Questions and Answers about PKU
By Virginia Schuett, MS, RD, Editor, National PKU News
I wanted to share a few of the hundreds of e-mail questions I have gotten from all over the world in the past year. The ones Iíve chosen to print are especially interesting and important. In some cases, my answers reflect my interpretation of what I have found in the medical literature. On several topics, other people may have more information than I do. I would be glad to hear of otherís experiences, or other scientific papers, especially those that relate to the controversial questions.
The following questions and answers were printed in the Fall 1997 issue of National PKU News.PKU & ADD/ADHD*
PKU, Depression & Anorexia
Treating Older Adults
PKU & Behavior Problems
Autism and PKU
* Also see report by Dr. Kevin Antshel under PKU Research titled ADHD and PKU, reproduced from the Winter 2008 issueAutism and PKU
A. There has been no causal relationship established between autism and vaccinations. Earlier research that suggested such a link has been found to be unreliable. No study since then has been able to establish a correlation. However, I believe there is a relationship between autism and PKU. Prior to newborn screening, 5% of children presenting with late-diagnosed PKU were first diagnosed as autistic. There is no question in my mind that those children improved on the phe-restricted diet. I have cared for quite a few such children, who are no longer autistic. Autism is a problem that has many causes. At the moment we think that it is a metabolic problem because it comes on gradually.Hyperphe, Mild or Atypical PKU and Classical PKU Clarified
A. While we now know there are over 500 different mutations in the phenylalanine hydroxylase gene causing PKU, it is still useful to roughly categorize PKU based on the amount of enzyme activity that is present, since the amount of enzyme activity influences blood level control and dietary phenylalanine tolerance.
Classification of PKU has been a difficult problem until mutations of the PKU
gene were identified. Most clinicians in the field utilize mutations and
tolerance to phenylalanine in the diet to identify and classify persons with
PKU. Newborn screening has been practiced worldwide since the l960s so that we
have many persons with PKU who have grown up and that has helped a great deal.
Dr. Charles Scriver in Montreal has categorized all recently identified
mutations and has published them on the internet so the information is readily
available to every one.
But actually, parents are more interested in the mutation that exists in their child or adult. Mutations are related to outcome and the interpretation I am going to give you is based on 50 years of experience. I use the data on mutations in the patients that I take care of to guide my therapy. Since I have been working with Drs. Savio Woo, Randy Eisensmith, and Flemming Guttler over the years (all of whom are involved in PKU mutation analysis), nearly all of my patients have had their mutations identified. The mutations that completely prevent activity of the enzyme that converts phenylalanine to tyrosine are considered severe. These patients usually have phenylalanine levels over 20 mg/dl (1200 Ķmoles/L). If each of the mutations carried by a person with PKU is severe then that person has the most severe form of PKU. These persons are considered to have "classic" PKU. Fortunately the phenylalanine restricted diet, when well managed and continued over a lifetime, protects the person from the devastating neurological damage exhibited by persons born before newborn screening.
If the person is fortunate and born with only one severe mutation and another that permits partial activity of the enzyme that can convert phenylalanine to tyrosine, the person has a less severe form of the disorder. If the diet is discontinued, that person may live for 20 to 30 years on a normal diet, but eventually will develop one or more of the complications seen in persons off-diet, such as mental illness, IQ decline, seizures, etc. Off-diet blood phenylalanine levels usually are between 15-20 mg/dl ( 900-1200 Ķmoles/L). These persons are considered to have mild or moderate PKU.
