Low rate of TP53 germline mutations in breast cancer/sarcoma families not fulfilling classical criteria for Li-Fraumeni syndrome.
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Adult↗
Biomedical subjects
G McGown
Publications and source records attributed to G McGown.
Characterization of germline TP53 splicing mutations and their genetic and functional analysis.
Germline TP53 splicing mutations have been described infrequently (>2%) in the literature, however in a series of 40 patients and families identified by our group in which there are germline TP53 mutations, seven affect splicing (18%). The low figure reported in the literature might reflect the method of mutation detection, which in many studies does not include all splice junctions. These data indicate that a significant proportion of TP53 germline mutations are currently unrecognized. We have carried out detailed studies of the effects of the different mutations on splicing, and see distinct variations in the effects of the same mutation in different patients. Furthermore we have identified the usage of a non-consensus splice donor site in four families with an intron 4 splice donor mutation.
Alternative Splicing↗
Significance of intron 6 sequence variations in the TP53 gene in Li-Fraumeni syndrome.
Many polymorphisms have been reported in the TP53 gene. Some of these are within the coding region, and may affect the function of the p53 protein, others are within introns or non-coding regions, and their significance is unclear. Recently, a number of publications have claimed that polymorphisms within intron 6 are responsible for inherited predisposition to childhood malignancies, familial breast cancer, and Li-Fraumeni syndrome (LFS). We find no evidence for intron 6 sequence variants predisposing to LFS in our cohort of families and, furthermore, we show that some of the conclusions of other groups cannot be supported by data from our analysis.
Genes, p53↗
Exclusion of the genes CDKN2 and PTEN as causative gene defects in Li-Fraumeni syndrome.
We have analysed Li-Fraumeni syndrome families, previously shown to be negative for mutations in TP53, for mutations to the tumour suppressor genes PTEN and CDKN2. These genes function in cell cycle progression or are mutated in a variety of tumours. We have detected no mutations in the family members tested.
DNA Mutational Analysis↗
Are there low-penetrance TP53 Alleles? evidence from childhood adrenocortical tumors.
We have analyzed a panel of 14 cases of childhood adrenocortical tumors unselected for family history and have identified germline TP53 mutations in >80%, making this the highest known incidence of a germline mutation in a tumor-suppressor gene in any cancer. The spectrum of germline TP53 mutations detected is remarkably limited. Analysis of tumor tissue for loss of constitutional heterozygosity, with respect to the germline mutant allele and the occurrence of other somatic TP53 mutations, indicates complex sequences of genetic events in a number of tumors. None of the families had cancer histories that conformed to the criteria for Li-Fraumeni syndrome, but, in some families, we were able to demonstrate that the mutation had been inherited. In these families there were gene carriers unaffected in their 40s and 50s, and there were others with relatively late-onset cancers. These data provide evidence that certain TP53 alleles confer relatively low penetrance for predisposition to the development of cancer, and they imply that deleterious TP53 mutations may be more frequent in the population than has been estimated previously. Our findings have considerable implications for the clinical management of children with andrenocortical tumors and their parents, in terms of both genetic testing and the early detection and treatment of tumors.
Adaptor Proteins, Signal Transducing↗
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 unusual spectrum of tumours at relatively late onset. A germline TP53 splice donor mutation in exon 4 is present in all affected family members available for testing. The mutation abolishes correct splicing of intron 4 and techniques of RT-PCR have identified three different aberrant 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 have 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 mutant or wild-type TP53 alleles, we were unable to discriminate normal (wt/wt) from heterozygous (wt/mut) cells by lymphocyte apoptosis and fibroblast survival following low dose rate ionising radiation exposure. However germline mutation carriers show increased sensitivity to radiation-induced chromosome damage in the G2 phase of the cell cycle, and decreased transient and permanent G1 arrest. These studies demonstrate the importance of fully characterising the effects of TP53 germline mutations, and may explain some of the phenotypic features of this family.
