Alnylam Pharmaceuticals, Inc. (Nasdaq: ALNY), a leading RNAi therapeutics company, today announced that it had received a Complete Response Letter (CRL) from the U.S. Food and Drug Administration (FDA) for its supplemental New Drug Application (sNDA) for patisiran for the treatment of the cardiomyopathy of transthyretin-mediated (ATTR) amyloidosis.

Patisiran is an RNA interference (RNAi) therapeutic that silences the gene that produces transthyretin. This protein can misfold and form amyloid fibrils in multiple tissues, including the heart. The FDA has already approved Patisiran for the treatment of the polyneuropathy of hereditary ATTR amyloidosis in adults.

In the CRL, the FDA stated that it did not believe that the data submitted in the sNDA were sufficient to support the approval of patisiran for treating ATTR amyloidosis cardiomyopathy. The FDA specifically cited concerns about the clinical significance of the treatment effect on functional capacity and the safety profile of patisiran in this patient population.

Alnylam said that it is disappointed with the FDA’s decision but remains committed to developing patisiran to treat ATTR amyloidosis cardiomyopathy. The company said it will work with the FDA to address the concerns raised in the CRL and determine the next path forward for the development of patisiran in this indication.

Alnylam has received a CRL from the FDA for its sNDA for patisiran to treat ATTR amyloidosis cardiomyopathy. The FDA cited concerns about the clinical significance of the treatment effect on functional capacity and the safety profile of patisiran in this patient population. Alnylam said that it is disappointed with the decision but remains committed to developing patisiran for this indication.

Alnylam was trying to get approval from the FDA to sell their drug patisiran for a new condition, ATTR amyloidosis cardiomyopathy. The FDA said no because they weren’t sure if the drug was safe or effective for this condition. Alnylam is disappointed, but they’re still going to try to get approval for patisiran for this condition.