By Jill McGivering
Women are twice as likely as men to develop MS
The number of people suffering from the neurological disease multiple sclerosis (MS) worldwide could be far more than the estimated 1.3m, researchers say.
A major new study into the disease has been launched by the Multiple Sclerosis International Federation (MSIF) and the World Health Organization (WHO).
They hope to answer key questions about MS, the cause of which is unclear.
Governments are being urged to invest more in education and services to improve sufferers' quality of life.
MS is a degenerative disease of the central nervous system. It typically emerges in young adults and can lead to severe disability.
Symptoms often include aching, loss of balance, muscle spasm and paralysis and general fatigue.
But there are still many mysteries surrounding MS.
It is not clear what causes it or why women are twice as likely as men to develop it. Or why it is so much more common in colder countries than warmer ones.
The study has found that although most cases occur in the developed world, every country that took part in the survey, rich or poor, had some instances.
Peer Baneke, the chief executive of the MSIF, says the rough estimate of 1.3m cases worldwide is probably a big underestimation.
"The diagnosis of multiple sclerosis is very difficult," he said. "You really need neurologists who have the knowledge to distinguish it from other things."
It also needs specialist equipment which poorer health systems simply cannot access. MRI scanners, for example, are in short supply in the developing world.
"There must be many people out there who we just don't know about," said Mr Baneke.
The survey also looks at the experiences of people with MS.
In many countries, sufferers face stigma and misunderstanding.
Kanya Puspokusumo, a 36-year-old Indonesian, was diagnosed in 2001.
She said that some people thought MS was similar to Aids. Even though she explained it was not transmitted from one person to another, many still excluded her socially.
Dr Hithaishi Weerakoon is a doctor in Sri Lanka who was diagnosed with MS more than a decade ago.
Many families do not acknowledge MS, she says, and keep affected family members hidden away.
Others say, wrongly, that it has developed as a condition because of sins in a past life.
Those associated with the study say this is an important start - but that far more research needs to be done, especially in developing countries where the process of identifying cases systematically and collecting data is still at a very early stage.