Which of the following is a genetic cause of intellectual disability?

• A. Abnormal genes
• B. Fetal alcohol spectrum disorders
• C. Infection during pregnancy
• D. Lack of oxygen at birth

Answer: (A)

Genetic factors can underlie intellectual disability because changes in DNA may disrupt brain development or function. Abnormal genes can be inherited or arise spontaneously and can involve whole chromosomes, single-gene mutations, or copy number variations. These genetic alterations are inherent to the individual and can cause cognitive impairment independent of environmental exposures after conception, making abnormal genes the genetic cause.

In contrast, fetal alcohol spectrum disorders come from alcohol exposure during pregnancy, an environmental factor. Infection during pregnancy can cause problems through pathogens affecting fetal development, also environmental. Lack of oxygen at birth is a perinatal injury that damages the brain around the time of birth, not a genetic difference.