One by one, Francis blessed and greeted each of the family members and their caregivers who travelled from around the world for the audience, which organisers said represented the first time a world leader had recognised the plight of those who suffer from Huntington's.
"May none of you ever feel you are alone," Francis told them. "May none of you feel you are a burden. May no one feel the need to run away."
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.
The disease causes cells in parts of the brain to die, resulting over time in involuntary movements, personality and mood changes and slurred speech. Symptoms usually develop between ages 30 and 50. Many suffer from psychiatric problems, including depression and anxiety.
Often the social stigma and superstition associated with Huntington's forces families to keep their relatives hidden isolation that then can be compounded by poverty and discrimination. In some places, suffers are thought to be possessed by the devil.