Why it's not good to keep it in the 'family'

Polygamy is one of the dark not-so secrets of Mormon Church history. Until about 100 years ago, it was common practice. In fact, presidential contender Mitt Romney is the great-great grandson of a venerated polygamist martyr.

Only its fundamentalist break-away sect, lead by previously most-wanted Warren Jeffs, still practices polygamy, which has caused them plenty of problems, including health, according to ABC News.

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.

The group, who wear conservative 19th-century clothing, is led by Warren Jeffs, who was arrested in August and charged as an accomplice to rape for using his authority to order a 14-year-old girl against her wishes to marry and have sex with her 19-year-old cousin.