Adult↗
A novel TP53 splicing mutation in a Li-Fraumeni syndrome family: a patient with Wilms' tumour is not a mutation carrier.
We report a Li-Fraumeni syndrome family in which we have detected a splice acceptor mutation in intron 3 of TP53. The mutation affects one of the invariant residues at the splice acceptor site, as a result of which two aberrant transcripts are produced. A child with Wilms' tumour aged 3 years in this family was shown not to be a mutation carrier.
Child, Preschool↗
Germ-line mutations of TP53 in Li-Fraumeni families: an extended study of 39 families.
We have previously reported on the analysis of TP53 coding mutations in 12 classic Li-Fraumeni syndrome (LFS) families plus 9 families that were Li-Fraumeni-like (LFL) families (J. M. Birch et al., Cancer Res., 54: 1298-1304, 1994). Mutations were found in 6 of 12 LFS families and in 1 of 9 LFL families. We have now extended these studies to include an additional nine LFS and nine LFL families, and TP53 mutations have been detected in eight of nine LFS families and in three of nine LFL families. Six of the new mutations described here are the same as those previously identified in other Li-Fraumeni families and are missense mutations at codons 245, 248, and 273 (in two families); a nonsense mutation at codon 209; and a mutation at the splice donor site in exon 4. The other five mutations are novel germ-line mutations and include missense mutations at codons 136 and 344, a 2-bp deletion within codon 191, a splice acceptor mutation in intron 3, and a 167-bp deletion of part of exon 1 and intron 1. In addition, we have detected a codon 175 mutation in a family previously reported as TP53 negative. To summarize all of the data from the families we have studied in this and our previous report (J. M. Birch et al., Cancer Res., 54: 1298-1304, 1994), mutations have been detected in 15 of 21 LFS families (71%) and in 4 of 18 LFL families (22%). These figures are somewhat higher than those previously reported by us and others for the frequency of TP53 mutations in LFS and LFL families. This could reflect our analysis of all 11 exons of TP53, including noncoding regions, as well as the use of direct sequencing rather than other less-sensitive mutation detection methods.
Female↗
A detailed study of loss of heterozygosity on chromosome 17 in tumours from Li-Fraumeni patients carrying a mutation to the TP53 gene.
We have studied a total of 36 tumours from 28 patients with germline mutations to the TP53 gene for loss of heterozygosity at TP53 using techniques of both direct sequencing and restriction fragment length polymorphism analysis. All patients were from families conforming to the definition of classical Li-Fraumeni syndrome (LFS) or were Li-Fraumeni-like (LFL). The data we have obtained show that loss of the wild-type TP53 gene is observed in under half (44%) of all tumours, and that the pattern of LOH at TP53 may be mutation specific. LOH has been observed in premalignant as well as invasive tumours. Two tumours (6%) show loss of the mutant allele and retention of the wild-type. To confirm that TP53 is indeed the target for LOH events on chromosome 17, we have used additional microsatellite repeats to examine patterns of allelic imbalance along the length of chromosome 17. Data from this analysis indicate that TP53 is the target of loss, but reveal some other interesting patterns of allelic imbalance at other loci on chromosome 17.
Chromosome Deletion↗
A previously undescribed mutation within the tetramerisation domain of TP53 in a family with Li-Fraumeni syndrome.
We report details of a family with classic Li-Fraumeni syndrome in which there is a mutation in codon 344 of the tumour suppressor gene TP53. Codon 344 is a key residue within the tetramerisation domain, and the amino acid substitution of a proline for a leucine is predicted to have profound implications for tetramerisation and potentially DNA binding. This is the first report of a mutation at this residue in either sporadic tumours or in the germline and the first report of a germline mutation within the tetramerisation domain. The family does not appear to be remarkable in the spectrum of tumours, and there is loss of the wild-type allele in a leiomyosarcoma from the proband. A cell line has been established from the tumour of the proband and cytogenetic and molecular studies carried out, providing an extensive analysis in this family.
