to change it into another substance.  Usually, the excess phenylalanine is changed to an amino called tyrosine by an enzyme called phenylalanine hydroxylase.  Tyrosine is needed by our bodies to make many of the important substances such as hormones, brown pigment melanin and chemical messengers for the brain.  With Phenylketonuria, because the enzyme phenylalanine hydroxylase is missing or it is not working properly, the body cannot change the phenylalanine into tyrosine.  A small amount of phenylalanine can be changed into a substance called phenylketones which comes out in the urine, but this will only happen when there is a very high level of phenylalanine in the blood and tissue.  This gives quite a strong odour to urine.  In these circumstances the phenylketones can be detected in the urine.

The Low Phenylalanine Diet!

To treat the PKU the amount of phenylalanine in the diet must be reduced but only so there is still enough to provide just enough for tissue repair and growth but there cannot be an excess.  All food contains large quantities of phenylalanine so they need to be very restricted with the diet.  Remembering that everyone even those with PKU need a certain amount of phenylalanine.

Special products called protein substitutes have been developed and they contain little or no phenylalanine.  The dietician recommends the most appropriate one for the child.  These products contain extra Tyrosine and all the other amino acids needed for normal growth.  The amount required will be carefully calculated by the dieticians and doctors to meet the requirements.

Can The Diet Be Discontinued?

Basically there is no doubt that a child with PKU must continue with the strict diet throughout the developing years.  For teenagers and adults the advice is that there should be some restriction of phenylalanine throughout their life.

It was thought that the diet could be discontinued at around the age of 10-14.  Many older PKU teenagers and adults who have stopped the diet and eaten "normally" have been found to have had abnormal brain scans.  They are uncertain about the changes seen on these scans but there is the possibility that they are the result of the build up of the phenylalanine.  When the low phenylalanine diet was resumed some of the scans showed improvement.

Some adults with PKU have been found to have hand tremors, poor coordination abnormal hand and arm and leg movements.  The cause of this is unknown but it is most likely due to the high levels of phenylalanine found in the blood.  Older children and adults have reported they are much more able to think and concentrate more clearly when their blood levels are within normal range.  Some even say they feel as though they have cotton wool in their heads or like they’ve had a few to many.  For these reasons they do advise that the diet be kept to.

At present Tristan is having two Guthrie (heel prick) tests done a week, by myself or my partner.  We usually get the results 2 or 3 days later.  If his results come back too high we have to give him more formula, which is disgusting but Tristan seems to like it, he has rusks and wafer things prescribed to him, and eventually he’ll be given an open prescription which means anything he needs I just take a shopping list to his doctor and it will be prescribed for him.  It’s made me very aware of the amount of protein in foods not to mention other things.  Other than the protein content we have to make sure that there is no aspartame in the product as that also contains phenylalanine.  All in all other than his PKU he’s a healthy, happy "normal" (whatever that is) 7 month old boy.  As he gets older we don’t want to make a big thing of his diet as we want him to learn to control it himself and not to be ashamed of it as some people I’ve spoken to have said at times it can be shameful for them.

Everyone in this world is different in all ways, shapes and forms sometimes it’s good to be one of a few and personally doing the research it has made me appreciate how lucky I am to have such a loving family.

Some information taken from the NSPKU:  http://www.nspku.org

This is a members article by nighttalker