PVS1 Antibody

What is the PVS1 criterion in the ACMG/AMP guidelines?

The PVS1 criterion is the only element in the 2015 ACMG/AMP sequence variant interpretation guidelines that carries a "Very Strong" pathogenicity weight. It was defined for "null variant (nonsense, frameshift, canonical ±1 or 2 splice sites, initiation codon, single or multi-exon deletion) in a gene where loss-of-function (LoF) is a known mechanism of disease" . When properly applied, this criterion significantly impacts variant classification, as a combination of PVS1 with only one moderate or two supporting pathogenicity criteria can lead to a likely pathogenic or pathogenic classification, respectively .

Why is accurate interpretation of PVS1 critical for research applications?

Accurate PVS1 interpretation is critical because null variants are prevalent within the human genome (at least 100 per genome) and are markedly enriched in low-frequency alleles . These variants often meet the PM2 criterion (moderate evidence for pathogenicity based on low frequency) in the ACMG/AMP guidelines. The combination of PVS1_VeryStrong and PM2 could easily reach a likely pathogenic classification, which would lead to actionable clinical interventions . Misapplication of PVS1 could therefore result in misclassification of variants and potentially inappropriate clinical management decisions.

What types of genetic variants can PVS1 be applied to?

PVS1 can be applied to several types of predicted loss-of-function variants, including:

• Nonsense variants

• Frameshift variants

• Canonical ±1 or 2 splice site variants

• Initiation codon variants

• Single or multi-exon deletions

• Whole gene deletions

Each variant type requires specific considerations regarding its location, potential impact on protein function, and the disease mechanism for appropriate application of PVS1.

How should researchers evaluate if loss-of-function is a disease mechanism for a gene?

Researchers should consider the following criteria to determine if loss-of-function is an established disease mechanism for a specific gene:

The gene should have a Strong or Definitive clinical validity level for the disease association (as per ClinGen framework) before applying PVS1 . Additionally, researchers should verify that loss-of-function is indeed the established disease mechanism, rather than gain-of-function or other mechanisms.

What is nonsense-mediated decay (NMD) and how does it impact PVS1 application?

Nonsense-mediated decay (NMD) is a surveillance pathway that selectively degrades nonsense mRNAs, observed in all eukaryotes to date . For PVS1 application, NMD is generally considered active when a premature termination codon occurs in any exon except the last exon or within the last 50 nucleotides of the penultimate exon .

The NMD prediction significantly impacts PVS1 strength assignment:

• If NMD is predicted to occur, a stronger level of PVS1 may be applied

• If NMD is not predicted (e.g., variant in the last exon), additional evidence about the functional impact of the truncated protein is required

Researchers should always assess NMD prediction as a first step when evaluating nonsense and frameshift variants for PVS1 application .

How do variant-specific features modify the strength level of PVS1?

The ClinGen SVI Working Group has established that not all putative LoF variants have equal strengths, and the PVS1 strength level can vary depending on the available evidence for each variant type . The strength levels include:

Variant-specific features that may lead to downgrading include:

• Variant location in a non-critical region of the protein

• Variant affecting an exon that may be alternatively spliced

• Uncertain impact on protein function

• Exon skipping potential

• Variant located near the 3' end of the gene

How should researchers interpret initiation codon variants using PVS1?

Functional studies have shown that start re-initiation can be robust, occurring at alternate ATG or non-ATG sites downstream and even upstream of the original start site . Therefore, the SVI Working Group generally does not recommend assigning PVS1 or PVS1_Strong for start loss variants.

Researchers should follow these guidelines:

• If alternative functional gene transcripts use an alternative start codon, do not apply PVS1 at any strength level

• If no alternative start codons exist in the transcript set:

  • Apply PVS1_Moderate if one or more pathogenic variant(s) have been reported 5' of the next downstream in-frame start codon (Methionine)

  • Apply PVS1_Supporting if no pathogenic variant(s) occur upstream of the new Methionine

A more quantitative approach suggests:

• PVS1_VeryStrong: >6 upstream pathogenic/likely pathogenic variants

• PVS1_Strong: 3-6 upstream pathogenic/likely pathogenic variants

• PVS1_Moderate: 1-2 upstream pathogenic/likely pathogenic variants

What specific considerations apply to the interpretation of splice site variants?

