Phenylketonuria

PKU

PKU is a disorder caused by Recessive alleles.

The Disorder is found on the 12th chromosome

PKU Pedigree

How it is InheritedWhen a child is born with two copies of recessive alleles he inherits PKU

Boys and girls are equally at risk of inheriting this disorder.

Carriers are heterozygous for the trait

The disease affects at least one of every 16,000 babies, mostly those of northern European background. Jews, Asians, and Africans are less commonly affected.

In this condition, an amino acid called phenylalanine builds up in the bloodstream, causing brain damage.

In order for a child to inherit PKU, both parents must be PKU carriers.

Diagnosis

Nearly all cases of PKU in the United States are found in infant screenings

The Doctor or nurse draws a small sample of blood and then a Technician tests the blood to see if the trait is present on the 12th chromosome.

Symptoms

Mental Retardation

Behavioral and social problems

Seizures tremors or jerking movements

Rocking

Hyperactivity

Stunted Growth

Skin Rashes

Small head size

Vomiting

A musty odor in the skin, breath or urine caused by too much Phenylketonuria

The inability to change Phenylalanine Hydroxylase to Phenylalanine causes all of

these symptoms.

Treatment

A long life diet of a reduced protein diet is recommended to reduce build up of phenylalanine, but it can never be fully treated

Kuvan is the first FDA approved drug for treating PKU.

Life Expectancy

Although PKU is a life-long disease, people who have PKU have the same average life expectancy as those who do not have the disease.

Genetic counseling

Genetic counselors have limited advice they can offer to people with PKU.

Most genetic suggest a low or no protein diet depending on how sever the disease is.

They may also suggest a special formula that delivers the amino acids the body is deprived of due to PKU.

Interview• - How common is it that you deal with this disease?  PKU is not that uncommon as far as

genetic diseases go.  I dont know the exact incidence but you can look that up.  Most of the kids with PKU in houston are seen at our metabolic genetics clinic at TCH.

• -They are usually seen by the metabolic geneticist (MD), a metabolic nurse and a dietician. These specialists help coordinate their care and special dietary concerns and testing.

• -The diagnosis is almost always made on the newborn screening test.

• Sometimes the newborn screen is falsely abnormal which is why it is repeated and then a phenylalanine level is obtained.  If PKU is confirmed the baby is immediately started on the special diet.

• -Is this disease preventable by taking special precautions? The disease itself is not exactly preventable unless you do prenatal testing in a couple at risk.  However it is the bad effects of the disease that are completely preventable. 

• - Without the special diet and formula, people with PKU will have mental retardation.  If they stick with the diet, their intelligence is in normal range.

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3. How must people living with phenylketonuria modify parts of their lifestyle? The biggest lifestyle adjustment is diet.  It depends on their phe level, but most classic PKU kids can have NO protein!

Think about it, no cheese, no meat, no soda (look on the can). The diet is very restrictive and difficult to stick to as you can imagine. 

To supplement, people with PKU also have to drink a special formula so they can get essential amino acids that they dont get in their diet.  I have never tasted this personally but I have heard that it is nasty!

  You would think we could get it to taste good but no luck.  There are special companies that make foods like pasta and such for people with PKU also.  Frequent blood draws are also necessary to check Phe levels.

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• -What problems, if any, do people with phenylketonuria face later in life? Good question!  In the old days (10 years or so ago) we used to think that people with PKU could stop the diet when they reached adulthood (brain stops growing etc) however, many adults expressed difficulites when off diet.

• -They say they cant focus and have trouble with tasks and actually lose IQ points. So it seems the diet is important long term.  This is especially important for women. 

• -If a woman has PKU and becomes pregnant (off diet) her baby is at a very high risk to have mental retardation and other problems like very small head size. 

• -The baby does not have PKU but it is the effect of the high levels of phenylalanine in the mom's system that cross the placenta and hurt the baby.  So women with PKU should stay on the diet their whole lives and be especially vigilant when planning a pregnancy.

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• - Any other interesting facts about phenylketonuria?Other interesting facts:  There is a new treatment being tried out for PKU (sorry dont remember the name). 

• - Also for kids in Texas with PKU we hold a camp every summer called camp Phever.  It is held at Camp For All and is a collaboration between the genetics groups at Baylor/TCH and UT/Hermann. The kids love it.

Works CitedBatshaw, Mark L. "The Potential for Gene Therapy in Inborn Errors of Metabolism: A Case Example" Pkunews.org. 1999. National PKU News. 25 Jan. 2009

<http://www.pkunews.org/research/genether.htm>. Calvin College Hekman Library openURL resolver.Carter, Stien J. "Amino Acids and Proteins" Biology.clc.uc.edu. 1996. 25 Jan. 2009 <http://biology.clc.uc.edu/courses/bio104/protein.htm>. Furman, Patti. "Fw: Stratford Biology Project (Interview)." E-mail to the author. 22 Jan. 2009. Hull, Janet S. "Phenylketonuria (PKU) - Aspartame" Sweetpoison.com. 2002. Asparatame Detox Program. 25 Jan. 2009 <http://www.sweetpoison.com/phenylketonuria.html>."Phenylketonuria (PKU)" Mayoclinic.com. 2007. Mayo Clinic. 25 Jan. 2009 <http://www.mayoclinic.com/health/phenylketonuria/DS00514/DSECTION=symptoms>. Pku-info.org. 2006. 25 Jan. 2009 <http://fpwe.pku-info.org/index.php?id=16>.

"The Inborn Error of Metabolism in PKU." Pku.com. 2007. BioMarin Pharmaceutical Inc. 25 Jan. 2009 <http://www.pku.com/AboutPKU/TheScienceOfPKU.aspx>. "What is PKU?." Pkunetwork.org. Children's PKU Network. 25 Jan. 2009 <http://www.pkunetwork.org/PKU.html>.