Variant of Uncertain Significance (VUS) in Causation Disputes

Genetic testing is often used in complex medical cases to identify variants that cannot be definitively classified as pathogenic or benign. These findings are commonly referred to as variants of uncertain significance (VUS), and they are more frequently becoming focal points in causation disputes. In litigation, the presence of a VUS does not establish a cause of injury. Reliance on any such findings in court must be supported with evidence that demonstrates clinical relevance, rather than speculation based on uncertainty.

The Nature of a VUS

A VUS reflects a genetic variant for which the available scientific evidence is insufficient to determine its role in disease. It may represent a benign variation within the population or a mutation that has not yet been fully characterized. By definition, it does not carry established diagnostic or prognostic value at the time it is identified.

From a legal perspective, this classification is critical. Courts distinguish between known disease-causing mutations and variants whose significance remains unresolved. A VUS does not, on its own, provide a reliable basis for attributing injury.

The Risk of Overinterpretation

In causation disputes for medical negligence, a variant of uncertain significance may be presented to the court as a potential explanation for neurological or developmental impairment. However, this introduces the risk of overinterpretation, where uncertainty is treated as evidence of causation rather than a limitation of current knowledge.

In court, this may not be acceptable. Arguments need to be grounded in accepted scientific standards. The absence of definitive classification means that conclusions about causation must be approached with caution. Assertions that a VUS explains an injury must be supported by additional evidence demonstrating that the variant is likely to be clinically significant and consistent with the observed condition.

Speculative attribution based on possibility rather than probability does not satisfy evidentiary requirements.

Distinguishing Association From Causation

Even where a genetic variant is associated with a condition, that association does not establish causation in an individual case. This distinction is amplified in the context of a VUS, where the association itself may be unclear or unsupported.

Courts evaluate whether the evidence demonstrates that the variant is capable of producing the specific injury at issue and whether it did so in the patient. This requires analysis of phenotype, clinical course, and consistency with known patterns of disease.

The presence of a VUS does not shift the burden of proof. The party relying on it must demonstrate its relevance through evidence, not inference.

Temporal and Clinical Alignment

A key issue when evaluating a VUS is whether the proposed genetic explanation aligns with the timing and progression of the injury. Many genetic conditions associated with neurological impairment have characteristic developmental trajectories.

Courts examine whether the patient’s clinical course is consistent with such patterns or whether it reflects an acute event inconsistent with genetic disease. Where the timing of injury corresponds to a discrete clinical occurrence—such as a perinatal event—the explanatory value of a VUS may be limited.

The analysis must reconcile the genetic finding with the documented sequence of events.

Plaintiff Emphasizes Established Mechanisms

In response to reliance on a VUS, the plaintiff’s analysis typically focuses on established, evidence-based mechanisms of injury. This includes examination of clinical records, diagnostic findings, and the timing of events to identify a causal pathway supported by known medical principles.

Courts evaluate whether this pathway provides a more reliable explanation than one based on an unresolved genetic finding. The presence of a VUS does not negate causation where the evidence supports that an external event was a substantial factor in producing the injury. Therefore, the inquiry centers on the comparative strength of competing explanations.

Expert Testimony and Methodological Requirements

Expert testimony is pivotal in medical negligence cases. As such, any testimony that addresses a VUS must adhere to rigorous methodological standards set in place by the court. Experts are expected to explain the classification of the variant, the limitations of current knowledge, and the basis for any opinion regarding its significance.

After, the court scrutinizes whether the expert has:

• Distinguished between known and uncertain genetic findings;
• Addressed the absence of definitive evidence regarding pathogenicity; and
• Explained how, if at all, the variant relates to the patient’s condition.

Conclusions that extend beyond the available scientific support may be subject to exclusion or reduced weight.

Evidentiary Constraints and Scientific Development

The classification of genetic variants is subject to ongoing revision as scientific knowledge evolves. A VUS may later be reclassified as benign or pathogenic as additional data becomes available. This dynamic nature further complicates its use in litigation.

Courts consider whether the evidence reflects the current state of knowledge and whether the conclusions drawn are consistent with accepted standards at the time of testimony. Reliance on unsettled or emerging interpretations must be clearly identified as such. The evolving nature of genetic science does not lower the threshold for admissibility or reliability.

Legal Consequences of VUS-Based Arguments

If a VUS is presented as the primary explanation for injury without sufficient supporting evidence, it is unlikely to satisfy the requirements of causation. Courts require a showing that rises above speculation and establishes a probable, not merely possible, cause.

Where a VUS is one of several factors considered, its role is evaluated in the context of the entire evidentiary record. It may be weighed alongside clinical findings, known mechanisms of injury, and other relevant data.

The legal outcome depends on whether the evidence, taken as a whole, supports a coherent and reliable explanation for the injury.

Conclusion

Variants of uncertain significance present a unique challenge in causation disputes, reflecting the limits of current genetic knowledge. Courts require that such findings be interpreted with precision and restraint, recognizing that uncertainty cannot serve as a substitute for proof. The determination of causation depends on whether the evidentiary record supports a defined and reliable explanation for injury, grounded in established science and consistent with the clinical course.

Raynes & Lawn evaluates matters with a focus on cases involving substantial injury, complex causation, and multi-party liability exposure, including those involving advanced genetic evidence and unresolved scientific questions. The firm’s docket reflects a selective intake process, often including referrals from other counsel where the evidentiary and scientific demands exceed the scope of more routine representation. Where a case presents that level of complexity, it is often directed toward firms such as Raynes & Lawn, whose litigation model is structured to address technically intensive and evolving areas of dispute.