Introduction


Phenylketonuria(PKU) is an inherited disorder in which the body is unable to breakdown an amino acid called phenylalanine. This causes the amino acid to build up in the body of affected individuals. High levels of phenylalanine can be detrimental and toxic to the body. People with PKU have to follow a strict diet in order to prevent the build up of large amounts of phenylalanine in the body. 

Two types of PKU: (1)classical and (2)variant PKU. Classical PKU is the more severe type of PKU as children can get permanent brain damage if left untreated. The variant PKU is the less severe form as they have a lower risk of brain damage but they still need to follow the strict PKU diet.

Causes of PKU

PKU is due to mutation in the Phenylalanine Hydroxylase(PAH) gene. Both parents must pass down a copy of the mutated gene for their child to develop the condition. If only one parent has the PKU gene, the child is a PKU carrier. Therefore, it is an autosomal recessive trait.


The function of the PAH gene is to provide information for the production of an enzyme called phenylalanine hydroxylase. This enzyme converts phenylalanine to other important substances in the body.

The gene defect occurs mainly in people from Europe and the U.S. It is less common in Asians and Latinos. Africa has the lowest rates of PKU.

Mothers who have PKU but refuse to follow the recommended diet during pregnancy may affect their unborn child due to accumulation of phenylalanine in the mother's blood.

Detection Test


  1. Blood phenylalanine: Tested by chromatography but Tandem Mass Spectroscopy is more relaible but expensive. Normal level is 1mg/dl but in PKU, level is more than 20mg/dl.
  2. Guthrie Test (shown in the picture above): Also known as Neonatal Heel Pricking and it is a rapid screening test. Uses Bacillus subtilis that requires phenylalanine as a growth factor. This bacteria will be spread on a specially-prepared agar and small disc containing the infant's blood will be placed on the agar. If there is presence of phenylalanine, this compound will diffuse into the agar and promote the growth of the bacteria.
  3. Ferric Chloride Test: Ferric chloride is added to the patient's urine containing phenylketones. Transient blue-green colour will indicate that the patient is positive for PKU. However, this method is less reliable.

Symptoms



Some symptoms of PKU in newborns and older children are:
  • Mental retardation
  • Behavioral or social problems
  • Seizures, tremors or jerking movements in the arms and legs
  • Hyperactivity
  • Stunted growth
  • Skin rashes (Eczema)
  • Small head size (Microcephaly)
  • A musty odor in the child's breath, skin or urine, caused by too much phenylalanine in the body
  • Fair skin and blue eyes, because phenylalanine cannot transform into melanin — the pigment responsible for hair and skin tone

Metabolism



Normally, our body will breakdown phenylalanine to tyrosine which will then form catecholamine (Hormone such as dopamine formed in the adrenal gland), melanin and other hormones. This is usually the main route of phenylalanine while the minor route is the transamination to phenylpyruvate, which will be subsequently metabolized.

Hydroxylation of phenylalanine
The enzyme catalyzing the reaction is phenylalanine hydroxylase (PAH), a mixed-function mono-oxygenase that uses molecular oxygen.  This enzyme also uses the cofactor tetrahydrobiopterin (BH4), which is oxidized in the course of the reaction to dihydrobiopterin (BH2).  The cofactor must be regenerated by a separate system of enzymes for PAH action to continue.
Native PAH is a polymeric enzyme; it is not yet clear if the subunits are identical, but SDS-polyacrylamide electrophoresis shows two 50kDa subunit bands.  However, there is only one genetic locus for PAH.

Transamination of Amino Acids

Transaminases catalyze the transfer of -NH2 groups from the amino acids, onto alpha-ketoglutarate.  Many different transaminases are known, and they are generally of broad specificity for amino acids (that is, one enzyme can accept as substrates two or more different amino acids).  All have the same cofactor requirement - pyridoxal phosphate (vitamin B6).
Transamination of phenylalanine to phenylpyruvate is normally of negligible importance, so long as the main route is functioning. However, if the main route is blocked for some reason, then transamination of Phe becomes quite important. In fact, the production of the distinctive minor metabolite, phenylpyruvate, can be used to diagnose deficiencies in the main route of metabolism of phenylalanine.


