(Reuters) – GlaxoSmithKline’s gene therapy for the so-called “bubble boy” disease was approved by Britain’s healthcare cost watchdog NICE, despite a price tag of almost 600,000 euros ($700,000).

Gene therapy is designed to deliver a one-off cure for the patient and drugmakers are typically asking a hefty price that is comparable to the combined costs of alternative life-long treatment.

Britain’s National Institute for Health and Care Excellence (NICE) said in draft guidance published on Friday that Strimvelis gene therapy used against adenosine deaminase deficiency, or ADA-SCID, improves overall survival compared with standard stem cell transplant therapy.

The inherited condition disables the immune system and without treatment, children with ADA-SCID need to be kept in isolation to avoid infections – hence it has become known as the “bubble baby” or “bubble boy” syndrome.

“Strimvelis represents an important development in the treatment of ADA-SCID, offering the potential to cure the immune aspects of the condition and avoid some of the disadvantages of current treatments,” NICE said.

“Costing 594,000 euros, the treatment is usually given once only and the effects are thought to be life-long,” it added.

The draft guidance marks the first time NICE has applied its new cost effectiveness limits for treatments for very rare conditions.