Alexandr A. Romanko

5’UTR gene regions in germline DNA sequencing panels: lessons from the analysis of breast and ovarian cancer patients of Tatar and Bashkir ethnic origin

Tatars and Bashkirs are large and closely related ethnic communities that reside in the territory of the Russian Federation but have managed to preserve their national identity through the course of history. This study included 446 Tatars, 53 Bashkirs, and 26 women of mixed Tatar-Bashkir ethnicity. Germline DNA analysis was performed for 349 breast cancer (BC) patients with clinical features of hereditary disease (family history, or young onset ( T, was observed in 11 subjects. Among 27 women with BRCA2 PVs, six and five women were carriers of the c.-39-1_-39del and c.468dup variants, respectively. The loss-of-heterozygosity (LOH) test confirmed the pathogenic nature of the c.-39-1_-39del [rs758732038] allele, which is located in the 5'UTR of BRCA2. Analysis of other BC-associated genes revealed single instances of PVs affecting PALB2, TP53, ATM, RAD51, and RAD51D genes. Tatars and Bashkirs, which are ethnically and religiously separated from Russians, carry an unexpectedly high proportion of Slavic BRCA1/2 founder alleles. The identification of recurrent Tatar/Bashkir BRCA2 pathogenic 5'UTR variant c.-39-1_-39del calls for a systematic analysis of regulatory regions of cancer-predisposing genes in patients with missing heritability.

Ethnicity-specific BRCA1, BRCA2, PALB2, and ATM pathogenic alleles in breast and ovarian cancer patients from the North Caucasus

Mountain areas of the North Caucasus host several large ethnic communities that have preserved their national identity over the centuries. This study involved high-grade serous ovarian cancer (HGSOC) and breast cancer (BC) patients from Dagestan (HGSOC: 37; BC: 198), Kabardino-Balkaria (HGSOC: 68; BC: 155), North Ossetia (HGSOC: 51; BC: 104), Chechnya (HGSOC: 68; BC: 79), Ingushetia (HGSOC: 19; BC: 103), Karachay-Cherkessia (HGSOC: 13; BC: 47), and several Armenian settlements (HGSOC: 16; BC: 101). The group of BC patients was enriched by young-onset and/or family history-positive and/or bilateral and/or receptor triple-negative cases. The entire coding region of BRCA1, BRCA2, PALB2, and ATM genes was analyzed by next-generation sequencing. A significant contribution of BRCA1/2 pathogenic variants (PVs) to HGSOC and BC development was observed across all North Caucasus regions (HGSOC: 19-39%; BC: 6-13%). Founder alleles were identified in all ethnic groups studied, e.g., BRCA1 c.3629_3630delAG in Chechens, BRCA2 c.6341delC in North Ossetians, BRCA2 c.5351dupA in Ingush, and BRCA1 c.2907_2910delTAAA in Karachays. Some BRCA1/2 alleles, particularly BRCA2 c.9895C > T, were shared by several nationalities. ATM PVs were detected in 14 patients, with c.1673delG and c.8876_8879delACTG alleles occurring twice each. PALB2 heterozygosity was observed in 5 subjects, with one variant seen in 2 unrelated women. This study adds to the evidence for the global-wide contribution of BRCA1/2 genes to HGSOC and BC morbidity, although the spectrum of their PVs is a subject of ethnicity-specific variations. The data on founder BRCA1/2 alleles may be considered when adjusting the BRCA1/2 testing procedure to the ethnic origin of patients.