Adult↗
A novel deletion within exon 6 of TP53 in a family with Li-Fraumeni-like syndrome, and LOH in a benign lesion from a mutation carrier.
We report here a family with some of the characteristics of Li-Fraumeni syndrome (Li-Fraumeni-like) in which there is a 2 base pair deletion within exon 6 of TP53 in two affected individuals. Of particular interest in this family is a study of loss of heterozygosity (LOH) of the TP53 gene, and the finding that there is LOH in all cancers available for study from mutation carriers, and additionally from a benign endometrial polyp from one of those patients. Two other family members, one with a rectal carcinoma aged 55, the other with two separate benign lesions under the age of 45, were both wild-type for the TP53 mutation.
Adult↗
Allelic imbalance of chromosome 6q in ovarian tumours.
Previous work has implicated putative tumour-suppressor (ts) genes at 6q27 and a broad region at 6p12-q23. Here we report the results of a coded, randomised study of allelic imbalance at 12 loci on 6q on 40 pairs of coded tumour-blood pairs from patients with ovarian tumours. Our results provide clear evidence for the involvement of different regions of 6q in tumours of different histological subtypes. The involvement in serous tumours of a ts gene at the distal site is confirmed. However, proximal 6q presents a complex picture, with possibly three further ts genes: one at 6q21-23.3 involved at high frequency in benign and endometrioid tumours, another at 6q14-q15, also involved in endometrioid tumours, and a third suggested by a smallest region of deletion at 6q16.3-q21, between D6S275 and D6S300, that appears to be involved in early stage tumours. These observations point the way to a statistical study of the involvement of 6q in tumours of different histological type and staging performed on larger cohorts of samples.
Adenocarcinoma, Mucinous↗
Proximal 6q, a region showing allele loss in primary breast cancer.
To define regions of deletion of chromosome 6q in breast cancer, we scored 18 (CA)n microsatellites for allelic imbalance (AI) in 42 paired blood/tumour samples. Heterozygosity frequencies of the markers in the sample population ranged from 31% to 92% (mean 68%). Two regions of the chromosome arm showed AI values greater than the background range of 10-22% (mean 17%) of informative cases that was observed with five markers spanning 6q21-q25.2. Firstly, seven markers gave AI values that averaged 35% in a region flanked by D6S313 (AI = 10%) at 6q13 and D6S283 (AI = 17%) at 6q16.3-21. The second region showed marginally increased AI at 6q25.2-q27 and included D6S193, previously shown to be close to a tumour-suppressor gene involved in ovarian carcinoma. Since AI of 6q in breast cancer was shown previously to be due predominantly to loss of heterozygosity, our results suggest the presence of at least two tumour-suppressor genes on 6q that are involved in breast cancer. The proximal region has not been recognised in breast cancer before and is involved in a higher frequency of tumours than the distal region.
Alleles↗
An extended Li-Fraumeni kindred with gastric carcinoma and a codon 175 mutation in TP53.
We present an extended family with Li-Fraumeni syndrome characterised by gastric and breast carcinoma, glioma, sarcoma, and leukaemia. This family showed strong evidence of linkage to TP53, and three of four tumours analysed showed loss of the wild type allele. A codon 175 missense mutation was identified in exon 5 in all available affected subjects. Counselling, screening, and issues surrounding presymptomatic testing are discussed.
Codon↗
Physical mapping of 43 STSs to human chromosome 6.
We have localized 43 sequence-tagged sites by deletion mapping using a chromosome 6 panel of 18 translocation hybrids. Thirty-four loci were mapped to the long arm of chromosome 6, and 9 were mapped to 6p. Many of the loci contain (CA)n dinucleotide repeated sequences and therefore will be useful markers for mapping genes on chromosome 6.
Alleles↗
Thirteen dinucleotide repeat polymorphisms on chromosome 6.
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Base Sequence↗