Deep in the mountains of eastern Kentucky, a family became famous for an extraordinary physical characteristic.

Some members of the Fugate family had skin that appeared distinctly blue or bluish-purple.

The story traces back to Martin Fugate, who settled in the Troublesome Creek region in the early 19th century. He married Elizabeth Smith, and several of their descendants inherited an unusual blood disorder.

The condition was methemoglobinemia, a disorder in which too much hemoglobin becomes oxidized into methemoglobin. Unlike normal hemoglobin, methemoglobin has difficulty delivering oxygen to tissues.

The result can be striking.

Because the blood becomes unusually dark, people with the condition can develop a blue or slate-colored appearance, particularly noticeable in lighter skin.

The Fugate family’s geographic isolation helped the trait persist. Families living in remote Appalachian communities sometimes married within a relatively small local population, increasing the likelihood that relatives carrying the same rare genetic variant would have children who inherited the condition.

For generations, the unusual blue coloration remained poorly understood.

Then, in the 1960s, hematologist Madison Cawein investigated members of the family and identified the underlying problem.

There was an unexpectedly simple treatment.

Methylene blue could help convert methemoglobin back into functional hemoglobin, causing the characteristic blue coloration to disappear as the blood chemistry normalized.

The Fugates became one of the most famous examples of a rare inherited blood disorder in American medical history.