Between 5 % and 10 % of breast cancer cases are hereditary, arising because the patient inherits from the father or mother a mutation in a gene that is susceptible to causing the illness. BRCA1 and BRCA2 have already been identified as two of the genes to be monitored. It is estimated that 30 % of hereditary breast cancer cases are due to mutations in one of these two genes (which suggests, at the same time, that there are other genes involved, but exactly how is still unknown). In any case, few of the mutations found in BRCA1 and BRCA2 could be clearly identified as pathological. The fact is that the mutations found were numerous; their variation even depending on the population.
Biologist Elena Beristain has been investigating the CAPV-EAE population. Concretely, for her study she took 521 patients mainly from the Txagorritxu hospital in the Basque capital city of Vitoria-Gasteiz, and the Cruces hospital in Barakaldo, near Bilbao: 274 patients with breast or ovarian cancer (given that the latter is also associated with mutations in the BRCA1 and BRCA2 genes), 115 family relations of these, and another 132 women who acted as a control population. Ms Beristain molecularly characterised the BCRA1 y BCRA2 genes of these individuals; apart from the exon 10 of the CHEK2 gene, also associated with the illness. Her thesis was defended at the University of the Basque Country (UPV/EHU) and it is entitled, Genetic study amongst women resident in the CAPV-EAE with hereditary breast/ovary cancer.
Could rise to 12 %
According to the results shown, different types of variations in the genes under study have been found, including pathological ones, neutral ones and those of uncertain significance. As regards the clearly pathological mutations, the frequency is 10 %. Nevertheless, Ms Beristain stressed that, amongst those sporadic cases of under-40s, that is a especially rare condition: only in one case was a pathological mutation found. This is why she suggested discarding under-35s in this type of research, and in which case the result arrived at in her study rises from 10 % to 12 %. In any case, the percentages of pathological mutations found in this genetic study of the CAPV-EAE population turned out to be less than amongst other European populations.
The study has thrown up more data regarding age. For example, the percentages show that, for family-member carriers of mutation in the main genes under study, the accumulated risk of suffering breast cancer at 70 is 69 % for the BRCA1 and 67 % for the BRCA2. This means that penetration is not complete and there exists the possibility that this gene does not, in the end, express itself. As regards the data on gender, it is significant that masculine breast cancer is mainly associated with mutations in the BRCA2 gene.
Different mutations in the Autonomous Community of the Basque Country
The variability from population to population in mutations in general is also clear from the results of this thesis. Ms Beristain explained that a great number of alterations, hitherto unrecorded, have been found, and from this she concludes that many of the mutations found in the CAPV-EAE are different from those described for other populations. However, she explains, amongst these, no founder effect mutation was found, i.e. there has been no case of some, many or all Basque patients coming from a small population of individuals having transmitted this common genetic characteristic to all their descendents. However it may be, the new types of mutations found represent a contribution to the already existing variability.
About the author
Elena Beristain Mendizabal (Eibar, 1978) is a biology graduate from the University of Malaga and doctor in biology from the UPV/EHU. She defended her PhD thesis at the Department of Genetics, Physical Anthropology and Animal Physiology of the Faculty of Science and Technology (UPV/EHU), and drew it up under the direction of doctor María Isabel Tejada Minués, Head of the Molecular Genetics Laboratory of the Department of Biochemistry at the Cruces Hospital (Barakaldo). It is here that she carried out the main part of her thesis, but she also collaborated with the Service of Pathological Anatomy at the Txagorritxu Hospital, with the Oncological Research Centre (CNIO) in Madrid and with other teams from the Spanish Consortium for Hereditary Breast Cancer. Currently Ms Beristain is technical research assistant at the Research Unit at Cruces Hospital.