ClinVar Genomic variation as it relates to human health

Variant summary: PALB2 c.495C>T alters a non-conserved nucleotide resulting in a synonymous change. 5/5 computational tools predict no significant impact on normal splicing. However, these predictions have yet to be confirmed by functional studies. The variant allele was found at a frequency of 0.00034 in 273862 control chromosomes, mainly in the Japanese population. The observed variant frequency is approximately 2.17 fold of the estimated maximal expected allele frequency for a pathogenic variant in PALB2 causing Hereditary Breast and Ovarian Cancer phenotype (0.00016), strongly suggesting that the variant is benign and likely to be a Japanese polymorphism. c.495C>T has been reported in the literature in a Japanese case-control study, where the variant was not statistically associated with breast cancer risk (Momozawa_2018). Co-occurrences with other pathogenic variant(s) have been reported (BRCA2 c.5576_5579delTTAA, internal data), providing supporting evidence for a benign role. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. Five ClinVar submissions from clinical diagnostic laboratories (evaluation after 2014) cite the variant four times as likely benign and once as uncertain significance. Based on the evidence outlined above, the variant was classified as benign.

This variant was observed in the ICSL laboratory as part of a predisposition screen in an ostensibly healthy population. It had not been previously curated by ICSL or reported in the Human Gene Mutation Database (HGMD: prior to June 1st, 2018), and was therefore a candidate for classification through an automated scoring system. Utilizing variant allele frequency, disease prevalence and penetrance estimates, and inheritance mode, an automated score was calculated to assess if this variant is too frequent to cause the disease. Based on the score, this variant could not be ruled out of causing disease and therefore its association with disease required further investigation. A literature search was performed for the gene, cDNA change, and amino acid change (if applicable). No publications were found based on this search. This variant was therefore classified as a variant of unknown significance for this disease.

This variant is considered benign. This variant is a silent/synonymous amino acid change and it is not expected to impact splicing.

This alteration is classified as likely benign based on a combination of the following: seen in unaffected individuals, population frequency, intact protein function, lack of segregation with disease, co-occurrence, RNA analysis, in silico models, amino acid conservation, lack of disease association in case-control studies, and/or the mechanism of disease or impacted region is inconsistent with a known cause of pathogenicity.

Curators: Marc Tischkowitz, Arleen D. Auerbach. Submitter to LOVD: Yukihide Momozawa.

The PALB2 p.Gly165= variant was not identified in the literature nor was it identified in the Cosmic, MutDB, LOVD 3.0, or Zhejiang Colon Cancer Databases. The variant was identified in the following databases: dbSNP (ID: rs200937538) “With Likely benign allele”, ClinVar (classified likely benign by Ambry Genetics and GeneDx), Clinvitae (2x) and in control databases in 4 of 246210 chromosomes at a frequency of 0.00002 (Genome Aggregation Database Feb 27, 2017). It was observed in the East Asian population in 4 of 17248 chromosomes (freq: 0.0002); it was not observed in the African, Other, Latino, European Non-Finnish, Ashkenazi Jewish, European Finnish, and South Asian populations. The p.Gly165= variant is not expected to have clinical significance because it does not result in a change of amino acid and is not located in a known consensus splice site. The variant occurs outside of the splicing consensus sequence and 2 of 5 in silico or computational prediction software programs (SpliceSiteFinder, MaxEntScan, NNSPLICE, GeneSplicer, HumanSpliceFinder) predict a greater than 10% difference in splicing; this is not very predictive of pathogenicity. In summary, based on the above information the clinical significance of this variant cannot be determined with certainty at this time. This variant is classified as a variant of uncertain significance.