substitutions such as missense, nonsense, and splicing mutations. This mutation causes a near or complete deficiency of the enzyme phenylalanine hydroxylase, which converts phenylalanine into another amino acid, tyrosine. As a result, PHE accumulates in the blood and in other parts of the body, which prevents the brain from developing normally. A normal blood phenylalanine level is about 1 mg/dl. With PKU, levels range from 6 to 80 mg/dl but are usually greater than 30 mg/dl.Phenylketonuria is a single gene disorder, meaning that, a mutant or abnormal gene causes the disorder. PKU is inherited in an autosomal recessive fashion. This means that the affected individual must have two defective genes in order to have the disorder. People with only one copy of the defective gene are called carriers and show no symptoms of having the disease. In order for a child to inherit PKU, both parents must be carriers. When this occurs, there is a twenty-five percent chance of their producing an affected child and a twenty-five percent chance that both of the normal genes will be passed on. There is also a fifty-percent chance that a baby will inherit the PKU gene from one parent and the normal gene from the other, making the baby a carrier like his or her parents. These chances remain the same for each pregnancy and males and females are equally likely to inherit this disease. Other characteristics of an autosomal recessive genetic disorder that apply to PKU include clustering of the disease phenotype among siblings and consanguineous mating accounts for five percent of the cases of PKU. The prevalence of Phenylketonuria in the United States is approximately 1 in 10,000 to 15,000 births, which is most commonly present in Caucasians. Approximately 1 person in 50 has inherited a PKU allele. This means that some 5 million people in the United States are carriers. Internationally, the disease frequency varies by population. Turkey has the...
