Topics: Phenylketonuria, Phenylalanine, Mental retardation Pages: 6 (2145 words) Published: April 23, 2013
Phenylketonuria is described as a metabolic genetic disorder. This disorder is characterized by the lack of production of the enzyme phenylalanine hydroxylase. This enzyme is used to break down the amino acid phenylalanine into tyrosine. Without this enzyme, the body cannot break down and waster phenylalanine, therefore it accumulates in the bloodstream. This accumulation of phenylalanine in the blood can spread to the brain and create a toxic effect. This paper is to describe, in detail, some of the pathophysiological facts of phenylketonuria. Phenylketonuria is a genetic disorder, so it is spread through genes. This disorder is described as an autosomal recessive disorder. This means that two copies of the abnormal gene must be present for the disorder to manifest. If a person has only one mutated gene, this means that the person is a carrier of the gene and could pass it on to their children. If both parents carry the gene, this means that their offspring have a 1 in 4 chance of having the disorder, and a 1 in 2 chance. This means that if the mother has the mutated gene and the father has the mutated gene, their offspring has 25% chance of having the disorder and a 50% chance of passing the mutated gene on and making their offspring a carrier. According to the National PKU Alliance, approximately 1 in every 50 people are carriers of the mutated gene that causes phenylketonuria, and phenylketonuria affects approximately 1 out of every 10,000 to 1 out of every 20,000 depending upon the country of origin. For some reason, this disorder also affects more Caucasians and Orientals than African Americans, but it doesn't appear to have more prevalence in either gender. The higher incidences of the disorder are found in the United States, Poland, and the Czech Republic. The National PKU Alliance also reports that there are approximately

14,500 people living in the United States with phenylketonuria. If a family has instances of phenylketonuria in their family, genetic counseling will probably be recommended. (National PKU Alliance) As mentioned earlier, phenylketonuria is not only a genetic disorder, but it is also a metabolic disorder. The children born with this disorder are unable to break down the amino acid phenylalanine due to the lack of the enzyme phenylalanine hydroxylase. When the phenylalanine builds up in the blood stream, it forms into phenyl pyruvate (phenylketones) which is toxic in excess. These phenylketones usually spill over into the urine which gives the disease its name. It eventually makes its way to the brain which causes a a lot of physical and mental side effects. The following are side effects listed by the Mayo Clinic for untreated phenylketonuria. 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 (“Phenylketonuria”, Mayo Clinic) These side effects are caused by the toxic effects that excess unmetabolized phenylalanine (phenyl pyvurate) built up in the blood stream can cause on the brain and nervous system. “The deffective enzyme in PKU, PAH, has the job of changing some oh the Phe you eat into tyrosine (Tyr). Tyr is used to make a brain neurotransmitter (messenger) chemical called dopamine. Evidence suggests that changes in PAH function in PKU can cause lower amounts of dopamine in the brain. Some symptoms of low dopamine include drastic mood swings difficulty in paying attention, and sleep disturbances.” Children with untreated, undiagnosed phenylketonuria usually suffer from severe irreversible mental retardation. Though this may seem like a sad fate, this disorder is very easily detected...
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