If a person is born with two mild mutations, the blood phe levels are much lower. Off-diet, they usually range from 4-15 mg/dl. These persons often do well without dietary treatment. There is disagreement among clinicians about how to treat these individuals. Some physicians treat anyone with a phe level over 10 mg/dl (600 Ķmoles/L) and some even treat those with a level of 6 mg/dl (360 Ķmoles/L). This latter group of patients will usually be sensitive to BH4 therapy; in the future, I believe they will all be treated when the FDA approves BH4 for use in PKU. These persons have had a variety of names applied to them, such as hyperphe, variant PKU, mild PKU, etc.PKU and Male Fertility
A. Seven years ago, Dr. Harvey Levy in Boston published a paper concerning fertility in PKU men and concluded that they were normal. However, Dr. Robert Fisch in Minneapolis published an article that suggested the sperm count was low in PKU men who were not on the diet. I know of no other studies that have been done in this area of research. If a PKU man is having difficulty with conception, I would suggest that diet treatment be resumed and I would bet money he would be virile.PKU Inheritance
A. Everyone has two #12 chromosomes. Each of the #12 chromosomes has one site for the PKU gene. A carrier of PKU has a mutation on one of the #12 chromosomes. If a carrier marries another carrier (who also has a mutation on the #12 chromosome, there is a one in four chance at each pregnancy that their child will inherit two mutant PKU genes, one from each parent. There is a two in four chance at each pregnancy that the child will be a carrier for PKU and a one in four chance that the child will be completely free of the mutation. These are the mathematical probabilities only. In a real family, there may be two or three or more children with PKU. Other carriers may have children and none of their children have PKU so they never know they are carriers. As soon as a child with PKU is born, you automatically know that both parents have a mutation that the child inherited.PKU Carrier Determination
A. The only accurate way to determine if a person is a carrier is to have a DNA analysis done to identify the mutation. This is a very expensive test, around $1000 or more, and is only done in a few places in the world. These include Montreal Childrenís Hospital in Montreal, Quebec, Canada (www.moleculargenetics.mcgill.ca); The John F. Kennedy Institute in Glostrup, Denmark (firstname.lastname@example.org, the web site www.kisoe.org); and the Childrenís National Medical Center in Washington, D.C. (email@example.com, the web site http://www.cnmc.org). There also is a "loading" test, but it is only 90% accurate and I donít recommend it.Incidence of PKU in Other Countries
A. The incidence of PKU in Caucasians is about 1 in 10,000. In African Americans it is 1 in 200,000. So the doctors are correct, it is quite unusual in African Americans. In Chinese, it is 1 in 15,000, in Japan it is 1 in 100,000. In Turkey, it is 1 in 2500 due to intermarriage. In Ireland it is 1 in 4,000. In Poland, it is 1 in 7,000. You can see it varies a great deal throughout the world.Low Protein Diet and Hair Falling Out
A. Your hair is falling out because your protein intake is too low (too little PKU formula). We see this commonly in patients who are not well-monitored. Have your doctor measure your blood total protein and A/G ratio. Iíll bet they are both low. See your dietitian for advice on formula.PKU and Aggression
A. This behavior suggests to me that you are either off the diet, or if you are on the diet that your blood phe levels are too high. PKU patients who are off diet or whose levels are too high are often aggressive and less stable.PKU and Arm Twitching
A. I am almost certain that your neurological symptoms are due to phenylalanine toxicity because of your high levels. You should resume diet treatment before the symptoms get worse. A PKU clinic needs to give you guidance.Vomiting PKU Formula
A. The reason for the regurgitation is usually due to taking the product on an empty stomach. It is more therapeutic to give smaller amounts of the formula more frequently, with meals and snacks.PKU Formula and Headaches
A. This usually occurs if the person drinks the formula on an empty stomach. Have your son take the formula with a meal or snack and see if that doesnít stop the problem.PKU and Agoraphobia
A. The high phenylalanine in your blood is blocking the transport of tyrosine and tryptophan into your brain. This results in a deficiency of dopamine and serotonin in your brain, causing your agoraphobia, depression, and panic attackes. Psychotropic drugs will help, but the therapeutic approach is to resume the phenylalanine-restricted diet.PKU and Eczema
A. When the phe level is elevated, the child is more likely to have eczema. The phenylacetic acid that is formed from the breakdown of phenylalanine is irritating to the skin. Eczema is a very common problem in untreated PKU and almost always disappears when the diet is started.PKU and Babies Spitting Up
A. Your baby has pyloriospasm. This is not an unusual pediatric disorder and it is not associated with PKU. In actuality, it is easily diagnosed by an upper GI series. You are doing the right thing by consulting your doctor.PKU Diet and Fatty Acid Deficiency
