phenylketonuria (1)

8/2/2019 PHENYLKETONURIA (1)

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Phenylketonuria is a rare condition inwhich a baby is born without the

ability to properly break down anamino acid called phenylalanine.

Deficiency of the enzyme

phenylalanine hydroxylase (PAH)leads to accumulation ofphenylalanine in body fluids.


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Phenylketonuria is inherited. Both parents must passon the defective gene in order for a baby to havethe condition. This is called an autosomal recessivetrait.


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Babies with PKU are missing an enzyme calledphenylalanine hydroxylase, which is needed tobreak down an essential amino acid calledphenylalanine.


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Without the enzyme, levels of phenylalanineand two closely-related substances build up

in the blood, this build up affects nerve

cells. These substances are harmful to the

central nervous system and cause brain

damage and mental retardation.

Phenylalanine has ketogenic and

gluconeogenic intermediates that contributeto the glucose pool, which can play a role

in normal brain development and function.


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PKU

PAH Deficiency

Phenylalanine Hydroxylase DeficiencyDisease

Follings Disease


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The most severe form of the disorder.

It occurs when phenylalanine

hydroxylase activity is severely reducedor absent.

People with untreated classic PKU have

levels of phenylalanine high enough tocause severe brain damage and otherserious medical problems.


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Mutations in the PAH gene that allow theenzyme to retain some activity result in

milder versions of this condition. Have a smaller risk of brain damage.

People with very mild cases may notrequire treatment with a low-phenylalanine diet.


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A woman who has PKU and becomespregnant.

Babies born to mothers with highphenylalanine levels may havecomplications at birth, most don'tactually inherit PKU and won't need tofollow a PKU diet after birth.


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Phenylalanine plays a role in the body'sproduction of melanin, the pigment

responsible for skin and hair color.Therefore, infants with the conditionoften have lighter skin, hair, and eyesthan brothers or sisters without the

disease.


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Other symptoms may include:

Delayed mental and social skills

Head size significantly below normal

Hyperactivity Jerking movements of the arms or legs

Mental retardation

Seizures

Skin rashes Tremors

Unusual positioning of hands


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If the condition is untreated or foodscontaining phenylalanine are not

avoided, a "mousy" or "musty" odor maybe detected on the breath and skin andin urine. The unusual odor is due to abuild up of phenylalanine substances in

the body.


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PKU can be easily detected with asimple blood test. The test is generally

done by taking a few drops of bloodfrom the baby before the baby leavesthe hospital.

If the initial screening test is positive,further blood and urine tests are requiredto confirm the diagnosis.


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The main treatment is a strict diet withvery limited intake of phenylalanine,which is mostly found in foods containingprotein.

Frequent blood tests will monitor PKUlevels as they change over time.

A supplement called neutral amino acidtherapy powder or tablets. Thissupplement may block some absorptionof phenylalanine.


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Follow a low-phenylalanine diet. Womenwith PKU can prevent birth defects by

sticking to or returning to a low-phenylalanine diet before becomingpregnant.

Consider genetic counseling. If you havea history of PKU, a close relative with PKUor a child with PKU, you may also benefitfrom preconception genetic counseling.


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A low Phe diet is used for treatment with,initially, the small amounts of Phe coming frombreast milk or commercial infant formula

considered sufficient intake in babies. In older children, protein intake is calculated

each day, whereby a child is allocated acertain number of grams or units of daily

protein, depending upon longitudinal plasmaPhe concentrations. Foods such as eggs, milk,cheese, meat, poultry, fish, dried beans andlegumes which are high in protein areexcluded from the diet.


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commercially available supplements ofessential amino acids, lacking Phe, need

to be taken on a daily basis. Childrenundergo regular blood Phe testingwhich, in concert with complete fooddiaries, are used by dieticians to make

adjustments to the recommended diets


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In the United States, about 1 in 15,000 birthsshow classical PKU.

In Turkey, 1 in 2600 births (Highest in the world)

The incidence is relatively high in Italy, China,and Yemen.

The gene defect occurs mainly in people fromEurope and the U.S.

The disorder is much less common in Asiansand Latinos.

Africa has the lowest rates of phenylketonuria.


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PKU is a treatable disease.

The outcome is expected to be very

good if the diet is closely followed,starting shortly after the child's birth.

If treatment is delayed or the conditionremains untreated, brain damage willoccur. School functioning may be mildlyimpaired.

phenylketonuria (1)

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