A NOVEL GERM-LINE P53 MUTATION IN INTRON-6 IN DIVERSE CHILDHOOD MALIGNANCIES

Screening for p53 mutations in exons 5 to 8 in 124 pediatric malignanc ies identified 18 abnormal shifts using single strand conformation pol ymorphism: 12 were missense mutations and in 6, no mutation was detect ed in the exon or in the splice donor acceptor sequences. Sequencing w as then performed in the adjacent introns, revealing a G to A base sub stitution at 39 base pairs upstream to exon 7. This mutation was ident ified in the germ line of five of the patients, and also in the father of one, whose parents mere available. For comparison, of the 184 norm al controls similarly screened, only one had this mutation (P=0.036). Positive staining of p53 protein was observed in three of the paraffin embedded tissues that were available: brain tumor, rhabdomyosarcoma, and lymphocytes from a normal lymph node from the rhabdomyosarcoma pat ient. All tumors with the identified intron mutation were Li-Fraumeni syndrome tumors. Sequencing of all exons including splice sites was pe rformed and revealed no mutation. We suggest that this mutation in int ron 6 of the p53 gene stabilizes the mild type p53 protein, resulting in its abnormal accumulation. Mutations in the noncoding region of p53 should be further studied.