285 lines
12 KiB
Plaintext
285 lines
12 KiB
Plaintext
From: grx0644@uoft02.utoledo.edu
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A while back, there was alot of comments on PKU. Some comments were correct,
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some were just plain wrong. I decided to d/l an artical on PKU and post it for
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those interested.
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PHENYLKETONURIA (PKU)
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From the
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PEDIATRIC INFORMATION RESOURCE CENTER
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Rainbow Babies & Childrens Hospital
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2101 Adelbert Road
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Cleveland, Ohio 44106
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DEFINITION:
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Phenylketonuria (PKU) is a genetic disorder that is
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characterized by an inability of the body to utilize the
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essential amino acid, phenylalanine. Amino acids are the
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building blocks for body proteins. 'Essential' amino acids
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can only be obtained from the food we eat as our body does
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not normally produce them. In 'classic PKU', the enzyme
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that breaks down phenylalanine phenylalanine hydroxylase, is
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completely or nearly completely deficient. This enzyme
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normally converts phenylalanine to another amino acid,
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tyrosine. Without this enzyme, phenylalanine and its'
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breakdown chemicals from other enzyme routes, accumulate in
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the blood and body tissues. Although the term
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'hyperphenylalaninemia' strictly means elevated blood
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phenylalanine, it is usually used to describe a group of
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disorders other than classic PKU. These other disorders may
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be caused by a partial deficiency of the phenylalanine
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breakdown enzyme or the lack of another enzyme important to
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the processing of this amino acid. A normal blood
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phenylalanine level is about 1 mg/dl. In classic PKU,
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levels may range from 6 to 80mg/dl, but are usually greater
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than 30mg/dl. Levels are somewhat less in the other
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disorders of hyperphenylalaninemia. Chronically high levels
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of phenylalanine and some of its breakdown products can
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cause significant brain problems. Classic PKU is the most
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common cause of high levels of phenylalanine in the blood
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and will be the primary focus of this topic sheet.
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INCIDENCE:
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Classic PKU and the other causes of hyperphenylalaninemia
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affect about one of every 10,000 to 20,000 Caucasian or
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Oriental births. The incidence in African Americans is far
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less. These disorders are equally frequent in males and
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females.
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CAUSE:
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PKU and the other causes of hyperphenylalaninemia are
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inherited in a recessive fashion. This means an affected
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person inherited two traits for the disorder (e.s., one from
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each parent). A person with one trait for the disorder, is
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called a 'carrier' for PKU. Carriers do not have symptoms
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of the disorder.
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SYMPTOMS:
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Infants with PKU appear normal at birth. Many have blue
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eyes and fairer hair and skin than other family members.
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Currently, most symptoms of untreated PKU are avoided by
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newborn screening, early identification, and management.
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(see Treatment Section)
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The following describes untreated PKU symptoms-currently a
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rarity:
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About 50% of untreated infants have early symptoms, such as
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vomiting, irritability, an eczema-like rash, and a mousy
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odor to the urine. Some may also have subtle signs of
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nervous system function problems, such as increased muscle
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tone, and more active muscle tendon reflexes. Later, severe
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brain problems occur, such as mental retardation and
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seizures. Other commonly noted features in untreated
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children include: microcephaly (small head), prominent
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cheek and upper jaw bones with widely spaced teeth, poor
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development of tooth enamel, and decreased body growth.
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TREATMENT:
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Every state now screens the blood phenylalanine level of all
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newborns at about 3 days of age. This test is one of
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several newborn screening tests performed before or soon
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after discharge from the hospital. Usually, a few drops of
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blood are obtained by a small prick on the heel, placed on a
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card, and then sent for measurement. If the screening test
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is abnormal, other tests are needed to confirm or exclude
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PKU. Newborn screening allows early identification and
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early implementation of treatment.
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The goal of PKU treatment is to maintain the blood level of
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phenylalanine between 2 and 10 mg/dl. Some phenylalanine is
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needed for normal growth. This requires a diet that has
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some phenylalanine but in much lower amounts than normal.
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High protein foods, such as: meat, fish, poultry, eggs,
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cheese, milk, dried beans, and peas are avoided. Instead,
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measured amounts of cereals, starches, fruits, and
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vegetables, along with a milk substitute are usually
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recommended. Phenylalanine free formulas are available for
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all age groups. In some clinics, a phenylalanine
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'challenge' may be suggested to evaluate whether or not the
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child continues to require a low phenylalanine diet. This
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test identifies those few persons with a transient or
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'variant' form of the disorder. However, most authorities
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currently recommend lifelong dietary restriction of
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phenylalanine for individuals with classic PKU, in order to
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promote maximal development and cognitive abilities. Trying
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to reinstitute the PKU diet after a period of 'relaxation'
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to a regular diet, has been difficult for many individuals.
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Periodic phenylalanine blood level measurement, and the
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guidance of a nutritionist and other members of the health
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care team, allow individuals and families to work toward
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consistently maintaining the blood level in the desirable
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range.
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Fever and illness can cause normal body proteins to break
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down, the liberation of the body's own amino acids, and
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thus, a rise of the blood phenylalainine level. The
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physician and nutritionist can suggest dietary changes to
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help maintain levels in the desirable range during illness.
