screening for mutations in the phenylalanine hydroxylase gene from italian patients with phenylketonuria by using the chemical cleavage method a new splice mutation to investigate the molecular basis of phenylketonuria in italy we applied the chemical cleavage method ccm on amplified dna encompassing exons 7 and 8 of the phenylalanine hydroxylase gene these exons are in a region likely to be involved in enzyme function using this approach we could simultaneously screen for novel mutations and for seven reported mutations which map in this area three mutations were identified the first was shown to be a not previously described mutation a ga substitution at the 5 donor junction splice site of intron 7 the second change was a reported ga mutation at codon 261 the third change corresponded to a polymorphism at codon 245 our results indicate that ccm analysis of amplified genomic dna fragments can be successfully used to search for mutations in large genes whose transcripts are not readily available