There are prenatal, perinatal, and postnatal causes of ID. Some prenatal causes (e.g., environmental influences) are preventable. Genetic causes account for 45% of ID (Batshaw, Roizen, & Lotrecchiano, 2013). Down syndrome is the largest genetic cause of ID, and Fragile X syndrome is the largest inherited cause of ID. Fetal alcohol syndrome is the largest environmental cause of ID.
- Genetic syndromes (e.g., Down syndrome and Fragile X syndrome)
- Inborn errors of metabolism
- Brain malformation (e.g., microcephaly)
- Maternal disease (e.g., placental disease)
- Environmental influences (e.g., alcohol, other drugs, toxins, teratogens)
- Labor and delivery–related events (leading to neonatal encephalopathy)
- Anoxia at birth
- Hypoxic ischemic injury
- Traumatic brain injury
- Demyelinating disorders
- Seizure disorders (e.g., infantile spasms)
- Severe and chronic social deprivation
- Toxic metabolic syndromes and intoxications (e.g., lead, mercury)
Cross-cultural attitudes and beliefs may influence some individuals perceptions about ID and its causes (Allison & Strydom, 2009; Scior, 2011).