What happened

Shares of uniQure NV (QURE 2.29%) are plummeting today, down by 40% as of 11:09 a.m. ET. The steep decline came after the company announced interim results from a phase 1/2 clinical study evaluating experimental gene therapy AMT-130 in treating Huntington's disease, a rare neurogenerative disease.

uniQure president of research and development Ricardo Dolmetsch stated that the company was "very pleased" with the interim results. So why did the biotech stock plunge? There were some concerns with the data for AMT-130.

For example, the group of patients treated with the high dose of AMT-130 experienced a 51.5% increase in neurofilament light chain (NfL) protein levels in their cerebrospinal fluid. Higher levels of NfL are viewed as a sign of deteriorating neurodegenerative disease.

Also, uniQure reported that patients in the group receiving the high dose of AMT-130 experienced a 39.7% increase in mutant Huntingtin protein compared to a 4.7% increase in the placebo group. This protein is a driver of Huntington's disease.

So what

Both high and low doses of AMT-130 showed promising patient benefits, including improved motor skills. Both were also generally well tolerated by patients. Investors, though, are focusing heavily on the not-so-great interim results for the high dose of AMT-130.

However, the news was much better with the low dose. Importantly, the low dose didn't appear to have some of the negatives associated with the high dose. Patients receiving the low dose of AMT-130 experienced a 12.9% decline in NfL after two years. They also experienced an 8.1% decrease in mutant Huntingtin protein.

Now what

uniQure plans to add a third cohort to its ongoing U.S. clinical trial in the second half of 2023. It also expects to finish enrolling patients in the high-dose cohort of its European study of AMT-130 in the third quarter of this year. The company hopes to begin meeting with U.S. and European regulators by the first quarter of 2024 about a pathway to advance the development of its experimental gene therapy.