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Medical follow-up often involves periodic developmental
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screening. This checks for the expected normal development
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over time, and allows early recognition and intervention for
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problems.
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LIMITATIONS:
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None for treated individuals.
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COURSE:
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Maintaining phenylalanine blood levels in the recommended
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range maximizes the ability of individuals with PKU to reach
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their potential for normal development and lifespan.
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Authorities currently recommend that women with PKU who are
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of child bearing age, closely adhere to the low-
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phenylalanine diet and monitor phenylalanine levels before
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conception and throughout pregnancy. The risk of
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spontaneous abortion, mental retardation, microcephaly,
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and/or congenital heart disease in the child is high if
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Mother's blood phenylalanine is poorly controlled.
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BEHAVIORAL/EDUCATIONAL CONCERNS:
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The presence of a chronic condition may influence one's
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emotional development. In addition, lifestyle adjustments
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to accommodate more frequent doctor visits, and dietary
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restrictions may be required and impact day to day
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activities. These and other general issues are important to
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understand and are discussed in the accompanying topic sheet
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for "Chronic Illness".
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The following information addresses PKU specifically:
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Untreated PKU can cause significant brain problems including
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retarded mental development. Current screening for PKU in
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the newborn period has made unrecognized PKU a rare
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occurance. With good dietary control, the potential effects
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of PKU on development are minimized. However, recent
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studies indicate that loss of dietary control in childhood
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can interfere with cognitive development. These studies
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support the idea that individuals with PKU should maintain
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good dietary control throughout their lifetime. If problem
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areas in development are suspected, this should be shared
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with the parent so that an evaluation may be done and
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intervention can be instituted.
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It is important that all community personnel who work with
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individuals with PKU be aware of the dietary requirements
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and restrictions. The parent and/or nutritionist can
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suggest appropriate and allowable snack and mealtime foods
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outside the home. Supporting appropriate dietary habits,
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while minimizing attention to dietary differences is
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important. It is also important to be available to the
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individual should he or she wish to share concerns or
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feelings about being 'different' from peers. If persistent
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difficulty adhering to the dietary regimen is noted, the
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parent should be informed so that he/she and the medical
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team can address this issue further.
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Because blood phenylalanine levels are dependent on dietary
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control, insufficient phenylalanine intake may cause levels
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to be too low for growth and body functions. Low levels can
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cause mental and physical sluggishness, loss of appetite,
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anemia, rashes, and diarrhea. If these symptoms are
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suspected, the parent should be contacted and arrangements
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made for a physician evaluation.
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POTENTIAL EMERGENCIES:
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None.
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RESOURCES/REFERENCES:
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"Living with PKU" A publication from:
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Inherited Metabolic Diseases Clinic
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University of Colorado
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Health Sciences Center
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Denver, Colorado 80260
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Distributed by: Mead Johnson Nutritionals
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Evansville, Ill. 47721
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This booklet contains an extensive bibliography for parents
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and children with PKU.
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National PKU News
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7760 Ridge Drive N.E.
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Seattle, WA 98115
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Pediatric Endocrinology and Metabolism
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Rainbow Babies and Childrens Hospital
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Cleveland, Ohio 44106
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(216) 844-3661
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Dr. D. Kerr M.D. and Ms. J. McConnell - Nutritionist
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Provides medical evaluation and coordinates long term
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follow-up for children and families with PKU.
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Referrals to clinics in the Cleveland metropolitan area that are
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nearer to you may be obtained from your physician, Interlink at
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the Achievement Center for Children (216) 795-7100, or through
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Pediatric Endocrinology at Rainbow.
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Rudolph, A.M., Hoffman, JIE, Pediatrics, 18. Appleton and
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Lange, Norwalk, Conn., Los Altos, Calif. 1987, p. 239-242.
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Behrman, R.E., Vaughan, V.C. and Nelson, W.E., Pediatrics,
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13. W.B. Saunders, Philadelphia, PA. 1987, p. 280-282.
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Roh, F., Friedman, E.G., Koch, R.: Maternal PKU. Metabolic
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Currents. Vol I. No I: 1-8, 1988.
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Smith, I., Beasley, M.G., Wolff, OH, Ades, E.A.: Behavior
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Disturbance in 8-year-old children with early treated
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phenylketonuria. The Journal of Pediatrics, 112:403-408,
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March 1988.
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Seashore, M.R., and others: Loss of Intellectual Foundation
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in children with phenylketonuria After Relaxation of Dietary
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Phenylalanine Restriction. Pediatrics 75:226-232, February
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1985.
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Michals, K, and others: Return to Diet Therapy in Patients
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with Phenylketonuria. The Journal of Pediatrics, 106:933-
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936, June 1985.
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Holtzman, N.A., and others: Loss of Dietary Control in
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Phenylketonuria. The New England Journal of Medicine
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314:593-598, March 6, 1986.
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Information contained in this topic sheet from PIRC is available
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to the families and community personnel who care for children
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with special needs, with the intent to provide general topic
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information only. We strongly encourage direct contact with each
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child's physician for specific questions regarding care,
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medications, activity limitations and other concerns that may
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arise.
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PIRC is a service provided by Rainbow Babies and Childrens
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Hospital, funded by the following foundations:
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Bingham Foundation
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Cleveland Foundation
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George Gund Foundation
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Thomas White Foundation
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and NEC Computer INC.
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