BRCA1 mutations and phenotype

The BRCA1 3'-UTR: 5711+421T/T_5711+1286T/T genotype is a possible breast and ovarian cancer risk factor

BACKGROUND

A significant proportion of familial and early-onset breast and ovarian cancers occur in individuals without coding mutations of BRCA1 and BRCA2.

AIMS

We identified genetic variation at 3'-untranslated region (UTR) of BRCA1 in familial and early-onset breast and ovarian cancer patients both with and without BRCA1/2 mutation in the coding regions (BRCA1/2 pos and BRCA1/2 neg), and verified the possible cancer risk factor of the specific 3'-UTR variation using functional analysis.

METHODS

BRCA1 SNP analysis was screened in 46 patients and 103 unaffected Thais by heteroduplex analysis and DNA sequencing. After chi-square test for the potential cancer association of the specific 3'-UTR genotypes, the functional tests were conducted using several strategies of the luciferase gene expression model.

RESULTS

We document the existence of two 3'-UTR polymorphic sites, the 5711+421(G or T) and the 5711+1286(C or T). Frequency of homozygous genotype 5711+421T/T_5711+1286T/T (or T/T-T/T) in the group of BRCA1/2 neg cancer patients was triple of that seen in unaffected persons and showed a significant cancer association (p = 0.007). Functional analysis of these polymorphic sites using luciferase experiments showed an obvious significant reduction in activity associated with the T allele at both sites.

CONCLUSION

These results suggest that the inheritance of specific 3'-UTR polymorphisms may predispose individuals to early-onset or familial breast or ovarian cancer.

Inherited predisposition and breast cancer: modifiers of BRCA1/2-associated breast cancer risk

Germline mutations in the BRCA1 and BRCA2 (BRCA1/2) genes explain a substantial proportion of hereditary breast and ovarian cancer. Women who have inherited a mutation in one of these genes are at increased risk to develop breast and/or ovarian cancer, although there is variability in the manifestation of tumors by age and site. This variability may be explained, in part, by the BRCA1/2 mutation type or location. However, it is also possible that risk-modifying factors exist that explain interindividual variability in cancer risk. These factors include genes at other loci and endogenous or exogenous exposures. A more complete understanding of factors that modify cancer risk in BRCA1 and BRCA2 mutation carriers may help to refine estimates of cancer risk. A number of exposures, including reproductive history and exogenous hormone use, have been implicated as BRCA1/2-associated cancer risk modifiers. Similarly, genes involved in hormone metabolism, including the AIB1 and AR genes, have been linked with altered breast cancer risk. Therefore, although germline BRCA1/2 mutations raise a woman's breast and ovarian cancer risk, other factors may interact with BRCA1/2 mutations to modulate this risk.

A targeted mouse Brca1 mutation removing the last BRCT repeat results in apoptosis and embryonic lethality at the headfold stage

A mouse model with a targeted mutation in the 3' end of the endogenous Brca1 gene, Brca1(1700T), was generated to compare the phenotypic consequences of truncated Brca1 proteins with other mutant Brca1 models reported in the literature to date. Mice heterozygous for the Brca1(1700T) mutation do not show any predisposition to tumorigenesis. Treatment of these mice with ionizing radiation or breeding with Apc, Msh-2 or Tp53 mutant mouse models did not show any change in the tumor phenotype. Like other Brca1 mouse models, the Brca1(1700T) mutation is embryonic lethal in homozygous state. However, homozygous Brca1(1700T) embryos reach the headfold stage but are delayed in their development and fail to turn. Thus, in contrast to Brca1(null) models, the mutant embryos do not undergo growth arrest leading to a developmental block at 6.5 dpc, but continue to proliferate and differentiate until 9.5 dpc. Homozygous embryos die between 9.5-10.5 dpc due to massive apoptosis throughout the embryo. These results indicate that a C-terminal truncating Brca1 mutation removing the last BRCT repeat has a different effect on normal cell function than does the complete absence of Brca1.

Genetic counseling impacts decision for prophylactic surgery for patients perceived to be at high risk for breast cancer

BACKGROUND

This study addresses the impact a comprehensive genetic counseling program had on women considering prophylactic mastectomy or oophorectomy.

METHODS

Sixty patients underwent detailed family evaluation and risk was estimated. Recommendations were made regarding testing. Ramifications of testing were discussed in detail.

RESULTS

Thirty-one women (37%) were considering prophylactic surgery believing themselves to be at high risk. Of these, 23 had testing recommended. Seven patients proceeded with prophylactic surgery based solely on high-risk assessment. Ten women were tested; five were positive. Three patients proceeded with prophylactic surgery despite a negative test. One decided against surgery despite a positive test. After counseling, prophylactic surgery was performed in just over half the initial candidates.

CONCLUSIONS

Breast cancer risk estimation and genetic evaluation can be complex. Comprehensive genetic risk assessment programs can play a significant role in the management of patients considering prophylactic surgery for perceived high risk.

Inherited genetic predisposition in breast cancer. A population-based perspective

Two classes of inherited susceptibility genes may be considered in the etiology of breast and other common cancers. First, genes have been identified that confer a high degree of breast cancer (BC) risk, usually associated with hereditary syndromes, but disease-associated germline variants in these genes are relatively rare in the general population. These include BRCA1, BRCA2, and TP53. The proportion of BC in the general population that can be explained by these genes is relatively small. Second, variant genotypes at other loci may confer a relatively smaller degree of cancer risk, but they are carried by a larger proportion of the general population. As a result, the proportion of BC that could be explained by these genes may be relatively large. To understand the genetic basis for BCs in the general population, both of these classes of genes may need to be considered. This paper presents an overview of genes thought to be involved in BC susceptibility. Genes that confer a high degree of risk are more likely to result in hereditary patterns of cancer that are amenable to identification by genetic epidemiologic methods using pedigree data. More common (e.g., nonhereditary) forms of BC may be optimally analyzed by molecular epidemiologic studies using case-case, case-control, or cohort designs. The use of an appropriate study design is crucial to the identification of genes with relatively small effects on BC risk. To understand the inherited factors that explain BC in the general population, consideration should be given to genes with different allele frequencies and magnitudes of effect, using appropriate analytical approaches. By understanding the complex interactions of these genes with one another and with exposures, improved risk assessment and potential for targeted cancer prevention strategies may be possible.

BRCA1 and BRCA2 proteins: roles in health and disease

Between 5% and 10% of all breast cancer is hereditary, with patients having a strong family history of the disease. The remaining 90-95% of cases are classed as sporadic. Within the inherited group, 80-90% of cases are the result of germline mutations affecting two recently identified genes: BRCA1 and BRCA2. Since the sequencing of these genes, considerable research on the genetics of the mutation carriers has been performed, with less attention having been focused on the BRCA1 and BRCA2 proteins themselves. The structure and function of the protein products thus continues to hold mystery and might be the key to the full understanding of this complex disease.