Abnormal Metabolism
Under hyperphenylalanine conditions, where there is too much phenylalanine in the body, the body will resort to convert the phenylalanine through the transamination pathway, converting phenylalanine to phenylpyruvate.





The role of alpha-ketoglutarate as the acceptor of the amino group from Phe, with consequent formation of glutamate.

The phenylpyruvate is further metabolized. Decarboxylation of phenylpyruvate gives phenylacetate, while a reduction reaction gives phenyllactate.  The phenylacetate can be further conjugated with glutamine to give phenylacetyl glutamine. All of these metabolites can be detected in serum and urine by suitable clinical tests. 



When the body constantly uses this pathway, there will be a buildup in these metabolites, which can be harmful and toxic to the body.


Overview of Phenylalanine Metabolic Pathway in PKU.

Treatment



SPECIAL PKU DIET
Affected individuals should avoid foods high in protein such as:
·         Chicken
·         Milk
·         Cheese
·         Meat
·         Fish
·         Soya Beans
·         Pork
·         Chocolate
·         Nuts
·         Beans
·         Beer

Foods that have aspartame, artificial sweetener, should be avoided such as diet sodas as aspartame releases phenylalanine when digested.

Even low protein food such as fruits, vegetables and desserts should be limited.

A diet with low-protein rice, pasta and cracker is usually recommended for with PKU.

Newborns that have PKU are still able to get their daily requirements through a special formula, made especially for babies with PKU, which is phenylalanine-free since they are unable to drink breast milk as well as regular infant formula which have phenylalanine. For older children and adults, they too are able to take a special protein powder supplement which is, of course, phenylalanine-free. It should be divided between meals.

Life with 2 PKU children

Rare genetic disorder leads Holladay family to healthy eating habits


By Deseret News

Published: Sunday, Dec. 2 2012 5:28 p.m. MST
Seth Oliver, 3, has a banana for a snack while his mother has her pen ready to jot it down in his notebook at their Holladay home Friday, Nov. 30, 2012.

