The prevalence of seizures in DS appears to peak in infancy and late in life.
Seizures occur in 5–10% of children with DS [Pueschel et al., 1991; Stafstrom et al., 1991; McVicker et al., 1994]. Different seizure types are reported, including infantile spasms, tonic–clonic, myoclonic, and generalized seizures. In our population, seizures occur in 50% (9/18) of middle-aged and 55% (11/20) of elderly DS adults.
Three have a history of onset of seizures in childhood, one of whom is reported to have had infantile spasms. All others have onset of seizures in adulthood. Seizures can be associated with the onset and progression of Alzheimer-type changes in the brain [Stafstrom et al., 1991], being largely responsible for the increase in epilepsy among elderly patients with DS. The literature states that “almost all” DS adults 40 years and older have evidence of declining abilities and evidence of Alzheimer disease changes on magnetic resonance imaging (MRI), EEG, and neuropathological examination of the brain.
Clinical dementia stemming from Alzheimer disease appears later in the coure of the illness. In a study of 53 individuals with DS living in institutions [Lai and Williams, 1989], dementia was found to be present in 8% (2/25) of patients 35–49 years old, 55% (11/20) of patients between 50 and 59 years old, and 75% (6/8) of those patients over 60 years old. Eighty-four percent of the reported demented patients have seizures, and 20% have symptoms of Parkinson disease.
DS men are three times more likely to develop Alzheimer disease symptoms compared with DS women [Schupf et al., 1998]. DS adults with apolipoprotein E3/4 and 4/4 genotypes are four times more likely to develop Alzheimer disease symptoms compared to those with the 3/3 genotype [Schupf et al., 1998].