A family living in the isolated Appalachian Mountain region of eastern Kentucky has been intermarrying and inbreeding for so many generations that the genetic damage is actually starting to turn their skin blue.
Inbreeding can cause a genetic anomaly known as gene recombination. Recombination increases the likelihood that undesirable recessive genes will meet and end up being expressed to the detriment of the person bearing them. This phenomenon is the medical reason behind cultural taboos against incest.
The recombination of recessive genes in this instance has created an increased incidence of a rare blood condition that makes peoples' skin appear blue.
The "Blue Family" originally settled along the banks of Kentucky's Troublesome Creek, according to The Daily Mail, laying claim to the property by virtue of a 19th century land grant. The whole line traces their genealogy back to a single, French orphan named Martin Fugate. Martin wed a red-haired American bride with a very pale complexion.
By sheer luck, their children inherited the rare mutation that turned their skin blue.
The condition is called methaemoglobinaemia (met-H for short). Persons suffering from met-H create defective hemoglobin which reduces the ability of their red blood cells to carry oxygen throughout their bodies. Because oxygentated blood is lighter in color, the diminshed blood-oxygen levels in people with met-H causes their skin to take on a bluish hue.
Martin Fugate's children may have inherited the met-H gene by accident, but the rampant intermarriage that took place in subsequent generations solidified the mutation's place in the family's gene pool.