March 18 (Reuters) - The U.S. health regulator on Monday

approved UK-based Orchard Therapeutics' gene therapy to treat

children with metachromatic leukodystrophy (MLD), making it the

first approved treatment in the United States for the rare,

hereditary disease.

Orchard, which was acquired by Japanese pharmaceutical firm

Kyowa Kirin ( KYKOF ) for $477.6 million last year, said it will

provide details on the pricing and availability of the therapy

later in the week.

The one-time therapy, branded as Lenmeldy in the U.S., is

approved for children in certain stages of disease progression,

the Food and Drug Administration (FDA) said.

The approval was based on data from 37 children who received

Lenmeldy in two open-label clinical trials, whose results showed

that the therapy significantly reduced the risk of severe motor

impairment or death compared with untreated children.

The regulator also flagged potential risk of blood cancer

associated with the treatment, along with formation of blood

clots or a type of swelling of brain tissues.

MLD, which affects the brain and nervous system, is

characterized by the buildup of certain fatty substances in the

cells, and leads to loss of motor and cognitive function and

early death.

The disease is estimated to affect one in every 40,000

individuals in the United States, according to the FDA.

Before Orchard was acquired, TD Cowen analyst Yaron Werber

had estimated peak sales of $300 million globally for the

therapy, with annual sales of less than $70 million till 2025.

The brokerage no longer covers Orchard.

The therapy is approved in the European Union and sold under

the brand name Libmeldy.

(Reporting by Mariam Sunny in Bengaluru; Editing by Sriraj

Kalluvila and Devika Syamnath)