Pathogenic Research Of PALB2 Gene Missense Mutation C.1955G>A In A Familial Prostate Cancer

Objective:Report of a prostate cancer family in the Chinese Han Population,and the homologous recombination repair（HRR）gene screening of the three patients all detected the presence of the PALB2 c.1955G>A germline variant,which is rare in the population and its clinical significance is currently unknown.We will comprehensively assess whether this mutation is an important cause of prostate cancer in this family according to the guidelines for the interpretation of sequence variants established by The American College of Medical Genetics and Genomics（ACMG）.In order to better understand of prostate cancer pathogenic genes,and provide suggestion for future genetic counseling and follow-up treatment of this family.Methods:（1）Genetic counseling was conducted for the family,DNA was extracted from peripheral blood for Sanger sequencing to verify mutations,and mutation detection was performed on family members to improve family information.（2）Silico bioinformatics tools for pathogenic predictive analysis of mutations.（3）Lymphocytes were extracted from peripheral blood using lymphocyte separation medium to extract RNA and total protein,respectively.The expression of PALB2 gene in probands and healthy controls was compared by qPCR and Western blot experiments.（4）Tumor paraffin section specimens from the proband were used to assess homologous recombination function.Statistical analysis was performed using GraphPad Prism Version 9.0,and the two groups of samples were compared using an unpaired t-test,and P<0.05 was considered statistically significant.Results:（1）The family proband Ⅱ₇,a 79-year-old male,was first diagnosed with prostate cancer more than one years ago due to "dysuria",and then Ⅱ₃and Ⅱ₅were diagnosed successively due to "urination symptoms".HRR gene testing in all three patients found PALB2 c.1955G>A germline variation,which was manifested as heterozygous nucleotide variation in the coding region of gene exon 5,which resulted in the change of nucleotide position 1955 from guanine to adenine and amino acid position 652 from serine to asparagine.Ⅲ₃and Ⅲ₆were confirmed as c.1955G>A mutation carriers,and the rest of their family members did not undergo mutation screening,and had no relevant clinical symptoms,and no abnormality was found in laboratory examination;（2）Five prediction tools（Polyphen-2,SIFT,MutationAssessor,PROVEAN,and MutationTaster）showed that this variant did not have a significant effect on the protein,and this variant appeared outside the splicing common sequence.And only one of the four computer prediction software programs（SpliceSiteFinder,MaxEntScan,NNSPLICE,and GeneSplicer）predicted splicing differences greater than 10%;（3）The expression of PALB2 mRNA（1.09±0.27 vs 1.02±0.18,P=0.67）and PALB2 protein（0.64±0.02 vs 0.66±0.08,P=0.76）in mutation carriers was not significantly different from that in healthy controls;（4）Immunofluorescence staining of paraffin sections of the proband’s tumor did not find homologous recombination defects（HRD）,RAD51-FFPE score of 42%（>15%）.Conclusion:PALB2 c.1955G>A tends to be a benign mutation that does not result in homologous recombination dysfunction,and patients in this family may not benefit from treatment with PARP inhibitors.