Pfizer pauses trial for experimental gene therapy drug after child participant dies suddenly

Pfizer has paused its trial of a drug for a rare muscle-wasting disease after a child died suddenly.

The boy, who was between two and four years old, suffered cardiac arrest after receiving the one-off gene therapy last year.

Pfizer has not determined exactly what happened or whether the death was caused by the treatment, called fordadistrogene movaparvovec.

The New York pharma giant said the pause would allow it to investigate the death ‘while protecting the safety of the participants, which is our top priority.’

Pfizer has paused its trial of a drug for a rare muscle-wasting disease after a child died suddenly (stock)

The victim was part of a mid-stage study that enrolled children between the ages of two and four with Duchenne muscular dystrophy.

The rare disease primarily affects boys – about one in 3,500 male births – and patients usually don’t live over the age of 25.

There were three serious adverse events during the study, but all of the children recovered within two weeks. 

Pfizer has paused administering the same gene therapy in a separate final-stage study that enrolled boys aged up to eight.

That study was comparing whether the drug could slow the progression of the disease compared to a placebo.

If the trials went well, it was poised to become one of the most expensive drugs ever. 

A competing gene therapy from Sarepta Therapeutics Inc. won accelerated approval by the FDA last year, becoming the only approved treatment for kids with DMD.

A single dose costs around $3million. 

DMD is caused by a genetic mutation that means the body doesn’t produce enough of a protein called dystrophin, which maintains muscle strength.

Without it, muscles gradually break down, leading to problems walking, sitting and speaking, and eventually affect the muscles around the lungs and heart.

By the age of 11, most sufferers will usually need a wheelchair.

Pfizer’s drug works by introducing a shortened but functional dystrophin protein directly to patients’ muscle cells, slowing their degradation. 

It is administered via a one-time infusion. 

Historically, the only medications used to treat DMD were steroids such as prednisone or deflazacort.

They dampen down inflammation – a major problem in Duchenne – which slows the decline in muscle strength and mobility and can delay heart and lung complications.

But these can cause serious side effects, from weight gain, stunted growth, delayed puberty and a reduction in bone density, which can increase the risk of fractures.