The disorder can be inherited, as was the case with the Fugate family, or caused by exposure to certain drugs and chemicals such as anesthetic drugs like benzocaine and xylocaine. The carcinogen benzene and nitrites used as meat additives can also be culprits, as well as certain antibiotics, including dapsone and chloroquine.

The genetic form of methemoglobinemia is caused by one of several genetic defects, according to Tefferi. The Fugates probably had a deficiency in the enzyme called cytochrome-b5 methemoglobin reductase, which is responsible for recessive congenital methemoglobinemia.

“Blue People of Troublesome Creek,” was published in 1982 by the University of Indiana’s Cathy Trost, who described Benjy’s skin as “almost purple.” The Fugate progeny had a genetic condition called methemoglobinemia, which was passed down through a recessive gene and blossomed through intermarriage.

Normally, people have less than about 1 percent of methemoglobin, a type of hemoglobin that is altered by being oxidized so is useless in carrying oxygen in the blood. When those levels rise to greater than 20 percent, heart abnormalities and seizures and even death can occur.

But at levels of between 10 and 20 percent a person can develop blue skin without any other symptoms. Most of blue Fugates never suffered any health effects and lived into their 80s and 90s.