A. Your research pointed you in the right direction. The bumps under your eyes could be caused by a lack of long chain fatty acids. You should try to always use oil in cooking and in salad dressings. Canola oil is the best source of the essential fatty acids, particularly omega-3 and omega-6 fatty acids. Two tablespoons a day of canola oil is all you need. You also can take fish oil capsules, which may contain flax oil, another source of essential fatty acids. You can purchase these at local drug stores. Besides Phlexy-10, the amino acid blends and formula bars also do not contain essential fatty acids and they must be supplemented with dietary sources. Bumps under the eyes can also be a symptom of a more serious problem with cholesterol metabolism and people with such bumps should be seen by a doctor.PKU and ADD/ADHD
A. Yes, I agree. It is certainly possible. Furthermore, I think ADD is uncommon in well-treated PKU patients.PKU Diet and Protein Deficiency
A. You are correct. Your daughter should take all of her prescribed formula. She could develop a protein deficiency otherwise. Also, allergies are much more common in PKU people who are not taking adequate formula.Phenylalanine Content of Aspartame
A. One gram of aspartame equals 1,000 milligrams aspartame. Approximately half of the aspartame molecule is phenylalanine. Therefore, an estimate is that one gram aspartame would contain approximately 500 milligrams of phenylalanine. If a label states the amount of aspartame, you can do estimates based on this formula. Of course, people with PKU on the diet should try to avoid eating foods and consuming medicines that contain aspartame.PKU and Lack of Energy
A. Is your son taking a daily vitamin/mineral supplement? If his blood phe levels are between 2 and 6 mg/dl and his caloric intake is adequate for normal weight, a lack of vitamins and minerals (such as iron) is usually the reason for lack of energy.PKU & ADD/ADHD
A. Some parents and professionals have believed for a long time that there is a relationship between elevated phe levels and ADHD (Attention and Hyperactivity Disorder) and ADD (Attention Deficit Disorder), based on their own experience. At a parents meeting several years ago, I remember a question was asked of the audience about how many parents had children diagnosed with ADD or ADHD. More people raised their hands than we would have expected in that size population. Several newer papers in the medical literature do seem to suggest there is an increased incidence of attention problems in children with PKU. For example:
We do know that persons with untreated PKU tend to be very hyperactive, restless people unable to focus on tasks. For early treated children with PKU, the evidence for increased incidence of attention problems is still sketchy and an area for further research. But the little we do know about this again strongly suggests that consistently low blood phe levels are the most prudent.
A. There are several reports in the medical literature that suggest a relationship between high phe levels and depression. For example:
It is known that high phe levels decrease production of a key neurotransmitter important for mood maintenance, serotonin. Many antidepressant drugs act by elevating serotonin. It is thus natural to suspect that depression could be a consequence of high phe levels. There is only one reported case of PKU and anorexia, although the relationship between the two, if any, is unclear (Clarke, D.J., and Yapa, P., J. Mental Defic. Res. 35: 165-170, 1991.) This is the case of a girl with late-treated PKU and mild mental retardation who developed severe behavior disorders and anorexia in her teens. Her anorexic symptoms did not respond to the usual management strategies, but did respond to a reduction of serum phe after the introduction of a low protein diet. Although her phe levels were never lowered to a good control range on a modified low protein diet (she refused a low phe diet that included the PKU medical food), this suggests a connection between high serum phe levels and the development of anorexia.
So in your sisterís case, anorexia may be another sign of disturbed mental processes caused by high blood phe levels.Treating Older Adults
A. To answer this and the many similar inquiries I get regarding previously untreated adults: I believe that diet treatment is always worth a try in older adults, if the facilities and support are available. It has been shown often that lowering blood phe levels can led to improvements in behavior, eczema, and a variety of other problems. While the diet cannot undo the brain damage that has been done, it can allow the adult to learn more easily due to better and more focused behavior. Please see the Diet Intervention Guidelines for Adults with Previously Untreated PKU in the Adults with PKU section of the Web site. These are practical guidelines for diet treatment based on experiences with several adults who were placed on diet for the first time in their 50's.PKU & Behavior Problems
A. Based on reports I have heard from families, I do think it is possible that intermittent higher levels can cause behavior changes. It seems that some children are more sensitive to higher phe levels than others. But for any one child, it is hard to say. The important thing is to try to control her diet very consistently, whether before a blood test or not, and to get frequent blood tests done. When the phe level comes back, you can then presume that for most of the interim time, her level was in the general vicinity of that number. (This is a valid assumption unless of course she is sick, or unless something else unusual is going on with her growth or other factors that would significantly affect her phe level.) If the phe level is low (in the range of 2-6 mg/dl), you are probably just experiencing a very normal three-year old.
Last update: February 2008
National PKU News: www.pkunews.org