In a dusty neighborhood under sheer sandstone cliffs studded with juniper on the Arizona-Utah border, a rare genetic disorder is spreading through polygamous families on a wave of inbreeding.
The twin border communities of Hildale, Utah, and Colorado City, Arizona, have the world's highest known prevalence of fumarase deficiency, an enzyme irregularity that causes severe mental retardation brought on by cousin marriage, doctors say.
"Arizona has about half the world's population of known fumarase deficiency patients," said Dr. Theodore Tarby, a pediatric neurologist who has treated many of the children at Arizona clinics under contracts with the state.
"It exists in a certain percentage of the broader population but once you get a tendency to inbreed you're inbreeding people who have the gene there, so you markedly increase the risk of developing the condition," he said.
The community of about 10,000 people, who shun outsiders and are taught to avoid newspapers, television and the Internet, is home to the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS), a sect that broke from the mainstream Mormon church 72 years ago over polygamy.