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.