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Facts for now
Facts for the future
By Linda A. Gleason, MS, RD
© University of Wisconsin-Madison 2000
For Know to Grow Session D1
Phe Facts of Life
You have PKU because you were born with it.
Your parents each carry one gene for PKU.
Because they also have one working gene
they don’t have PKU.
They are carriers.
By chance, they each passed on a PKU gene to you.
You have two genes for PKU and no working genes.
So you have PKU.
It was a 1 in 15,000
chance that you
would have PKU!
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You may have brothers or sisters who don’t have PKU.
That is because one of two things happened by chance.
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Either
one of your parents passed on a PKU gene
and the other passed on a working gene.
In which case your brother or sister would be a carrier.
Or
both of your parents passed on the working gene.
If your siblings don’t have PKU no one knows which case happened.
Carrier
OR
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Looking way ahead, having PKU does not mean your kids will have PKU.
In fact, they probably won’t. It’s about a one in one hundred chance
that you would marry a carrier and both pass on the PKU gene.
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Non-carrier
Facts about PHE
Phenylalanine is called “Phe” for short.
Phe comes from the food you eat. It is one part of protein.
Phe is one of
20 amino
acids found
in food
proteins.
phe
phe
phe
Protein is like a long chain made up of small pieces called amino acids.
Phe is one
of those
amino
acids.
Because phe is part of protein, foods with lots of protein have lots of phe.
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When you eat foods with protein your body breaks it apart into amino acids.
phe
phe
Then your body uses the amino acids to build new body proteins
like muscles.
Everybody
does!
You need body proteins to grow and work.
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Facts about Enzymes and Phe
A working gene makes an enzyme.
Enzymes help change amino acids in your body.
Enzyme
An amino acid is changed to a different amino acid by an enzyme.
If there is no enzyme to drive these changes, amino acids build up to unsafe levels.
In PKU, phe is the amino acid that is not getting changed.
This happens because a liver enzyme is not working.
Phe builds up to dangerous levels.
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Facts about Phe and Food
In someone who doesn’t have PKU, it’s OK if they eat lots of phe.
Phe from
food
1st phe goes to make body proteins.
phe
phe
phe
phe
1st
1st
phe
phe
phe
phe
2nd
phe
1st
enzyme
tyr
2nd phe is changed to tyrosine by a liver
enzyme.
All of the phe gets used up.
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You have PKU so your body uses phe like this…
Your body breaks apart the protein into amino acids.
Your body uses those amino acids, including phe, to build body proteins.
Here’s the difference--Your body cannot change any extra phe to tyrosine because the enzyme is not working.
Your body cannot handle any extra phe.
This is just like
Your body cannot make tyrosine.
everyone else.
1st phe goes to make body proteins
Phe from food
phe
phe
1st
phe
phe
phe
phe
This is not like
everyone else.
1st
phe
phe
phe
2nd
1st
phe
phe
phe
phe builds up
phe
phe
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phe
cannot
be
changed
to
tyrosine
tyrosine
Facts about Too Much Phe
Like we said, your body cannot handle too much phe.
When you were a baby high phe levels were extremely dangerous.
Babies with very high phe levels grow to be mentally retarded.
Some clinics differ, but
high levels are blood phe
levels over 10 mg/dl.
High phe levels are still harmful to you now.
High phe levels still affect your brain.
You won’t be retarded but here’s what happens…
You may have
heard of older
kids going off
the diet.
Clinics used to
think that after
age 6 phe would
not hurt your
brain.
Now we know
differently.
Many kids with PKU who have high phe levels over a period of time don’t do as well in school.
This could be because high phe levels:  make it harder to concentrate
 make it harder to remember
 make it harder to plan and organize your work
High phe levels change the
way your brain looks on special
x-rays. We don’t know what
this means yet, but the brain
changes are obvious.
Kids complain of being
more irritable and moody
when their levels are high.
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Facts about High Phe Levels and Pregnancy
It is possible for young women with PKU to have healthy babies when they keep their
blood phe levels between 2-6 mg/dl for the whole pregnancy.
This is hard work for the mother-to-be.
She has to follow her diet exactly.
But the results are worth it--a healthy baby.
Babies whose mothers have phe levels greater than
6 mg/dl may have babies with severe problems.
The babies are born smaller than expected with small heads.
The babies do not develop normally.
Some of the babies have life-threatening heart problems.
The clinic will work closely with all young women, when that time comes,
to help them have a healthy baby.
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It’s like
walking a
tight rope.
Facts about Phe and Diet
You need some phe to grow and work but too much phe is harmful.
The answer to this balancing act is the diet for PKU.
The diet gives you the right amount of phe from foods that are low in protein.
1 apple
4 pieces low pro bread
butter and jelly
20 Bugles
1 package of fruit snacks
12 mini carrots
½ hot dog
110 mg phe
110 mg phe
Phe balance
High protein foods have way too much phe
to eat an amount that would be at all satisfying.
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Amazing!
All this food has
the same amount
of phe as
½ of a hot dog!
Facts about Formula
By following the diet for PKU, you eat foods that are low
in protein to give you just the right amount of phe.
 Energy to help you go
 Nutrients to help you grow
 Helps to keep your levels low
Just drink it!
You still need all the other amino acids in protein so your
body can build proteins.
You would not get enough of the other amino acids
by eating only foods that are low in protein.
That’s where the PKU formula comes in.
It provides all the other amino acids found in food protein--without the phe.
The formula also contains vitamins, minerals and
nutrients that give you energy.
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You get protein and
tyrosine from a PKU
formula.
It has no phe.
Facts about What It Takes
Having phe levels that are safe takes-- planning and keeping track of your diet
 working with your parents and the people at the PKU clinic
 finding some good friends you can talk to about all of this
 keeping up on the latest about PKU in the National PKU News or checking out the
web site at: www.pkunews.org
It’s hard, but it’s worth it!
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