HOLLADAY — Making sure kids eat their vegetables is hard enough for some moms, but watching, weighing and measuring every morsel of everything they eat is another story.
"I know every bite of food my kids have eaten, every day of their lives," said Amy Oliver, a Holladay mother of three and part-time attorney. Two of her kids require extra attention, but one wouldn't know it just by looking at them.
"The only way you can tell is if you watched them eat, and even then, if you watched carefully," she said.
Claire, 5, and 3-year-old Seth Oliver have phenylketonuria, or PKU, a rare genetic disorder that affects a person's ability to process an important part of protein called phenylalanine. They are two of about 92 children and hundreds of adults in Utah who are diagnosed with the very rare condition, which requires scrupulous note taking on the only known treatment — a special diet for life.
Over the years, Oliver has grown accustomed to subtracting the weight of the small, color-coded plastic dishes she uses to serve the kids, the leftover peels from various foods, and whatever food her children don't eat, all the while meticulously calculating the results to get the amount of protein each child has received each day.
Claire and Seth each need about 22 grams of protein, or 1,500 milligrams of "phe" each day in order to be healthy. The amount won't change much as they get older or as they grow bigger, but it has to be monitored to prevent dangerous side effects, including irreversible brain damage and behavioural issues.
Oliver and her husband have an older son, Luke, who didn't receive the mutant gene from each of his parents and therefore can eat a normal diet.
One in 50 adults are carriers of PKU, and every person carries up to 50 defective genes that could be passed on to their children, said Dr. Nicola Longo, a professor and the chief of the division of medical genetics at the University of Utah.
There's a one in 2,500 chance that two adults who each carry the gene will come together to have a child with the metabolic disorder, and the odds are one in four for each pregnancy, he said. One in 15,000 children are born with the condition, and it is typically caught within the first week of life.
Newborn screening, in which a tiny amount of blood is drawn from the heel of a baby, checks not only for PKU, but for about 37 other metabolic disorders. The two-test series is less than $100 but critical for proper development, Longo said.
"If you find out later, the child might be dead or have irreversible mental disabilities," he said. "If you wait for symptoms, it is just too late."
Symptoms are evidenced in delayed achievement of normal developmental milestones, as the brain fails to grow. Delayed diagnosis and treatment can lead to mental retardation and other neurological problems, such as memory loss and mood disorders.
Longo said newborn screening — the first test of which is performed within 72 hours of birth, and the second between 7 and 21 days of age — has been conducted in the United States and Europe for the past 40 or more years. It was initiated in 1963 and mandated by law in the U.S. in 2008. Unless parents opt out, it is routinely conducted, saving lives and brain function, Longo said.
He said, however, there are still patients who are diagnosed later in life with PKU after mental disabilities arise because they were not diagnosed at birth.  Those individuals, Longo said, are often institutionalized and cannot live normal lives.
Adults who do not follow the stringent diet can slip mentally, including loss of various executive functions. Longo said the effects are reversible if a person returns to the diet, but that is easier said than done.
"They often do not realize they are experiencing problems, and if they do not know, they cannot fix it," he said. "They end up having problems doing their jobs, with relationships, but they can still live relatively normal lives. It is just harder to do so."
The Oliver children are learning as they grow, and so far, they don't know any different.
Claire knows she can only eat "low-phe" foods, and the family tries to incorporate as much of the kids' diet into their daily lives, "recognizing it is always going to be different," Oliver said.
She's lost her own taste for meat, and the whole family eats a lot healthier, she said.
Most of the children's meals have to be homemade, aside from the occasional frozen vegetables that can be warmed in the microwave.
"There are no convenience foods for us," Oliver said.
She often uses Metamucil to give bread made with rice flour added bulk and fiber. The kids are allowed minimal spices and flavorings, but they enjoy a little bit of butter on otherwise bland mashed potatoes.
To make up for the lack of protein needed for optimal growth, Claire and Seth, and other patients of PKU, have to drink special formula, a synthetic milk product that has phenylalanine removed. The formula can cost a family up to $12,000 a year, but in Utah, it's mandated to be covered on most insurances, said Oliver, who started a local support group called the Intermountain PKU and Allied Disorders Association in 2008.
"As a mother, the most reassuring thing is to see other kids with PKU running around, being normal kids," she said. "It's also nice to be able to talk to other mothers about what we go through."
In addition to raising awareness and fundraising for research, the association initiates parents of newly diagnosed PKU patients with a starter kit containing a food scale, calculator, cookbook and various other resources, which Oliver said quickly become the tools of the trade, as they go everywhere with parents of children with PKU.
"You have to be really organized," she said. "We never do anything spur of the moment, and we carry supplies with us everywhere we go."
A typical day includes measured amounts of a variety of fruits and vegetables, crackers, low-protein cheese, popcorn and no meat, dairy, eggs, beans or nuts, which are forbidden on the special diet.
"You don't want any of your children to have a health condition of something they have to deal with for the rest of their lives, but the silver lining is that they have each other in this," Oliver said.
Claire and Seth are closely monitored by geneticists at the U., who follow their growth and development, but also their dietary needs, which can change over time.
Oliver admits the diagnosis was daunting at first, but "if it's your child's life on the line, you could do anything for them," she said.
"We're just like anybody else. We just eat differently. We eat to live. We view food as a necessity," Oliver said.
A growing understanding of food issues in the general public, including gluten intolerance and various allergies, have made the family feel more at home when they go out, and explaining their sometimes awkward habits of weighing and measuring foods gets easier as they go.
"They know they can't eat anything without clearing it with us first," Oliver said, as she sliced an apple Seth picked from the large fruit basket poised on the kitchen counter.
It's nice, she said, that they want to eat healthy foods, but it is also comforting for her, knowing that they have to in order to thrive.

