PKU+(Phenylketonuria)

__Phenylketonuria(PKU)__
Phenylketonuria (PKU) is a human genetic disease affecting 1 in 10,000 newborns in the United States. A relationship between genetics and the environment can have an extreme impact on an individual. The disease is characterized by a mutation in the gene coding for the enzyme phenylalanine hydroxylase (PAH). The enzyme is used to metabolize phenylalanine into tyrosine by adding a hydroxyl group onto the benzene ring of phenylalanine. PAH is regulated by phosphorylation, and substrates phenylalanine and(6R)-l-erythro-5,6,7,8- tetrahydrobiopterin (BH 4 ) (Kobe et al., 1999). In individuals with this disorder, the gene encoding for this enzyme is mutated, creating a nonfunctional enzyme that is unable to convert the amino acid. Going undiagnosed, the individual develops negative traits including mental impairment, foul smelling urine, and possibly mental retardation (Brooker, 2009). Untreated newborns appear normal at birth but fail to reach developmental milestones. The childs normal appearence at birth is attributed to maternal effect. While the fetus is in the uterus, the mother's PAH gene transcribes and translates enough phenylalaine hydoxylase to convert phenylalanine to tyrosine for the fetus. Once the child is born, the mother's enzymes are no longer available and phenylpyruvic acid begins to build, resulting on the onset of PKU symptoms (McComas, unknown). Symptoms of the disease begin to appear at 3-4 months. Neuro-physiological distress, such as deficient muscle tone or spastic paraplegia, are the first symptoms to appear. Around the age of 1 impaired muscle movements such as exaggerated tendon reflexes and involuntary movements develop in the child (Anton, Tocan, Iliescu, Diaconu, 2011).

__Discovery__
Borgney and Harry Egeland married and had two children. Their daughter reached age 3 and still had not begun to talk. Her younger brother was much further behind his sister in development when at 16 months he had not sat up by himself. During their infancy, the parents noticed the children's urine had a strange odor and wondered if this could possibly be the reason for their children's slow development. Harry Egeland had taken a class in dental school under Dr. Asbjorn Folling, so after he tried to see several doctors, Egeland went to see his professor. Several urine tests were done and all came back normal except for one. When Folling added a few drops of iron salt to the children's urine, the color changed to a dark green color which faded after a few minutes. During normal urine tests, the urine would turn a red-brown color. Following this discovery, Dr. Folling performed test after test to discover what would make the children's urine turn green. The green color is associated with phenylpyruvic acid, which causes the musty odor. There were 430 other mentally disabled children tested, eight of the children's urine tests came back positive for phenylpyruvic acid (Centerwall & Centerwall, 2000).

__Genes Involved__
Phenylketonuria is caused by mutations in the PAH gene located on chromosome 12 at the location 12q22. Thirty-five separate mutations have been identified as causes for PKU, including 21 missense, 8 splice site, 3 nonsense, 2 single nucleotide deletions, and 1 in-frame deletion (Karacic, 2009). Four separate mutations have been identified as main causes of PKU. These four account for 90% of all cases of PKU, but over 70 other mutations have been identified as having an effect on PAH properties. The most common mutation, known as IVS12DS, G-A, +1, accounts for nearly 38% of PKU cases. It occurs at the splice site for the number 12 exon. It causes a premature stop codon which results in a shortened RNA strand, resulting in a non-functioning protein. Patients that are afflicted with this mutation exhibit typical PKU symptoms. The second mutation is responsible for 20% of PKU and is known as Arg408 to Trp. It is a simple base substitution in the DNA that results in Argenine being replaced with Tryptophan. Although only a single base change, it is very significant and causes classic PKU symtoms due to a non-functional PAH protein. The final two mutation are very similar. These mutations are characterized by the replacement of argenine with a glutamine. These mutations do not fully inhibit the PAH enzyme. Mutantions allow that enzyme to function, but at a much lower level of function than in a healthy individual (Roberts). The other 10% of mutations are caused by over 70 separate mutations (Dobrowolski, 2011, Karacic, 2009, Roberts, N.D.).The PAH gene contains 13 exons making up the actual gene encoding for the PAH enzyme. A mutation in any of these exons may alter the sequence enough to produce a nonfunctional PAH enzyme (Williams, Mamotte, & Burnett, 2008).

__Inheritance__
PKU is an autosomal recessive inherited disease. A mutation on chromosome 12 displays an incorrect sequence to code for PAH as stated previously. This trait will then follow normal mendelian inheritance. If both parents are carriers of the disease, one out of four children should display PKU symptoms as shown in the figure below. Every individual has two copies of an allele for any particular gene. Only when both recessive alleles are inherited and mutated, coding for a nonfunctional PAH enzyme, will the individual display symptoms of PKU. When an individual has one allele coding for a nonfunctional PAH enzyme, but the other allele codes for a normal PAH enzyme, the individual will not display symptoms of PKU (Brooker, 2009).

