Adds background in paragraphs 4-6 and 12, details on drug in paragraph 7,10, company executive comment in paragraph 8

Feb 11 (Reuters) - The U.S. Food and Drug Administration said on Tuesday it has approved SpringWorks Therapeutics' SWTX.O drug to treat a type of rare genetic disorder, which causes tumors to grow in the tissue that covers nerves throughout the body.

Shares of the company were up 4% in extended trading.

The oral drug, branded as Gomekli, was approved for adults and children 2 years of age and older suffering from the condition known as neurofibromatosis type 1 (NF1), with symptomatic plexiform neurofibromas in which the tumor cannot be surgically removed.

In 2020, the health regulator had approved AstraZeneca's AZN.L Koselugo for children with NF1-PN, making it the first specific drug to get the green light.

SpringWorks estimates that around 100,000 patients are living with NF1 in the U.S., of which 30%-50% are likely to develop plexiform neurofibromas.

Patients with NF1 have an eight to 15-year mean reduction in their life expectancy compared to the general population.

SpringWorks' Gomekli belongs to a class of drugs known as MEK inhibitor and is designed to inhibit protein types MEK1 and MEK2.

"In addition to a capsule, we offer a tablet that dissolves in water, which is really important for patients unable to swallow, and those who couldn't previously receive therapy," CEO Saqib Islam had told Reuters ahead of the FDA decision.

The approval was based on a mid-stage trial, where the drug showed 20% or more reduction in tumor volume in 52% of pediatric and 41% of adult patients.

Gomekli is expected to be available in the U.S. within two weeks, the company said.

Earlier this week, Germany's Merck KGaA MRCG.DE said it was in advanced talks to acquire SpringWorks.

Gomekli is SpringWorks' second drug to receive the FDA's nod after Ogsiveo, which is approved for desmoid tumors — abnormal growth that occurs in connective tissues and is associated with a high rate of recurrence.

(Reporting by Christy Santhosh, Kamal Choudhury and Sriparna Roy in Bengaluru; Editing by Mohammed Safi Shamsi and Shilpi Majumdar)

((Christy.Santhosh@thomsonreuters.com))