Identification of Two Novel HOXB13 Germline Mutations in Portuguese Prostate Cancer Patients

Abstract

The HOXB13 germline variant G84E (rs138213197) was recently described in men of European descent, with the highest prevalence in Northern Europe. The G84E mutation has not been found in patients of African or Asian ancestry, which may carry other HOXB13 variants, indicating allelic heterogeneity depending on the population. In order to gain insight into the full scope of coding HOXB13 mutations in Portuguese prostate cancer patients, we decided to sequence the entire coding region of the HOXB13 gene in 462 early-onset or familial/hereditary cases. Additionally, we searched for somatic HOXB13 mutations in 178 prostate carcinomas to evaluate their prevalence in prostate carcinogenesis. Three different patients were found to carry in their germline DNA two novel missense variants, which were not identified in 132 control subjects. Both variants are predicted to be deleterious by different in silico tools. No somatic mutations were found. These findings further support the hypothesis that different rare HOXB13 mutations may be found in different ethnic groups. Detection of mutations predisposing to prostate cancer may require re-sequencing rather than genotyping, as appropriate to the population under investigation.

Fig 1. Pedigrees and Sanger sequencing electropherograms of patients from early-onset and familial/hereditary PrCa families.

Pedigrees and electropherograms of patient HPC311 with the HOXB13 p.(Ala128Asp), c.383C>A variant (A) and patient HPC169 with the HOXB13 p.(Phe240Leu), c.720C>A variant (B). The index case and the position of each mutation are indicated by an arrow.

Fig 2. Pedigree and Sanger sequencing electropherograms of the patient from the prostate carcinoma series.

Pedigree (A) and electropherograms of patient P308T obtained from tumor (B) and from blood (C) show the presence of the HOXB13 c.383C>A, p.(Ala128Asp) variant in heterozygosity. The index case and the mutation are indicated by an arrow.

Fig 3. Clustal W2 alignment of the human HOXB13 protein and its orthologues in selected species.

The amino acids residues predicted to be changed by both missense mutations identified in this study [p.(Ala128Asp) and p.(Phe240Leu)] are highlighted by grey shaded boxes and residue 84 predicted to be affected by the previously described G84E mutation is highlighted by a grey box.

Fig 4. HOXB13 structure and distribution of coding non-synonymous variants reported in prostate cancer patients.

The homeobox protein Hox1A3 N-terminal domain (PF12284) and the homeobox domain (PF00046) are represented as an orange box inside each of the corresponding exons (homeobox protein Hox1A3 N-terminal domain: residues 21–123; homeobox domain: residues 217–273). Variants located within these domains are shown above the corresponding domain. Both missense variants found in our patients [p.(Ala128Asp) and p.(Phe240Leu)] are shown in red. Variants described by other authors are shown in black.