__Possible Treatments__
There is currently no medical cure for PKU. Precautionary measures are taken at the birth to prevent the onset of the disease. Newborns are tested a few days after birth. An infant's outer heel is pricked on the face side of the plantation areas. This area is then heated for 3-5 minutes and then cleaned with alcohol and air dried. The blood is then taken on a special filter paper. The blood must be carefully taken, avoiding any added pressure to the area as to avoid hemolysis or contamination by other tissue fluids. The test strip is then air dried and sent to a lab (Anton, Tocan, Iliescu, & Diaconu, 2011).

Early diagnosis of the disease allows for prevention of any negative attributes associated with the disease. The environment has an extreme affect on the outcome of the disease. Dietary guidelines can help in the prevention of development of PKU traits. Food containing high levels of protein cause a build up of phenylpyruvic acid. Diets avoiding protein rich foods prevent the development of PKU traits. Meats, legumes, nuts, dairy products and some medications must be avoided. (See link for list of medications containing phenylalanine: [] (Schuett, 2011) )

An additional treatment that is not always have an effect is the use of BH 4. Some patients are able to see reduced levels of phenylalanine in the blood when BH 4 is administered into the patient. The effectiveness of the cofactor may be related to mutations in PAH at the active site where BH 4 normally binds PAH. The increased concentration of BH 4 may allow more enzyme activity by PAH because there is more of this particular cofactor to increase the likelhood of BH 4 to bind to PAH (Leuzzi et al., 2006). The effectiveness of this type of treatment is based on where the mutation originally took place. If the active site for the cofactor was not affected with the original mutation, this treatment will likely not be beneficial to that patient. It is also not entirely effective with patients that did have a mutation at the active site. It is not a very successful treatment, but it helps which may allow the patient to eat a little bit of foods they don't normally get to. It is also a start to finding newer, more effective types of treatment.

__References__
Anton, D. T., Tocan, L., Iliescu, L., & Diaconu, G. (2011). New born screening for phenylketonuria-a chance at life. //Romanian Journal of Pediatrics//, //60//(22), Retrieved from http://ehis.ebscohost.com/eds/pdfviewer/pdfviewer?sid=063ea5d7-1c7d-4ded-b31a-bb73b283e624@sessionmgr113&vid=10&hid=101

Brooker, R. J. (2009). //Genetics: Analysis & principles//. (3 ed., pp. 76,602). New York: McGraw-Hill

Centerwall, S. A., & Centerwall, W. R. (2000). //The discovery of phenylketonuria: the story of a young couple, two retarded chilren and a scientist//. (pp. 89-103). Retrieved from []

D., N. (2009, November 24). [Web log message]. Retrieved from [] McComas. (unknown). //Genetic disorders//. Retrieved from []

 Dobrowolski, Steven. (2011). "Molecular genetics and impact of residual in vitro phenylalanine hydroxylase activity on tetrahydrobiopterin responsiveness in Turkish PKU population." // Molecular Genetics and Metabolism //. 102.2: 116-21. Print.

 Karacic, Iva. "Genotype-predicted tetrahydrobiopterin (BH4)-responsiveness and molecular genetics in Croatian patients with phenylalanine hydroxylase (PAH) deficiency." // Molecular Genetics and Metabolism //. 97.3 (2009): 165-71. Print.

Kobe, B., Jennings, I.G. , House, C.M. , Michell, B.J. , Goodwill, K.E. , Santarsiero,. . .Kemp, B.E. (1999). Structural basis of autoregulation of phenylalanine hydroxylase. //Nature Structure Biology.// 6(5),442-448.

Leuzzi, V., Carducci, C., Carducci, C., Chiarottie, F., Artiola, C., Giovanniello, T., & Antonozzi, I. (2006). The spectrum of phenylalanine variations under tetrahydrobiopterin load in subjects affected by phenylalanine hydroxylase deficiency. //Journal of Inherited Metabolic Disease.// 29, 38-46.

Roberts, Will. "Phenylketonuria-The Genetic Mutations and Mode of Inheritance." . N.p., n.d. Web. 1 Apr 2012. [].

Schuett, V. (2011, September). //National pku news//. Retrieved from http://www.pkunews.org/

 Williams, R. A., Mamotte, C.D., & Burnett, J.R. (2008). Phenylketonuria: an inborn error of phenylalanine metabolism. // The Clinical Biochemist, // 29(1), 31-41.