| Mild ID (IQ 50-70) | Individuals may have delayed language and learning difficulties but can achieve independence in daily living with support |
| Moderate ID (IQ 35-50) | Requires more support for academic, vocational, and daily living skills |
| Severe ID (IQ 20-35) | Significant support needs for all daily activities |
| Profound ID (IQ <20) | Continuous support required for all aspects of life |
| Epilepsy | Occurs in 15-30% of individuals with ID, with certain genetic etiologies having particularly high epilepsy risk |
| Autism spectrum disorder | Approximately 30-40% of individuals with ID meet criteria for ASD |
| Cerebral palsy | Common in individuals with ID due to shared prenatal/perinatal risk factors |
| Sensory impairments | Vision and hearing deficits are more common |
| Fragile X syndrome (FXS) | Caused by CGG repeat expansion in the FMR1 gene, leading to transcriptional silencing. FXS is the most common inherited cause of ID and the leading single-gene cause of autism. |
| Synaptic scaffolding | SHANK2, SHANK3, DLGAP1, DLGAP2 |
| Synaptic receptors | GRIN2A, GRIN2B (NMDA receptor subunits) |
| Presynaptic proteins | SYNGAP1, STXBP1, MUNC18-1 |
| Databases | OMIMOrphanetClinicalTrialsPubMed |