Rationale:
Notched delta is a rare EEG finding that has strongly been associated with Angelman’s disease, a neurodevelopmental disorder with features including developmental delay, speech impairment, and delayed motor skills. It is characterized by a delta wave superimposed by sharp waves or spikes on its descending or ascending phase. This pattern is thought to be due to asynchronous signals reaching the cortex, where spatiotemporal averaging of electrical signals take place.
1 In this report, we describe the case of a patient with Down syndrome with EEG showing notched delta waves.
Methods:
Patient is a 39-year-old woman with history of Down syndrome and epilepsy diagnosed at the age of 29. Her EEG revealed findings consistent with notched delta (Figure 1).
Results:
While the notched delta is considered atypical and has unclear significance, the delta wave is usually associated with diffuse cerebral dysfunction or deep midline structural pathology, and the notches are thought to be caused by epileptiform spikes. It has mostly been reported in Angelman syndrome,
1 with a study describing this finding in 73% of patients with the disease. It has also been described with Rett syndrome, 4p (-) syndrome and Pitt-Rogers-Danks syndrome.
EEGs of patients with Down syndrome and comorbid epilepsy usually reveal epileptiform activity. Apart from this, EEGs in patients with Down syndrome can show diffuse slowing, as well as higher delta and theta activity and lower alpha and beta activity when compared to controls, or slowing of alpha with increase of the power of theta bands after the age of 35, thought to correlate with the development of Alzheimer’s disease.
It has been suggested in previous studies that the notched delta might be secondary to the disruption of the GABA signaling pathway, since Angelman syndrome is caused by the deletion of chromosome 15, which carries GABA-A receptor genes, and Rett syndrome has been associated with reduced expression of GABA receptors. Animal studies have suggested that Down Syndrome is associated with altered GABAergic signaling.
2 Another hypothesis lies in the increased average thickness and decreased thickness variability seen in Down syndrome, indicating abnormal gray matter development in patients with Down syndrome when compared to controls.
3 Conclusions:
While Down syndrome is the one of most common genetic diseases, the number of EEG studies have been limited and are mostly focused on epileptic syndromes associated with the disease or on evidence of premature senile degeneration and diffuse slowing correlating with the development of Alzheimer’s disease. In our report, we describe the finding of notched deltas on EEG in Down syndrome.
Funding: N/A