A number of techniques have been used to identify mutations in APC including SSCP, DGGE, heteroduplex analysis, RNase protection and chemical mismatch cleavage. Each technique has advantages and disadvantages including sensitivity, price and safety and the choice of which method to use will depend on the individual circumstances in each laboratory. In each of these techniques exons 1-14 and approximately 23 overlapping segments of exon 15 are analysed separately. Exons 1-14 can be analysed in a single step but this requires RNA as starting material. PTT of exon 15 works extremely well although there are more problems with exons 1-14.
Clinical information can be of help when deciding to look for mutations.
An attenuated phenotype is associated with mutations in exon 3. Desmoid tumours are associated primarily with mutations after codon 1444. Cytogenetic Analysis De novo and inherited deletions detectable cytogenetically have been identified in a number of families. Chromosome investigations are worth carrying out if no mutations have been found using the techniques listed above. In the majority of families, presymptomatic diagnosis at the molecular level should only be carried out once the children are due to start regular bowel examination.