Washington: Scientists have linked autism and intellectual disability in newborn males with genetic changes that could result from harmful environmental factors, a study said.
An analysis of 100 million US medical records said that autism and intellectual disability rates are correlated at the county level with incidence of genital malformations in newborn males, an indicator of possible congenital exposure to harmful environmental factors such as pesticides.
Autism rates - after adjustment for gender, ethnic, socioeconomic and geopolitical factors - jump by 283 percent for every one percent increase in frequency of malformations in a county.
The intellectual disability rates increase 94 percent.
Slight increases in autism and intellectual disability rates are also seen in wealthier and more urban counties.
The study, published by scientists from the University of Chicago March 13 in PLOS Computational Biology, confirmed the dramatic effect of diagnostic standards, reported Science Daily.
Incidence rates for autism and intellectual disability on a per-person basis decrease by roughly 99 percent in states with stronger regulations on diagnosis of these disorders.
"Autism appears to be strongly correlated with rate of congenital malformations of the genitals in males across the country," said study author Andrey Rzhetsky, Ph.D, professor of genetic medicine and human genetics at the University of Chicago.
"This gives an indicator of environmental load and the effect is surprisingly strong."
"We interpret the results of this study as a strong environmental signal," Rzhetsky said.
"For future genetic studies we may have to take into account where data were collected, because it's possible that you can get two identical kids in two different counties and one would have autism and the other would not."