The Pope is trying to end the stigma of people afflicted with Huntington's Disease.
Francis held an audience at the Vatican with Huntington's sufferers and their families, as well as patient organisations and researchers trying to find treatments and a cure.
The incurable genetic disorder affects the brain, and has a range of symptoms including serious involuntary movements and psychiatric problems. Many sufferers are left shunned and isolated in their communities.
Organisers said Francis is the first world leader to recognise the plight of those with Huntington's, and said the audience marked the start of a global awareness campaign.
Many of the families came from South America, where Huntington's is 1,000 times more prevalent than in the rest of the world.
It is particularly prevalent in Venezuela, where the affected gene was first identified 25 years ago.