AstraZeneca PLC and Merck & Co. Inc. said the U.S. Food and Drug Administration granted orphan drug designation to selumetinib for treating neurofibromatosis type 1, a genetic disorder.

Neurofibromatosis type 1, or NF1, is caused by a gene mutation and causes soft skin lumps, skin pigmentation and nervous system tumors. The incurable disease may also cause pain, motor dysfunction, disfigurement, learning difficulties, visual impairment, high blood pressure and epilepsy, among other complications.

Selumetinib works by blocking the MEK enzyme, potentially stopping a tumor's growth. The potential benefit of the therapy in NF1 is being studied in a phase 1/2 trial, and phase 2 results are expected later in 2018.

The FDA grants orphan drug designation to therapies for rare diseases that affect fewer than 200,000 people in the country. NF1 affects one in 3,000 births.

Selumetinib is also being investigated in a phase 3 trial in certain patients with thyroid cancer. In 2016, the therapy was granted FDA orphan drug designation for the adjuvant treatment, in which it is applied after initial treatment, of differentiated thyroid cancer.

AstraZeneca licensed selumetinib from Boulder, Colo.-based Array BioPharma Inc. in 2003.

On Feb. 1, Array BioPharma sought at least $192 million from AstraZeneca PLC for an alleged breach of their licensing agreement.