The future of the Tylenol autism/ADHD lawsuits in federal court will largely depend on the outcome of the upcoming Daubert challenges regarding the admissibility of the each side’s expert witnesses on the issue of causation. If the MDL Judge rules that the plaintiffs’ causation experts should be excluded because their scientific opinions are unreliable, it will mean the end of the Tylenol autism class action MDL.
Defendants Seek to Exclude Plaintiffs’ Experts
Both sides, plaintiffs and defendants, filed their separate objections seeking to exclude the expert testimony of the scientists retained by the other side. This post will summarize the defendants’ Daubert objections for and motions to exclude the opinions of the plaintiffs’ experts. Below is a summary of each of the separate expert witnesses retained by the plaintiffs and a brief summary of their opinions.
Dr. Brandon Pearson
Dr. Brandon Pearson is an Environmental Health Sciences Professor at Columbia University and the lab director of the Columbia Center for Children’s Environmental Health. Dr. Pearson is testifying in this case as the plaintiffs’ expert toxicologist and his opinions are based primarily on preclinical lab studies showing a link between acetaminophen and autism.
Dr. Stan Louie
Plaintiffs’ expert Dr. Stan Louie is a pharmacist and pharmacologist. He is currently a lab director at the University of Southern California. Dr. Louie’s opinions, much like Dr. Pearson’s, are based on animal lab studies from which he proposes two theories of who prenatal use of acetaminophen causes autism and ADHD. The first theory is that use of acetaminophen causes excess NAPQI and oxidative stress. Dr. Louie’s second theory is that acetaminophen causes “epigenetic changes” and DNA changes during gestation.
Dr. Robert Cabrera
Dr. Robert Cabrera is a biologist who specializes in teratology. He is a professor at the Baylor College of Medicine. Dr. Cabrera’s opinions in this case are based on a systematic review of the existing studies and scientific literature. Based on this review, Dr. Cabrera concluded that a causal relationship exists between acetaminophen use during pregnancy and adverse neurodevelopmental outcomes.
Dr. Eric Hollander
Dr. Eric Hollander is a psychiatrist and a Professor in the Department of Psychiatry and Behavioral Sciences at the Albert Einstein College of Medicine. Like the other experts for the plaintiffs, Dr. Hollander also theorizes that acetaminophen exposure during gestation can cause excess NAPQI levels and oxidative stress, resulting in neurodevelopmental issues in the fetus.
Dr. Andrea Baccarelli
Dr. Andrea Baccarelli is one of the plaintiffs’ key expert witnesses in this litigation. Dr. Baccarelli, an epidemiologist, is Chair of the Department of Environmental Health Sciences at Columbia University. He is one of the leading experts in the field and has published over 600 articles.
Most of Dr. Baccarelli’s opinions, in this case, focus on epidemiology, but he does offer his own theories on the mechanisms of how in utero exposure to acetaminophen may cause altered fetal brain development resulting in autism and ADHD. His theories are similar to those of the other experts, focusing on oxidative stress from excess NAPQI levels.
Defense Daubert Arguments for the Exclusion of the General Causation Experts
The defense argues that all of the plaintiffs’ general causation experts (listed above) should be excluded based on Daubert because their opinions do not meet the reliability standards. They set forth several distinct arguments in support of this.
First, the defense claims that the plaintiffs’ experts’ opinions rest on “unreliable leaps of logic.” Specifically, they point out that the biological pathways that lead to autism and ADHD are not fully known, which makes it impossible for the experts to theorize on how acetaminophen could possibly cause these conditions. In other words, if the experts cannot explain how autism or ADHA develop, they cannot theorize that prenatal Tylenol use can trigger that development.
Second, the defense asserts that the plaintiffs’ experts use unreliable scientific methods to analyze and assess the available studies. This is an argument that you see in almost every Daubert challenge. They claim that the experts for the plaintiffs cherry picked which studies to focus on and used unscientific “outcome oriented” methods. They accuse Drs. Baccarelli, Cabrera, Hollander, and Louie of misreading, and twisting the results of various studies to fit their preconceived assumptions.
They also suggest that these same experts fail to account for the limitations of the studies they rely on, and basically ignore other studies indicating that there is no link between Tylenol and autism or ADHD. The defense also attacks the plaintiffs’ experts for their reliance on any prior studies that did not use clinical autism diagnosis as endpoints, claiming that such studies do not provide a reliable basis for general causation opinions.
Finally, the defense contends that the plaintiffs’ experts lack any sort of reliable scientific basis for their theories about the mechanisms by which acetaminophen use during pregnancy leads to autism and ADHD. They claim that the “oxidative stress” theory offered by nearly all of the experts is purely speculative, since the biologic pathways leading to autism are not actually known. In other words, they characterize these theories as “guesses.” As for the other, alternative mechanism theories proposed by some of the various experts, the defense claims that these are based on unreliable methods.
The defense launches a separate attack on the opinions of the plaintiffs’ experts as they relate to the connection between acetaminophen and ADHD. They claim that the plaintiffs’ experts fail to properly account for genetic causes of ADHD when they formed their opinions. The underlying premise of this argument is that ADHD is something that is genetically inherited, and not something caused by exposure to anything during fetal gestation. This will be a central theme of the defense strategy with respect to the ADHD claims moving forward. Unlike autism, there is strong evidence suggesting that genetics play a role in ADHD.