Startle epilepsy is a rare neurologic disease characterized by frequent and spontaneous epileptic seizures (frequently with symmetrical or asymmetrical tonic features) triggered by a normal startle in response to a sudden and unexpected somatosensory (most frequently auditory) stimulus. Falls are common and can be traumatic. In most cases, the disease is associated with spastic hemi-, di-, or tetraplegia and intellectual disability.

Subnormal intellectual functioning which originates during the developmental period. Intellectual disability, previously referred to as mental retardation, has been defined as an IQ score below 70.