Electrophysiological Phenotype in Angelman Syndrome Differs Between Genotypes

Abstract

Background: Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by either disruptions of the gene UBE3A or deletion of chromosome 15 at 15q11-q13, which encompasses UBE3A and several other genes, including GABRB3, GABRA5, GABRG3, encoding gamma-aminobutyric acid type A receptor subunits (β3, α5, γ3). Individuals with deletions are generally more impaired than those with other genotypes, but the underlying pathophysiology remains largely unknown. Here, we used electroencephalography (EEG) to test the hypothesis that genes other than UBE3A located on 15q11-q13 cause differences in pathophysiology between AS genotypes.

Methods: We compared spectral power of clinical EEG recordings from children (1-18 years of age) with a deletion genotype (n = 37) or a nondeletion genotype (n = 21) and typically developing children without Angelman syndrome (n = 48).

Results: We found elevated theta power (peak frequency: 5.3 Hz) and diminished beta power (peak frequency: 23 Hz) in the deletion genotype compared with the nondeletion genotype as well as excess broadband EEG power (1-32 Hz) peaking in the delta frequency range (peak frequency: 2.8 Hz), shared by both genotypes but stronger for the deletion genotype at younger ages.

Conclusions: Our results provide strong evidence for the contribution of non-UBE3A neuronal pathophysiology in deletion AS and suggest that hemizygosity of the GABRB3-GABRA5-GABRG3 gene cluster causes abnormal theta and beta EEG oscillations that may underlie the more severe clinical phenotype. Our work improves the understanding of AS pathophysiology and has direct implications for the development of AS treatments and biomarkers.

Trial registration: ClinicalTrials.gov NCT00296764.

Keywords: Angelman syndrome; Biomarkers; EEG; GABA; GABRB3-GABRA5-GABRG3 gene cluster; UBE3A.

Conflict of interest statement

Disclosures

Pilar Garces, Maria-Clemencia Hernandez, Joerg F. Hipp, Marius Hoener, Omar Khwaja, Michelle Krishnan and Meghan Miller are full-time employees of F. Hoffmann-La Roche Ltd.; Joel Frohlich is a former employee of F. Hoffmann-La Roche Ltd. (until July 2017); Shafali Jeste, Benjamin Philpot, and Alexander Rotenberg serve as a consultants for and have received funding from F. Hoffmann-La Roche Ltd.. All other authors report no biomedical financial interests or potential conflicts of interest.

Copyright © 2019 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1.. Schematic of 15q11-q13.

The maternally expressed (i.e., paternally imprinted in neurons) gene UBE3A is shown in red, paternally expressed (i.e., maternally imprinted in neurons) genes are shown in blue. Genes shown in black are non-imprinted (i.e., biallelically expressed); “n“ indicates the number of participants for different genotypes. UBE3A mutations (n = 10), paternal UPD (n = 4), imprinting defects (n = 5; could either be deletion within the imprinting center or an abnormal epigenetic imprint), and abnormal DNA methylation that are not deletions (could be either UPD or imprinting defects, n = 2) primarily affect UBE3A. These etiologies comprise the non-deletion genotype (n = 21) in our study. Note that UPD features additionally biallelic expression of paternally imprinted genes (blue). Deletions of 15q11-q13 are typically between canonical break point (BPs) as indicated in the figure. Class I is a ~6 Mb deletion from BP 1 to BP3 (n = 10) that includes four additional genes near the centromere as compared with class II (~5 Mb) deletions, which span BP2 to BP3 (n = 24). Together with atypical (n = 2) and unknown (n = 1) deletion classes, class I and class II deletions comprise the deletion genotype (n = 37) examined in our study. Both deletion classes encompass the GABAAR β3-α5-γ3 subunit gene cluster (i.e., GABRB3, GABRA5, and GABRG3), which is central to the interpretation of our results.

Figure 2.. Spectral power differences between AS and TD controls.

(A) Grand average power spectral density derived from the LMM, with age set to the mean log age of 5.4 years (average across all visits and electrodes). AS: red, TD controls: black. The colored bands show 95% confidence intervals. (B,C) Scalp topography of power change in dB and effect size (Cohen’s d) between AS and TD controls derived from the LMM for 2.8 Hz (i.e., AS delta peak frequency) and the mean log age of 5.4 years. (D) Developmental trajectory of channel averaged delta power (2.8 Hz) derived from the LMM. Longitudinal visits are connected by solid lines.

Figure 3.. Spectral power in delta frequency band differs between AS genotypes.

(A) Developmental trajectory of electrode averaged delta power (2.8 Hz) derived from the LMM (average across all electrodes). Deletion AS: green, Non-deletion AS: blue. Longitudinal visits are connected by solid lines. (B,C) Scalp topography of power change in dB and p-values for t-tests between deletion AS and non-deletion AS derived from the LMM for 2.8 Hz and the mean log age of 4.7 years.

Figure 4.. Spectral power in beta frequency band differs between AS genotypes.

(A) Developmental trajectory of electrode averaged beta power (23 Hz according to hypothesis 2, i.e. peak frequency derived from Dup15q syndrome EEG phenotype, (35)) derived from the LMM (average across all electrodes). Deletion AS: green, Non-deletion AS: blue. Longitudinal visits are connected by solid lines. (B,C) Scalp topography of power change in dB and p-values for t-tests between deletion AS and non-deletion AS derived from the LMM for 23 Hz and the mean log age of 4.7 years

Figure 5.. Spectral power differs between AS genotypes.

(A) Grand average power spectral density derived from the LMM with age set to the mean log age of 4.7 years (average across all visits and electrodes). Deletion AS: green, non-deletion AS: blue. The colored bands show 95% confidence intervals. The black bar indicates frequency ranges with significant group differences (corrected for multiple testing across frequencies). The gray lines indicate the specific hypotheses tested in the delta and beta bands (see Figures 3 and 4). (B) Difference in spectral power between deletion AS and non-deletion AS. The colored bands show 95% confidence intervals. (C) Developmental trajectory of theta power (5.3 Hz) derived from the LMM (average across all electrodes). Longitudinal visits are connected by solid lines. (D) Correlation between theta peak frequency and age. Longitudinal visits are connected by solid lines. (E-G) Scalp topography of power change in dB, effect size (Cohen’s d) and p-values for t-tests between deletion AS and non-deletion AS derived from the LMM for 5.3 Hz and the mean log age of 4.7 years.