Phenylketonuria
Allany and Madeline
PKUbiosci.jpg


Nature of the Genetic Difficulty

PKU is caused by a mutation of the phenylalanine hydroxylase (PAH) gene on the 12th chromosome. So far, over 500 mutations of this gene have been known to cause PKU. Most of them tend to change a single nucleotide in the sequence that codes for phenylalanine hydroxylase. The most common mutation replaces the amino acid "arginine" with the amino acid "tryptophan" at position 408.

Basis Facts of Disease

Symptoms • Delayed mental and social skills • Head size significantly below normal • Hyperactivity • Jerking movements of the arms or legs • Mental retardation • Seizures • Skin rashes • Tremors • Unusual positioning of hands
Other significant visual indications would be lighter hair color, skin and eyes. This is due to the fact that Phenylalanine is important in the synthesis of melanin. In new born babies, the first symptoms can be seen in a few days to several weeks after birth. Elevated levels of phenylalanine result in a musty or mouse like odor to the urine. If untreated, the child will suffer from intellectual disabilities, behavioral problems, heart defects, skin disorders, and other related diseases
In the United States, PKU occurs in 1 in 10,000 to 15,000 newborns.

Prognosis

PKUtest.jpg
For reference, phenylalanine is often referred to by its amino acid abbreviation, PHE.
If the diet is closely followed, those suffering from PKU can be expected to lead a full life without further complications. If the disease is not detected early enough or the diet is not maintained, brain damage will result from the high buildup of phenylalanine in the blood. If left untreated, this can lead to mental retardation by the end of a child’s first year of life. Even with treatment, school function later in life may be mildly impaired. ADHD is a common problem seen in those who do not follow a low-protein/low-PHE diet. Another symptom that can arise from ignoring the diet later in life is stomach upset.
Luckily, PKU is a relatively simple disease to treat. It is entirely based on diet. Following a low-phenylalanine diet is of utmost importance in a child’s developmental years, as excess levels of PHE in the blood can have a detrimental effect on the brain’s growth. While it is only vital to follow the diet during these years, as the levels have a less harmful effect on the body as structures become more fully developed, those who remain on the diet throughout their lives tend to have “better physical and mental health”. If a person with PKU plans to have children in the future, it is incredibly important for the mother to follow a strict diet both before conception and throughout the pregnancy. High levels of PHE can negatively affect the growth of the fetus, even if it has not inherited the disease. As infants, babies with PKU cannot consume breast milk. They are required to have a special formula called Lofenalac, which, while low in phenylalanine, is rich in all other essential amino acids. (From personal experience, I can tell you that this formula both smells and tastes horrible. While it can be used as a protein source throughout life, it is not the most pleasant alternative. This is why many older PKU patients turn to supplements such as fish oil to replace the long chain fatty acids missing from their low-PHE diet.)

Sources Cited

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002150/ http://www.brighthub.com/science/genetics/articles/36096.aspx
http://ghr.nlm.nih.gov/gene/PAH
Personal Experience - Madeline's sister
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