UPDATE 1-US FDA approves X4 Pharmaceuticals' therapy for immunodeficiency disease

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April 29 (Reuters) - X4 Pharmaceuticals said on Monday the U.S. FDA has approved its therapy to treat a rare genetic immunodeficiency disease in patients 12 years of age and older, sending its shares up 16% before the bell.

X4's mavorixafor, which will be sold under the brand name Xolremdi, is the first therapy to get U.S. approval specifically for the treatment of WHIM syndrome.

WHIM is characterized by disorders in which the body's immune system does not function properly. It is an acronym for warts, hypogammaglobulinemia or low antibody levels, infections, and myelokathexis or low white blood cell count, which are all symptoms of the disorder.

The decision is based on a late-stage study where the therapy showed 60% reduction in infection rate compared to placebo when tested in patients with WHIM syndrome.

Less than 1,000 people in the United States have WHIM syndrome, according to government data.

(Reporting by Christy Santhosh in Bengaluru; Editing by Shinjini Ganguli and Shilpi Majumdar)