GENETIC AND FUNCTIONAL-STUDIES OF A GERMLINE TP53 SPLICING MUTATION IN A LI-FRAUMENI-LIKE FAMILY

We report an extensive Li-Fraumeni-like family in which there is an un usual spectrum of tumours at relatively late onset. A germline TP53 sp lice donor mutation in exon 4 is present in all affected family member s available for testing. The mutation abolishes correct splicing of in tron 4 and techniques of RT-PCR have identified three different aberra nt transcripts from the mutant TP53 allele. Using the yeast functional assay to analyse transcripts in cells from a number of family members with the mutant allele, TP53 appears wild-type, Functional studies ha ve been carried out on cells from patients with and without cancer who carry the germline mutation, and on cells from unaffected individuals from the same family who do not carry the mutation. Using a number of functional endpoints known to distinguish between cells carrying muta nt or wild-type TP53 alleles, we were unable to discriminate normal (w t/wt) from heterozygous (wt/mut) cells by lymphocyte apoptosis and fib roblast survival following low dose rate ionising radiation exposure. However germline mutation carriers show increased sensitivity to radia tion-induced chromosome damage in the G(2) phase of the cell cycle, an d decreased transient and permanent G(1) arrest. These studies demonst rate the importance of fully characterising the effects of TP53 germli ne mutations, and may explain some of the phenotypic features of this family.