Vertex Pharmaceuticals said late Thursday that another attempt to treat the liver disease known as Alpha-1 Antitrypsin Deficiency has fallen short, and shares tumbled 13.8% in premarket trading on Friday.

The company disclosed results of a Phase 2 drug trial that had been seen as a shot at redemption for the stock, which fell more than 20% in October when another treatment failed in the same disease.

Analysts, however, remained positive on the stock late Thursday. Many argued that the stock remains undervalued based on the company's cystic fibrosis business alone.

"While acknowledging short term headwind, we think the valuation creates an attractive entry point," wrote Citi analyst Mohit Bansal in a note out late Thursday. Bansal says that he values the cystic fibrosis business, without any of the company's pipeline assets, at $225 per share, well above the $190 per share range it was trading after the announcement.

In March, Barron's argued that the selloff in Vertex shares was overdone , and that its cystic fibrosis drugs remain a powerhouse with a long patent life ahead of them. That thesis still holds up, though the stock is sure to tumble in the near term.

Vertex (ticker: VRTX) said Thursday that the AATD drug, called VX-864, increased levels of functional alfa-1 antitrypsin, the protein missing in patients suffering from the disease, but likely not enough to provide clinical benefit. The company said it would stop developing the drug, but said that the trial had provided a proof of concept, and that it would try again with a new compound.

"With these results, we're one step closer to reaching our goal of developing small molecule correctors to treat the underlying cause of AATD, and we're committed to doing so," said the company's CEO, Dr. Reshma Kewalramani, on an investor call late Thursday.

As Barron's wrote in March, AATD is a substantial market, and analysts had thought VX-864 could bring more than $5 billion in revenue a year by 2030. While Vertex's cystic fibrosis business is healthy and expanding, with the company receiving approval for its drug Trikafta in children aged six to 11 earlier this week , investors have grown concerned about its lineup of products in development.

The failure announced Thursday will disappoint investors focused on the pipeline, but analysts say the stock remains sharply undervalued.

"Short-term investors 'perceive' a miss here and a data vacuum in near term," Jefferies analyst Michael Yee wrote on Thursday. "But longer-term investors should find lots of value at $185-190 and trading below its [cystic fibrosis] base value of $200-225 implying all the pipeline such as sickle-cell disease is all free now."

Cowen analyst Phil Nadeau also wrote that investors are giving little value to the pipeline, though he noted that little development-related news remains on the calendar for this year, so it's unclear what could bring investors back.

Speculation that Vertex may seek to make acquisitions swirled earlier this year, though Kewalramani batted it back in an interview with Barron's at the time. Now, SVB Leerink analyst Geoffrey Porges says that the company may feel pressured to pick something up. "With Vertex's pipeline this sparse, we expect the company to be forced to contemplate larger research-driven transactions to bolster their limited development pipeline," he wrote Thursday.

Meanwhile, early Friday, Vertex offered a reminder of why the company remains an analyst darling, with an update on a small study of the gene-editing therapy it is developing with CRISPR Therapeutics (CRSP). The therapy, known as CTX001, is being tested in patients with transfusion-dependent beta thalassemia and severe sickle cell disease.

The data Friday came from 22 patients with more than three months of follow-up after receiving their treatment, and the company said that the patients had shown a consistent and sustained response. The 15 patients with beta thalassemia were transfusion independent after the treatment. Five of those patients have a follow-up of greater than one year.

"These results add to the growing body of evidence that CTX001 may hold the promise for a one-time functional cure for sickle cell disease and beta thalassemia," Kewalramani said in a statement.

In a note out early Friday, SVB Leerink's Porges said that the gene-editing good news wouldn't stop the stock from trading down sharply Friday.

Vertex shares were down 8.3% so far this year as of the market's close on Thursday, and down 19.3% over the past 12 months.