Genomic rearrangements of the BRCA1 gene in Chilean breast cancer families: an MLPA analysis.

Point mutations and small deletions and insertions in BRCA1 and BRCA2 genes are responsible of about 20% of hereditary breast cancer cases in Chilean population. Studies in other populations have identified the amplification and/or deletion of one or more exons in these genes as the cause of the disease. In this study the authors determined the presence of these types of alterations in BRCA1 and BRCA2, in 74 Chilean families with breast/ovarian cancer that were negative for germline mutations in these genes. Since these alterations are not detectable using the conventional PCR-based methods, the authors use MLPA (multiplex ligation-dependent probe amplification) to detect amplifications and/or deletions in BRCA1 and BRCA2 genes. The authors identified two different alterations in BRCA1: exon 10 duplication in one family and amplification of exons 3, 5, and 6 in two families. Duplication of exon 10 contains intronic adjacent sequences suggesting gene duplication. The second rearrangement consist of a 4 times amplification of a fragment containing exons 3, 5, and 6 joined together with no introns, suggesting the presence of a processed pseudogene. No alterations were detected in BRCA2. In order to validate the MLPA results and characterize the genomic alterations the authors performed qPCR, long range PCR, and sequencing.

Promoter hypermethylation of BRCA1 correlates with absence of expression in hereditary breast cancer tumors.

Germline mutations in BRCA1 account for a low proportion of hereditary cases in diverse populations. Several efforts have been made to find new genes involved in the inheritance of breast cancer with no success until today. The participation of BRCA1 in the development of breast cancer has been proposed in several studies where hypermethylation of its promoter and a decrease in expression has been reported for sporadic cases and one study on familial cases. To explore the participation of BRCA1 in hereditary carcinogenesis through a different mechanism than the inheritance of germline mutations, we studied the methylation status of its promoter in breast tumors, from patients previously screened for BRCA1/BRCA2 germline mutations. We also determined the presence of the BRCA1 protein in these tumors and correlated both events with tumor grade, hormone receptors and ERBB2 presence. Promoter hypermethylation of the BRCA1 gene was detected in 51% of our biopsies, among which 67% did not express the respective protein. This result leads us to suggest that hypermethylation could be considered as an inactivating mechanism for BRCA1 expression, either as a first or second hit. Moreover, a number of biopsies with absence of expression on BRCA1 showed negative detection of estrogen and progesterone receptors, a similar phenotype to BRCA1 mutated breast tumors.

Myotonic dystrophy in a female with myasthenia gravis.

The likelihood of coexistence in the same patient of myasthenia gravis and myotonic dystrophy has been estimated at 1 in 40 million. The case of a patient in whom both diagnoses were made is reported here. A 13-year-old girl was diagnosed with myasthenia gravis because of weakness, fluctuating fatigability, and mild difficulty with chewing and swallowing. She had ptosis, with weakness predominantly of her face, arms, and neck. Serum antibodies against acetylcholine receptors were 9.9 nmol/L. She was started on pyridostigmine, with significant clinical improvement, reassuming normal daily activities. Two years later, generalized weakness reappeared and reappraisal of her symptomatology disclosed tongue percussion and hand action myotonia. Molecular genetic analysis disclosed 550 repeats of cytosine-thymidine-guanosine triplets on the DMPK gene. Undiagnosed relatives had expansions ranging from 110 to 1000 repeats. Myotonic dystrophy is considered the most common muscular dystrophy, with highly variable clinical manifestations; mildly affected individuals may escape clinical detection. Myasthenia gravis has an estimated prevalence of 15 per 100,000. No studies on the epidemiology of these diseases have been done in Chile. Although both diseases have specific clinical and laboratory presentations, they share some features in the mode of presentation that may generate difficulty in diagnosis of both entities in the same patient.

Incidence of BRCA1 and BRCA2 mutations in 54 Chilean families with breast/ovarian cancer, genotype-phenotype correlations.

Our aim was to analyze the incidence of mutations in BRCA1 and BRCA2 genes in 54 families with breast/ovarian cancer. Families were selected from three Institutions following the standard criteria for hereditary breast/ovarian cancer. PCR amplification of all exons was performed, followed by SSCP, heteroduplex, PTT and sequencing analysis. We identified eight truncation mutations, three in the BRCA1 gene and five in the BRCA2 gene. Three of these mutations have not been reported previously by other groups: 308insA in one family, 3936 C>T in two families, for BRCA1, and 4970insTG in one family for BRCA2. In addition two families having Ashkenazi Jewish ancestors present the well known mutations 185delAG and 6174delT. Interestingly, 5 out of 11 families have mutations recurrent in Spanish families. Among the 54 families selected, seven have breast and ovary cancer cases, and only two presented a mutation in BRCA1 or BRCA2 genes. Other cancers as prostate and stomach are frequent among relatives carrying the mutation. Five cases of very early onset (<31 years old) breast cancer were detected. The frequencies of BRCA1 (0.074) and BRCA2 (0.13) mutations in our families is low but similar to the incidence found in other populations, like in Spain. Since is widely known that risk factors that modulate the development of breast cancer such as lifestyle risk factors, geographic location, country of origin and socioeconomic status, besides a familial history of breast cancer our findings suggest that the history of colonization and immigrations is very relevant when studying hereditary factors associated to breast cancer.

[Determination of a BRCA1 gene mutation in a family with hereditary breast cancer]. / Determinación de una mutación en el gen BRCA1 en una familia que presenta cáncer de mama hereditario.

BACKGROUND: Breast cancer is the main cause of death among women between 40 and 55 years old, in whom the hereditary cases are common. Therefore, the molecular diagnosis of germ line mutations involved in breast cancer susceptibility is relevant. BRCA1 and BRCA2 have been described as the two major genes involved in familial breast/ovarian cancer. We are performing a screening of BRCA1 and BRCA2 genes, in a group of 50 high risk Chilean families for breast/ovarian cancer. We have detected a mutation, 3936 C>T, that leads to a truncated protein, in two affected women from one of the families in study. AIM: To report the results of the screening for 3936 C>T in healthy relatives of index women. MATERIAL AND METHODS: The molecular diagnosis of this mutation was offered to the healthy members of this family, and 17 relatives accepted to be tested. The region of the BRCA1 gene that includes the 3936 C>T mutation, was analyzed through PCR amplification, digestion with restriction enzyme BstNI, and direct sequencing. RESULTS: 3936 C>T DNA mutation was present in 8 relatives. CONCLUSIONS: Considering the high risk of having a mutation in the BRCA1 gene, specially in pre-menopausal women, the molecular diagnosis, genetic and clinical counseling are highly relevant. In Chile the molecular diagnosis is still not widely applied.