Intellectual disability affects 1 to 3 percent of children worldwide, half of whom are born to parents of normal intelligence. Researchers have discovered that most of these cases of "sporadic intellectual disability" result from new, random mutations arising spontaneously in the children's genes, not from faulty recessive genes inherited from their parents.
The researchers say their finding is one of the first steps in understanding the underlying causes of this condition (also known as mental retardation), which is marked by having an IQ below 70, and is — perhaps surprisingly — the costliest of all health problems. Understanding the cause may eventually lead to new therapies, they said.
Everyone is born with several de novo mutations, or accidental changes in DNA (such as the deletion or duplication of a base pair) not found in one's parents' DNA. Most of the time, these mutations occur in non-crucial parts of DNA and thus cause minimal harm, but sometimes the mutations can have drastic consequences, such as by impairing the function of a gene that influences cognitive development. The new study finds that this random bad luck accounts for the majority of cases of sporadic intellectual disability.
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