accumulation of excess phenylalanine causes _________________.
Classical PKU is caused by a deficiency of the enzyme phenylalanine hydroxylase (PAH). Over 70 different mutations on the PAH gene found on Chromosome 12 have been found to cause the almost complete absence of PAH as seen in PKU patients. PKU patients deficient in PAH are unable to metabolise the amino acid phenylalanine leading to an accumulation of phenylalanine and it's metabolites within the body. PKU is an example of an autosomal recessive disorder.