Germline Genetic Test Reporting: Should Laboratories Follow ClinVar or ACMG Guidelines?

The rapid adoption of next-generation sequencing (NGS) has dramatically increased the number of genetic variants detected in clinical testing. However, identifying a variant is only the first step—the critical challenge lies in interpreting and reporting its clinical significance.

One common question among laboratories and clinicians is whether germline variant interpretation should follow ClinVar classifications or ACMG guidelines. While both are essential tools in modern genomic medicine, they serve very different roles. Understanding their differences is crucial for ensuring accurate and clinically responsible genetic test reporting.

Understanding Germline Variant Interpretation

A germline variant is a genetic alteration present in the egg or sperm and therefore inherited by offspring. These variants can cause hereditary diseases or influence drug response and health risks.

Because sequencing technologies can detect thousands of variants per individual, standardized frameworks are required to determine which variants are clinically meaningful.

The ACMG Guidelines: The International Standard

What are ACMG Guidelines?

The American College of Medical Genetics and Genomics (ACMG) together with the Association for Molecular Pathology (AMP) published widely adopted standards for sequence variant interpretation in 2015.

These guidelines provide a structured, evidence-based system to evaluate genetic variants using multiple types of evidence.

Five-Tier Variant Classification System

ACMG recommends classifying variants into five categories:

1. Pathogenic

2. Likely pathogenic

3. Variant of uncertain significance (VUS)

4. Likely benign

5. Benign 

To determine these classifications, ACMG defines 28 evidence criteria covering:

• Population frequency

• Computational predictions

• Functional studies

• Segregation data

• Case reports

• Previously established pathogenic variants

Each piece of evidence is weighted (very strong, strong, moderate, supporting) and combined using defined rules to reach a final classification.

Advantages of ACMG Guidelines

1. Internationally accepted standard - ACMG-AMP guidelines are recognized globally as the standard framework for clinical variant interpretation.

2. Evidence-based classification - Each variant classification is supported by defined criteria and documented evidence.

3. Consistent clinical reporting - Standard terminology ensures consistency across laboratories.

4. Regulatory acceptance - Many accredited clinical laboratories (ISO15189, CAP, CLIA) require or strongly recommend ACMG-based variant interpretation.

ClinVar: A Global Variant Database

What is ClinVar?

ClinVar is a public database hosted by the National Center for Biotechnology Information (NCBI) that aggregates information about genetic variants and their relationship to human health.

ClinVar collects variant interpretations submitted by:

• Clinical laboratories

• Research institutions

• Expert panels

• Databases

It stores both the variant classification and the supporting evidence.

Key Features of ClinVar

• Public repository of millions of variants

• Aggregated interpretations from multiple laboratories

• Evidence and references linked to each variant

• Ability to compare classifications across submitters

ClinVar can also display aggregate classifications when multiple submitters have evaluated the same variant.

Key Differences Between ACMG Guidelines and ClinVar

Feature	ACMG Guidelines	ClinVar
Type	Interpretation framework	Variant database
Purpose	Standardize variant classification	Share variant interpretations
Authority	Professional clinical guideline	Data repository
Evidence system	Structured criteria (28 rules)	Depends on submitter evidence
Clinical use	Primary method for reporting	Supporting reference

In short:

• ACMG = How to interpret a variant

• ClinVar = Where previous interpretations are stored

Limitations of ClinVar as a Primary Interpretation Source

While ClinVar is extremely valuable, relying solely on it for variant classification has several limitations.

1. Conflicting interpretations - Different laboratories may submit different classifications for the same variant. Studies have shown that interpretation discrepancies between labs are relatively common.

2. Variable evidence quality - Not all ClinVar submissions include the same level of supporting evidence.

3. Potentially outdated information - Variant classifications can change over time as new evidence emerges.

4. Laboratory responsibility - Clinical laboratories remain responsible for their own interpretation and cannot rely solely on external databases.

How ClinVar Should Be Used in Germline Testing

ClinVar is best used as supporting evidence within the ACMG framework, not as the primary interpretation system.

For example, ClinVar can contribute evidence such as:

• Previously reported pathogenic variants

• Variant frequency across clinical submissions

• Published literature references

• Expert panel consensus

These data can then be incorporated into ACMG evidence categories such as PS1, PM5, or PP5 when appropriate.

The Emerging Role of ClinGen

In recent years, the Clinical Genome Resource (ClinGen) has further refined variant interpretation standards.

ClinGen expert panels review specific genes and diseases and apply ACMG-based criteria with gene-specific refinements, improving consistency and clinical accuracy.

ClinGen-curated variants are often deposited into ClinVar to make them accessible to the global community.

Recommended Best Practice for Germline Genetic Testing

Most international clinical laboratories follow a three-layer interpretation framework:

1. Primary interpretation framework

ACMG/AMP variant interpretation guidelines

2. Supporting knowledge bases

• ClinVar

• ClinGen

• HGMD

• gnomAD

• OMIM

3. Internal clinical interpretation

• Laboratory curation

• Bioinformatics pipelines

• Literature review

• Clinical correlation

What Should a High-Quality Germline Testing Laboratory Have?

When evaluating the reliability of a genetic test, it is important to consider more than just the sequencing technology.

A high-quality germline testing laboratory should include:

• ACMG-based variant interpretation

• Robust bioinformatics pipelines

• Curated variant databases

• Expert geneticists and molecular pathologists

• International EQA participation

• Clinical laboratory accreditation (ISO15189 or CAP)

These elements ensure that variant classifications are scientifically sound and clinically meaningful.

Conclusion

ClinVar and ACMG guidelines are often misunderstood as competing systems, but in reality they serve complementary roles.

• ACMG guidelines provide the international standard for variant interpretation and clinical reporting.

• ClinVar serves as a valuable global database that supports evidence gathering and data sharing.

For germline genetic testing, the internationally recommended approach is to use ACMG-AMP guidelines as the primary interpretation framework while referencing ClinVar as a supporting knowledge resource.

This integrated approach ensures that variant classifications remain consistent, transparent, and clinically reliable, ultimately improving the quality of genomic medicine.