FILE PHOTO: Signage for GlaxoSmithKline is seen on its offices in London, Britain, March 30, 2016. REUTERS/Toby Melville/File Photo

LONDON (Reuters) - GlaxoSmithKline is swimming against the tide by getting out of treatments for rare diseases at a time when rivals like Sanofi and Shire see the field as a rich seam for profits.

Successful medicines for rare conditions are potentially very lucrative, since prices frequently run into hundreds of thousands of dollars, but patient numbers can be extremely low.

New GSK Chief Executive Emma Walmsley announced the strategic review and potential divestment of rare diseases on Wednesday as part of a wide-ranging drive to streamline pharmaceutical operations.

It follows a less than impressive experience for GSK in the field, including the fact that its pioneering gene therapy Strimvelis only secured its first commercial patient in March, 10 months after it was approved for sale in Europe in May 2016.

Since then a second patient has also been treated and two more are lined up to receive the therapy commercially, a spokesman said.

Strimvelis, which GSK developed with Italian scientists, is designed for a tiny number of children with ADA Severe Combined Immune Deficiency (ADA-SCID). SCID is sometimes known as “bubble baby” disease, since those born with it have immune systems so weak they must live in germ-free environments.

The new treatment became the first life-saving gene therapy for children when it was approved last year, marking a step forward for the emerging technology to fix faulty genes.

Walmsley said GSK was not giving up on gene and cell therapy entirely. Research will be focused in future in areas with larger potential patient numbers, including oncology.