New treatment discovered!

New Options For People With PKU

Apr. 7, 2009 — For people with the genetic condition known as phenylketonuria (PKU), diet is a constant struggle. They can eat virtually no protein, and instead get their daily dose of this key macronutrient by drinking a bitter-tasting formula of amino acids. Yet drink it they must; deviating from this strict dietary regimen puts them at risk of developing permanent neurological damage.
In the near future, fortunately, a better option may become available.
In April, a team of University of Wisconsin-Madison researchers will publish the second of two key papers showing that a unique protein derived from whey — known as glycomacropeptide, or GMP — is safe for people with PKU to eat. GMP is the first known natural protein that is safe for this group, and these findings are poised to revolutionize the PKU diet. Already, Cambrooke Foods, a Massachusetts company that specializes in the manufacture of medical foods, is in the process of developing GMP-fortified snack foods for commercial sale.
"It's so important to individuals on the PKU diet to have new options, to have their diet liberalized. It's a quality-of-life issue," says Denise Ney, a professor of nutritional sciences who led the two studies. "Adolescents have an especially difficult time [staying on the diet], but it's so critical that they do."
People with PKU are born without the enzyme responsible for breaking down phenylalanine, one of the 20 major amino acids that form the proteins we eat in everyday foods. While small amounts of phenylalanine are essential for PKU patients, excess amounts stay in their bodies indefinitely and interfere with brain function. Those who go off-diet often suffer from concentration problems and depression. Some even sustain permanent brain damage. The GMP protein isolated from whey, on the other hand, is the only known dietary protein that contains only trace amounts of phenylalanine; absolutely pure GMP, in fact, is completely phenylalanine-free.
The first GMP human feeding trial was published in February in the Journal of Inherited Metabolic Disorders. In it, Ney and her team describe the experience of an individual with PKU who volunteered to consume an all-GMP diet for 10 weeks. As the paper explains, not only did the subject enjoy the GMP-fortified snack bar, pudding and sports beverage that supplied most of his daily protein, but the amount of phenylalanine in his blood actually starting going down after he ate these items for a couple of weeks.
"And because the subject enjoyed the GMP foods, he was more inclined to eat them throughout the day, which helps keep the body's protein metabolism running efficiently all day long," says Ney. "When he went back to the amino acid formula, he went back to drinking it all in one sitting."
Ney's new study, published in the April issue of the American Journal of Clinical Nutrition and appearing online on Feb. 25, describes an 11-person trial of shorter duration involving PKU patients receiving care from UW-Madison's Waisman Center who agreed to spend six days at the University Hospital's Clinical and Translational Research Core. In the study, subjects adhered to the amino acid formula diet for four days, and then switched to the GMP diet for the following four. (Subjects spent the first two days of the study at home.) In the end, no adverse health problems were found, and 10 of 11 subjects claimed to prefer the GMP diet, making the bottom line of this study the same as the first — that GMP is safe and acceptable.
In this shorter study, variations were seen among individual subjects, but the overall blood phenylalanine levels measured after meals were comparable in the two diets. Additionally, the GMP diet improved protein metabolism compared to the amino acid formula.
Members of the PKU community have been eagerly monitoring the progress of this research project for nearly a decade, since UW-Madison food engineer Mark Etzel published a key paper describing how to isolate GMP from whey. A few years ago, when things got to the point of starting human feeding trials, the researchers discovered they already had a long list of eager volunteers, including Matt Cortright of Wausau, Wisconsin, who developed seizures and other problems after abandoning the amino acid formula for a few years during early adulthood.
"The main reason I helped out with this study was so that newer generations won't have to go through the things I have. It makes me happy to see how far the studies have come since I was younger, and the choices future generations will have," writes Cortright, now 32, in a letter to Ney. "I just hope that I will also have the opportunity to use these [GMP food] products [in my own daily life] as well."