Japanese Breast Cancer Families Research Articles

Functional analysis of BRCA1 missense variants of uncertain significance in Japanese breast cancer families

Germline mutations in the tumor suppressor genes BRCA1 and BRCA2 are responsible for a large proportion of familial breast cancer cases, and therefore, BRCA1 and BRCA2 genetic testing has become increasingly common in clinical practice. However, variants of uncertain significance (VUS) have been detected in 16.3% of Japanese patients suspected of having hereditary breast and ovarian cancers. The clinical importance of VUS is unknown, and their incidence has led to issues in risk counseling, assessment and treatment of cancer patients. In the present study, we performed functional analyses of two VUS in BRCA1, A1752G and Y1853C that were detected in two independent breast cancer patients who were suspected of having hereditary breast cancer. Segregation analysis revealed that Y1853C, but not A1752G, was cosegregated in affected family members. Conservation, transcription and structure analyses also supported the pathogenic potential of Y1853C. Detailed segregation and in silico and in vitro analyses will enhance our understanding of VUS and improve the management of cancer patients and their families.

Identification and evaluation of 55 genetic variations in the BRCA1 and the BRCA2 genes of patients from 50 Japanese breast cancer families.

We sequenced approximately 23 kb genomic regions containing all the coding exons and their franking introns of two breast cancer susceptibility genes, BRCA1 and BRCA2, of 55 individuals from 50 unrelated Japanese breast cancer families. We identified 55 single-nucleotide polymorphisms (SNPs) (21 in BRCA1 and 34 in BRCA2) containing nine pathogenic protein-truncating mutations (four in BRCA1 and five in BRCA2 from ten patients). Among the remaining 46 SNPs, allele frequencies of 40 were examined in both the breast cancer patients and 28 healthy volunteers with no breast cancer family history by PCR-RFLP or by direct DNA sequencing. Twenty-eight SNPs were common and were also found in the healthy volunteers and/or a SNP database. The remaining 18 were rare (allele frequency <0.05) and were not found in the healthy volunteers and/or the database. The pathogenic significance of these coding SNPs (cSNPs) remains to be clarified. The SNP information from this study will be useful in the future genetic testing of both BRCA1 and BRCA2 genes in the Japanese population.

Frequency ofBRCA1andBRCA2Germline Mutations Detected by Protein Truncation Test and Cumulative Risks of Breast and Ovarian Cancer among Mutation Carriers in Japanese Breast Cancer Families

Frequency of<i>BRCA1</i>and<i>BRCA2</i>Germline Mutations Detected by Protein Truncation Test and Cumulative Risks of Breast and Ovarian Cancer among Mutation Carriers in Japanese Breast Cancer Families

Frequency of BRCA1 and BRCA2 germline mutations in Japanese breast cancer families.

The purpose of this investigation is to study the frequency of BRCA1 and BRCA2 germline mutations in Japanese breast cancer families. Mutation analysis of BRCA1 and BRCA2 by SSCP was conducted on the 113 breast cancer patients (probands) with at least 1 breast cancer (site-specific breast cancer families, n = 101) or 1 ovarian cancer (breast/ovarian cancer families, n = 12) patient in their first-degree relatives. Fifteen deleterious mutations (13.3%), including 8 nonsense and 7 frameshift mutations, were identified in BRCA1, and 21 deleterious mutations (18.6%), including 8 nonsense, 12 frameshift and 1 splice-site mutations, were identified in BRCA2. In site-specific breast cancer families, mutation frequency of BRCA1 or BRCA2 was high in families with 3 or more breast cancer patients (36%, 9/25), early onset (40 < or = years old) breast cancer patients (38%, 19/50) or bilateral breast cancer patients (40%, 6/15). In breast/ovarian cancer families, mutations of BRCA1 (58.3%, n = 7), but not BRCA2 (0%, n = 0), were observed. BRCA1 codon 63 (TTA to TAA) nonsense mutation and BRCA2 frameshift mutation (5802 del AATT) were observed in 4 and 7 independent families, respectively. Haplotype analysis has suggested that carriers of each of these mutations have common ancestors. These results demonstrate that family profiles are important determinants of risk for carrying a BRCA1 or BRCA2 mutation and that cumulative frequency of BRCA1 and BRCA2 mutations in Japanese breast cancer families (31.9%) is within the range observed in Caucasian breast cancer families. Presence of Japanese founder mutations has also been suggested.

