Shares of Neuralstem Inc. fell 11 percent Friday after the company announced that a clinical hold has been placed on its proposed amyotrophic lateral sclerosis (AML) trial because of concerns raised by the FDA.

Neuralstem, of Rockville, Md., in December filed an investigational new drug application to begin a clinical trial to treat AML patients through spinal injections of its stem cells via its Human Neural Stem Cell technology. That technology involves the isolation of central nervous system stem cells from tissue. Those cells are expanded in vitro up to a billion times and differentiated into human neurons and glia. The process demonstrated promising efficacy in animal models of spinal cord injury and AML.

After an FDA review of the company's IND, the agency "asked for some additional information regarding our product manufacturing process and preclinical studies, as well as our novel clinical delivery injection device and technique," Richard Garr, Neuralstem's president & CEO, said in a statement. He added that the company believes it can provide the information expeditiously.

He also noted that the FDA has requested modifications to the protocol and eligibility criteria for patients in the trial, along with "slight changes" to the timing of the surgeries. He also said the agency had extensive "nonhold" comments, requests for information and recommendations. "These primarily concerned issues that will need to be addressed for final product manufacturing and testing." Garr added.

Shares of Neuralstem (AMEX:CUR) fell 15 cents to close at $1.15.