PKU


 * Phenylketonuria, or PKU, is a very rare birth defect, and occurs when an enzyme, called “phenylalanine hydroxylase” (PAH), is either missing or not working properly. The job of this enzyme is to chemically change the amino acid phenylalanine into other substances. When a child with PKU eats food containing Phe, it builds up in the blood and causes problems. Phe is found in almost every food, except pure __fat__ and sugar.
 * It is an autosomal recessive disorder, which means it is not sex-linked and passed on by the recessive gene.
 * A parent could be heterozygous and not have the gene, which would make them a carrier.
 * Babies with the disease are required to be on a very strict, low phenylalanine diet, or risk mental retardation or microcephaly (an abnormally small sized head).
 * PKU can usually be detected by a blood test, and in most states that blood test is required for all newborns. If the screening test is positive then further analysis is required to confirm the diagnosis.
 * PKU was identified in 1984, and was found to be located on chromosome 12.

This diagram shows how phenylketonuria is an autosomal recessive disorder.