High proportion of missense mutations of the BRCA1 and BRCA2 genes in Japanese breast cancer families.

Mutations in either of two recently identified genes, BRCA1 and BRCA2, are thought to be responsible for approximately two-thirds of all cases of autosomal-dominantly inherited breast cancer. To examine the nature and frequency of BRCA1 and BRCA2 mutations in Japanese families exhibiting a high incidence of breast cancer, we screened 78 unrelated families in this category for mutations of these two genes. Examining the entire coding sequences as well as exon-intron boundaries of both genes by polymerase chain reaction (PCR) single-strand conformation polymorphism (SSCP) and multiplex-SSCP analysis, we identified possible disease-causing alterations in BRCA1 among affected members of 15 families and in BRCA2 in another 14 families. In 15 of those 29 families, the affected individuals carried missense mutations, although most germline mutations reported worldwide have been deletions or nonsense mutations. Our results, indicating that missense mutations of BRCA1 and BRCA2 tend to predominate over frameshifts or nonsense mutations in Japanese breast cancer families, will contribute significantly to an understanding of mammary tumorigenesis in Japan, and will be of vital importance for future genetic testing.

BRCA1 and BRCA2 Germline Mutations in Japanese with Hereditary Breast Cancer Families.

We examined germline mutations in BRCA1 and BRCA2 in 23 Japanese breast cancer families, using PCR-SSCP analysis. The same nonsense mutation (exon 5, Leu63ter) of BRCA1 was detected in two defferent families. Three different mutations resulting in a truncated BRCA2 protein (exon 9, 20, 24) were detected in three different families, including one male case of breast cancer. One base substitution mutation in BRCA2, A10462G, was detected in the other two families. Although the mean age of onset for breast cancer in families with the BRCA1-mutation was 50 years, the age of onset in families with the BRCA2-mutation was from 28 to 43 years. Among the 23 families examined, two families had members with ovarian cancers, three had members with prostate cancers, and one had a pancreatic cancer. However, none of these families was positive for the BRCA1 orBRCA2 mutation. Histopathologically, we observed a prevalence of histological grade 3 in BRCA1/2-associated familial breast cancers, because of nuclear atypia, structural atypia and mitotic activity. It is suggested that BRCA2 may play a more important role than BRCA1 in Japanese familial breast cancers, and these mutations are related to the aggressive nature and highly proliferative activity of the tumors.

BRCA2 germline mutations in Japanese breast cancer families.

Germline mutations of BRCA2 were examined in 20 Japanese breast cancer families without BRCA1 mutations, including one demonstrating cancer development in a male. Three different mutations, resulting in truncation of the BRCA2 protein, were detected in 3 different families. They were 9474insA (exon 24, termination at codon 3110), C8729A (exon 20, S2834 ter) and 982del4 (exon 9, termination at codon 275). The 982del4 mutation was detected in the family with a case of male breast cancer. Age at onset was young, with a range of 28-43 years, in the 2 female breast cancer families with truncation mutations. One probable missense mutation, A10462G (13412V), was further detected in 2 families, although cosegregation of this allele with the breast cancer phenotype was not complete. The rate of BRCA2 mutations in Japanese families was suggested to be almost the same as in Western countries, and larger than it is the case for BRCA1.

Linkage Analysis of BRCA1 in Japanese Breast Cancer Families

We examined the involvement of BRCA1, which plays a major role in Western breast cancer families, in Japanese breast cancer families. Eleven families, in which at least three individuals within third degree relatives were affected by breast cancer, were collected. Five of them were early‐onset breast cancer families, in which the average age at diagnosis was less than 45 years, and the other six were late‐onset families. Ovarian cancer was observed in one patient in the early‐onset families. Using seven polymorphic markers on chromosome 17q21, D17S250, ERBB2, THRA1, D17S579, D17S588, GIP and NME1, linkage to BRCA1 was analyzed. Linkage was not detected in any single family. Assuming homogeneity in an inherited component that confines the susceptibility to breast cancer in all families, we summed the LOD scores of all families. The cumulative LOD score obtained was –1.86 for D17S588 at θ= 0.001, indicating no linkage with BRCA1. Since the proportion of families linked to BRCA1 is larger in Western early‐onset breast cancer families than in late‐onset ones, we also summed the LOD scores of five early‐onset families. However, again a negative LOD score was obtained. These results suggest that BRCA1 is not a major breast cancer susceptibility gene in Japanese familial breast cancer.