May 14 (Reuters) - The U.S. Food & Drug Administration

has extended its review of Ascendis Pharma's ( ASND ) therapy to

treat adult patients with a hormone disorder by three months,

the company said on Tuesday.

U.S.-listed shares of the company were down 6.6% in late

afternoon trading.

The health regulator notified that data submitted for the

ongoing review of the therapy, called TransCon PTH, constituted

"a major amendment" to the company's application seeking market

approval.

Last year, the FDA declined to approve the Danish

drugmaker's once-daily therapy, TransCon PTH, citing concerns

linked to manufacturing controls of the drug and device

combination.

The FDA, however, did not express any concerns about the

clinical data submitted at that time and did not seek fresh

pre-clinical or late-stage trials in its so-called complete

response letter.

The FDA is now set to make its decision known by Aug. 14.

Ascendis CEO Jan Mikkelsen said the company has responded to

all requests received to date from the FDA and will work with

the agency as it continues its review.

The disorder known as hypoparathyroidism is caused by the

absence of the parathyroid hormone that regulates calcium and

phosphorus levels in the body.

The disorder causes low calcium levels and high

phosphorus levels in the blood, in which patients suffer from

muscle cramps, seizures and long-term symptoms such as high risk

of kidney disease and depression.

The current standard-of-care treatment for the condition is

the daily intake of vitamin D and calcium supplements.

Tokyo-listed drugmaker Takeda's Natpara was the

only approved treatment for this condition, but unresolved

supply issues have resulted in discontinuation of the treatment.

Ascendis' therapy, marketed under the name Yorvipath,

gained approval in UK in April. It is already available in

Germany and Austria and had first-quarter sales of 1.5 million

euros ($1.62 million) for the first two months since its launch.

($1 = 0.9244 euros)