When ACMG and ClinVar Interpretations Contradict: Which One Should Be Followed?

In clinical germline genetic testing, it is not uncommon to encounter situations where the variant classification in ClinVar differs from the classification determined using ACMG guidelines. This can create confusion for clinicians, laboratories, and patients.

The key principle to understand is that ACMG guidelines represent the internationally accepted framework for variant interpretation, while ClinVar is a database that aggregates interpretations from multiple submitters. Therefore, they serve different purposes in clinical genomics.

The Short Answer

When there is a contradiction:

The laboratory should follow its own ACMG-based interpretation rather than relying solely on ClinVar.

ClinVar should be considered supporting evidence, not the final authority for variant classification.

Why ClinVar and ACMG May Disagree

Several reasons can explain discrepancies between ClinVar entries and ACMG-based interpretations.

1. Different Evidence Available

Some ClinVar submissions may be based on older literature or limited data, while a laboratory performing interpretation today may have access to:

• New population databases (e.g., gnomAD updates)

• New functional studies

• Additional case reports

• Internal laboratory evidence

As knowledge evolves, variant classifications may change.

2. Variability Between Laboratories

ClinVar aggregates data from many laboratories worldwide, each with:

• Different interpretation pipelines

• Different evidence weighting

• Different timepoints of submission

This may lead to conflicting classifications within ClinVar itself (e.g., one lab reporting “Pathogenic” while another reports “VUS”).

3. Updates to ACMG Criteria

Since the original ACMG/AMP 2015 guidelines, many refinements have been introduced through ClinGen expert panels and disease-specific interpretation rules.

A laboratory using updated criteria may reach a different conclusion from older ClinVar submissions.

How Clinical Laboratories Should Handle Conflicts

Most accredited clinical laboratories follow a structured approach.

Step 1: Perform Internal ACMG Classification

The variant should first be evaluated using:

• ACMG/AMP criteria

• Population frequency databases

• Functional evidence

• Segregation data

• Published literature

This produces the laboratory’s primary classification.

Step 2: Review ClinVar as Supporting Evidence

ClinVar can then be used to check:

• Whether the variant has been reported previously

• Consensus among laboratories

• Supporting publications

• Expert panel classifications

If ClinVar contains ClinGen expert panel review, this evidence is usually given higher confidence.

Step 3: Document Discrepancies

If ClinVar classifications differ, the laboratory should:

• Document the discrepancy

• Evaluate the evidence behind each submission

• Provide justification for the final classification

This is important for quality management and audit compliance (e.g., ISO15189 or CAP laboratories).

When ClinVar Should Be Taken More Seriously

Certain ClinVar entries carry stronger authority.

ClinGen Expert Panel Reviewed Variants

Variants curated by ClinGen Variant Curation Expert Panels (VCEP) follow ACMG rules with disease-specific refinements. These classifications often represent the most reliable interpretations available.

Multiple Concordant Submissions

If many independent laboratories report the same classification, this increases confidence in the interpretation. However, even then, the final decision still lies with the reporting laboratory.

What International Best Practice Recommends

International clinical genetics practice generally follows this hierarchy:

1. ACMG/AMP variant interpretation framework (primary system)2. ClinGen expert panel curated variants3. ClinVar aggregated interpretations4. Internal laboratory evidence and databases

This ensures variant classifications are systematic, transparent, and reproducible.

Example Scenario

A variant in BRCA1 may appear as:

Source	Classification
ClinVar submission (2017)	Likely pathogenic
ClinVar submission (2020)	VUS
Laboratory ACMG interpretation (2026)	VUS

In this case, the laboratory should report VUS, because the available evidence no longer supports pathogenicity under current ACMG criteria.

Why This Matters for Patients

Variant classification directly affects clinical decisions such as:

• Cancer surveillance

• Preventive surgery

• Family testing

• Treatment choices

Overcalling a variant as pathogenic when evidence is insufficient can lead to unnecessary anxiety and medical interventions.

Conversely, failing to recognize a pathogenic variant can miss opportunities for prevention or treatment.

This is why standardized frameworks like ACMG guidelines are essential.

Final Takeaway

When ACMG interpretation and ClinVar entries contradict:

ACMG-based interpretation performed by the reporting laboratory should take precedence.

ClinVar remains a valuable knowledge resource, but it should not replace structured variant interpretation using internationally accepted clinical guidelines.