Analysis of Italian BRCA1/2 Pathogenic Variants Identifies a Private Spectrum in the Population from the Bergamo Province in Northern Italy

Abstract

Germline pathogenic variants (PVs) in the BRCA1 or BRCA2 genes cause high breast cancer risk. Recurrent or founder PVs have been described worldwide including some in the Bergamo province in Northern Italy. The aim of this study was to compare the BRCA1/2 PV spectra of the Bergamo and of the general Italian populations. We retrospectively identified at five Italian centers 1019 BRCA1/2 PVs carrier individuals affected with breast cancer and representative of the heterogeneous national population. Each individual was assigned to the Bergamo or non-Bergamo cohort based on self-reported birthplace. Our data indicate that the Bergamo BRCA1/2 PV spectrum shows less heterogeneity with fewer different variants and an average higher frequency compared to that of the rest of Italy. Consistently, four PVs explained about 60% of all carriers. The majority of the Bergamo PVs originated locally with only two PVs clearly imported. The Bergamo BRCA1/2 PV spectrum appears to be private. Hence, the Bergamo population would be ideal to study the disease risk associated with local PVs in breast cancer and other disease-causing genes. Finally, our data suggest that the Bergamo population is a genetic isolate and further analyses are warranted to prove this notion.

Keywords: BRCA1; BRCA2; Bergamo province; Italy; breast cancer; pathogenic variants; spectrum.

Figure 1

Ln odds ratio (ORs) and 95% confidence intervals (CIs) of the 20 PVs found in both the 100 BGP and the 919 non-BGP carriers. For each PV, the carrier frequency (%) is reported; the ln (OR) and the 95% CI are indicated by dots and horizontal lines, respectively. The ORs were estimated by univariate logistic model. The joint OR (ln OR = 3.61 (95% CI = 2.83–4.39) obtained by considering all the 20 PVs, is also showed.