Phenylketonuria

=Phenylketonuria (PKU) //By Kellie Jackson and Sarah Martin//=

__Genetic Background and Significance: __
Affecting approximately one out of 12,000 infants, phenylketonuria, or PKU, is a genetic disease caused by enzyme abnormalities. Having been first discovered among the genetic information of two mentally retarded people, PKU is linked to mental retardation and a lack of the protein tyrosine; the abnormal enzyme phenylalanine hydroxylase, responsible for the conversion of phenylalanine to tyrosine, is not active in those affected by PKU. As a result, great and superfluous levels of phenylalaine are present in the body. Furthermore, the significance of this disease lies in the fact that it is classified as being caused by autosomal recessive mutant alleles and is passed from the parents of the offspring. More specifically, the disease is caused by a mutation in the PAH gene, located on chromosome 12. Even though the location of the mutation is known, the specific type of mutation varies. This variation changes the intensity of the clinical course of the disorder. Missense mutations occur on the PAH gene 62% of PKU cases; a missense mutation is a point mutation in which a single nucleotide is changed, resulting in a codon that codes for a different amino acid . Deletions, splicing defects, silent polymorphisms, nonsense mutations, and insertions are other types of mutations that could lead to PKU.

__Symptoms: __
The early diagnosis of PKU is essential because the symptoms are not obvious in an infant. Without diagnosis, mental retardation may develop gradually and probably won't be apparent for a few months. Growth of those affected may be significantly slower than a normal infant. Reoccurring seizures may also harm an infant with this disease. The presence of phenylacetic acid in urine and perspiration is also a symptom. However, an early, visual clue to the disease is the light coloring of skin and hair, eczema, and a musty odor. The disease causes light coloring of skin and hair because the production of tyrosine, an enzyme that produces pigment melanin responsible for darker colors, is inhibited by PKU.

__Important Extra Details __:
Detection of PKU in newborn infants is carried out through blood screenings after birth; however, it is not always accurate to assume the levels of phenylalanine in the babies' blood are congruent to the level of phenylalanine hydroxylase activity in the babies' livers. The blood screening test was designed by Robert Hutherie in the mid-twentieth century and requires the blood to be added to phenylalanine-dependent auxotrophic bacteria- samples with great bacterial growth can be concluded to also contain high levels of phenylalanine.

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Treatment of PKU is relatively simple after early detection. The disease may be treated with a change in diet, aimed towards lowering levels of phenylalanine in consumed food. It is important to treat PKU as early as possible to avoid any brain damage.=====

__Differences Between a Normal Infant and an Infant with PKU: __
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__Video Explanation: __
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