When evaluating canonical ±1,2 splice site variants, researchers should consider:

• Predicted effect on reading frame and NMD

• Inclusion of the affected exon in biologically relevant transcripts

• Potential for exon skipping

• Presence of in-frame alternate splice sites

If the splice variant is predicted to cause exon skipping resulting in an in-frame deletion, researchers should determine if the removed portion is critical to protein function . If the exon isn't essential or the variant might use an alternate splice site, PVS1 strength should be downgraded accordingly.

How can automated tools improve PVS1 interpretation?

Automated tools like AutoPVS1 can facilitate consistent and accurate interpretation of predicted loss-of-function variants. These tools:

• Apply specific criteria for each variant type

• Consider disease mechanism implications

• Evaluate NMD classification

• Select biologically relevant transcripts

• Assess the importance of truncated regions

• Determine clinical significance of exons

• Identify cryptic or newly generated splice sites

• Predict potential in-frame start codons

AutoPVS1 has demonstrated high accuracy and reproducibility, with particular value in the interpretation of splicing variants. Research shows that 40.7% of splicing variants were assigned a decreased PVS1 strength level, significantly higher than frameshift and nonsense variants .

How should researchers handle whole gene deletions in PVS1 interpretation?

Whole gene deletions default to full PVS1 strength, assuming the gene meets the criteria for a LoF disease mechanism . Although application of PVS1 alone would not reach a Pathogenic or Likely pathogenic classification using the combining rules in Richards et al. 2015, the SVI working group acknowledged that for a full gene deletion of a known haploinsufficient gene, a Pathogenic classification is warranted as long as there is no conflicting evidence that would question the technical data or haploinsufficiency mechanism .

In the Bayesian SVI formulation, a very strong criterion alone generates a posterior probability of 0.975, which falls in the likely pathogenic range . This provides statistical justification for the classification approach to whole gene deletions.

How can researchers evaluate if an exon is biologically relevant for PVS1 interpretation?

Researchers should assess the biological relevance of an exon through multiple approaches:

• Functional evidence from literature

• Expression patterns from databases like GTEx (https://www.gtexportal.org/home/)

• Presence of previously established pathogenic variants in the exon

• Analysis of alternative splicing and exon skipping patterns

An exon may not be biologically relevant if it is:

• Missing from alternative biologically relevant transcripts

• Enriched for high-frequency LoF variants in the general population

In such cases, PVS1 at any strength level should not be applied to variants affecting these exons .

How does the region-specific impact affect PVS1 interpretation for variants near the 3' end?

For variants near the 3' end of a gene that escape NMD, researchers should consider:

• Evidence from functional studies on the importance of the C-terminal region

• Presence of known pathogenic variants in the region

• Critical functional domains in the affected region

If there is evidence indicating the truncated region is critical to protein function, PVS1_Strong is appropriate . Without such evidence, the length of the missing region factors into decision-making:

• 10% of protein product missing: PVS1_Strong

• <10% of protein product missing: PVS1_Moderate

The SVI Working Group acknowledges that empirical data are needed to further refine these generic rules, and disease-specific groups should specify based on expert knowledge of their genes of interest .

What are the key considerations when applying PVS1 to multi-exon deletions?

When evaluating multi-exon deletions, researchers should consider:

• Reading frame effects

• NMD predictions

• Biological relevance of affected exons

• Critical domains impacted

The reading frame and NMD considerations that apply to splice variants and nonsense/frameshift variants are also applicable to multi-exon deletions . Researchers should follow the decision tree developed by the SVI Working Group to determine the appropriate PVS1 strength based on these factors.