Causes And Treatments: What Is Phenylketonuria (Pku)?

Phenylketonuria, or PKU for short, is a relatively rare hereditary disorder that produces the inability to digest phenylalanine, a naturally occuring amino acid.

Phenylketonuria (PKU) is a relatively uncommon genetic condition that results in an individual's inability to process a certain amino acid, called phenylalanine. It is an autosomal recessive gene, meaning it must be passed to a child from both parents in order to occur. This means that if you and your partner both have the condition, it will surely result in a child with the condition; if you both have the recessive gene, but don't display symptoms, you have a 25% chance of passing it on. If one of you shows symptoms or has the recessive gene and the other has neither, then there is no chance of passage. All this accords to basic genetic principle, but it should be clear that the rarity of the defect is rather extreme. It occurs in only one of every 14,000 to 20,000 live births, by best estimate, being most common in those of Caucasian and Native American descent, and least in those of African American, Asian and Hispanic descent.

Amino acids are the body's protein building-blocks, tiny molecule chains that combine in different orders and amounts to produce the basis of life, the protein. When one digests protein, it is broken down into its component amino acids, and these amino acids are often broken down yet again to produce the building blocks of more amino acids for energy and for reorganization into other proteins. In most individuals, the enzyme phenylalaine hydroxylase (PAH) is able to process the phenylalanine amino acid normally when it's derived from protein, but this enzyme is lacking in those with PKU. The buildup of phenylalanine in the bloodstream can be severely detrimental to the body, and will most permanently affect the mental development of the victim.

Every newborn in the United States and most other industrialized nations is checked for PKU at birth as a part of their routine blood test. This usually occurs by the second or third day of life, as the test measures levels of phenylalanine in the blood, and it may take a little while for these levels to build up to easily measurable quantities.



Early-onset symptoms include an unusual, musty odor about the infant, especially to the urine, hair and skin, which may be especially itchy or dry. Digestive difficulties usually accompany the disorder, and severe vomiting and diarrhea may occur. An unusual sensitivity to light is commmon, as well.

Treatment consists of permanent diet modification. High-protein diets are exceptionally rich in phenylalanine, and consuming products with large quantities of protein can cause permanent brain and nervous damage to one afflicted with the condition. This includes milk and formula. Phenylalanine-free formula should be used early in life, and protein shakes specially designed to be free of the amino acid should be used as a supplementary protein source later in life. Failure to adapt one's diet to this reduced-protein regimen at any point may cause potentially permanent nervous damage, noted by a notable drop in intelligence quotient. Mental retardation can occur as a result of non-treatment early in life. Early treatment should begin as soon as the condition is recognized, but it especially important that they begin within the first three weeks of life, before the damage is done.

Aspartame, known often as Nutrasweet or Equal, contains phenylalanine. Those with PKU may not consume diet drinks or any product containing aspartame. This does not mean the sweetener is dangerous to individuals without PKU any more than meat, milk or beans. Regular blood testing, performed about biweekly, should be performed on children with the condition. Tests may be reduced to about once a month after an individual reaches adulthood.

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