Precision therapy for a new disorder of AMPA receptor recycling due to mutations in ATAD1

Abstract

Objective: ATAD1 encodes Thorase, a mediator of α-amino-3-hydroxy-5-methylisoxazole-4-proprionate (AMPA) receptor recycling; in this work, we characterized the phenotype resulting from ATAD1 mutations and developed a targeted therapy in both mice and humans.

Methods: Using exome sequencing, we identified a novel ATAD1 mutation (p.E276X) as the etiology of a devastating neurologic disorder characterized by hypertonia, seizures, and death in a consanguineous family. We postulated that pathogenesis was a result of excessive AMPA receptor activity and designed a targeted therapeutic approach using perampanel, an AMPA-receptor antagonist.

Results: Perampanel therapy in ATAD1 knockout mice reversed behavioral defects, normalized brain MRI abnormalities, prevented seizures, and prolonged survival. The ATAD1 patients treated with perampanel showed improvement in hypertonicity and resolution of seizures.

Conclusions: This work demonstrates that identification of novel monogenic neurologic disorders and observation of response to targeted therapeutics can provide important insights into human nervous system functioning.

Figure 1. Subjects' pedigree demonstrates multiple affected individuals in a highly consanguineous family

The proband is patient IV-6; his cousin who was subsequently evaluated and treated is patient IV-3. The ATAD1 variant, p.E276X, was identified by whole-exome sequencing and tracked with disease in all available family members (+ represents the normal allele and − represents the p.E276X allele). See also figure e-1.

Figure 2. Perampanel improves brain MRI differences in ATAD1^−/− mice

(A) Representative ex vivo brain MRIs of wild-type and ATAD1^−/− perampanel-treated and perampanel-untreated mice. (B) Untreated ATAD1^−/− mice (light blue bars) demonstrated volume reduction in all brain areas measured as compared to ATAD1^+/+ mice (black bars). Perampanel therapy (dark blue bars) was associated with a trend toward normalization of brain volumes. (C) Whole-slice T2 MRI signal intensity was significantly increased in ATAD1^−/− mice. This change was reversed with perampanel therapy. (D) T2-signal intensity was increased in ATAD1^−/− mice throughout the brain. Perampanel therapy normalized signal intensity in the striatum and thalamus. For all panels, n = 6. *p = 0.01–0.05, **p = 0.001–0.009, and ***p < 0.001.

Figure 3. Perampanel normalizes behavior and prolongs survival in ATAD1^−/− mice

(A–H) Perampanel, but not phenobarbital, normalized open-field assessments in ATAD1^−/− mice as seen by quantification (A–D) and representative pathview images (E–H) from (A, E) vehicle-treated, ATAD1^+/+, (B, F) vehicle-treated, ATAD1^−/−, (C, G) perampanel-treated, ATAD1^−/−, and (D, H) phenobarbital-treated, ATAD1^−/− mice (n = 6). Open circles represent peripheral activity; closed circles represent central activity. (I and J) On behavioral analysis, ATAD1^−/− mice (red diamonds) cover less distance (L) and rest more (M) than their wild-type littermates (black filled-in circles). Perampanel (blue triangles) reverses the movement deficits, while phenobarbital does not (n = 6). Two mice in the ATAD1^−/− perampanel and phenobarbital-treated groups seized during this observation. The seizures were characterized by high-speed involuntary movements; therefore, they are shown in the figure (symbol surrounded by a black circle), but they are not included in the statistical analysis. (K) Survival is prolonged from 20 days in vehicle-treated ATAD1^−/− mice (red line) to 43 days in ATAD1^−/− perampanel-treated mice (blue line). There is no statistical survival difference between ATAD1^−/− mice treated with vehicle (red line) or phenobarbital (green line). For all panels, *p = 0.01–0.05, **p = 0.001–0.009, and ***p < 0.001. See also figures e-2 and e-3.

Figure 4. Perampanel improves hypertonicity, prevents seizures, and slows neurodegeneration but cannot normalize neurologic function in patients with ATAD1 mutations

(A) Photographs and brain MRIs of the proband, individual IV-6. Initial brain MRI at 2 months showed normal parenchyma, but subsequent studies at 9 and 21 months showed progressive volume loss and hydrocephalus. (B) Photographs and brain MRI of patient IV-3. Brain MRI at 2 months of age was normal. Perampanel was started at 2.5 months of age and follow-up MRI at 9 months of age showed no changes (unlike the progressive neurodegeneration seen in untreated patient IV-6 over the same age range, panel A). (C) Timeline of clinical improvements observed in patient IV-6 and patient IV-4 after the initiation of perampanel therapy. Patient IV-4 also had progression of disease (marked in red) including respiratory failure that was not prevented with perampanel. The bottom panel shows an EEG recorded from subject IV-6 at 15 months of age, prior to therapy with perampanel. (D) Hypsarrhythmia is seen on EEG (gain = 7 μV/mm). (E) The pretreatment recording from panel A is shown at a gain of 30 μV/mm. (F) An example of one of many focal seizures captured on routine EEG prior to perampanel. The lower panel shows the EEG of the same patient 10 weeks after starting perampanel. (G) While on perampanel, the hypsarrhythmia resolved and no focal seizures were noted on follow-up 60-minute routine EEG. This improved EEG pattern was noted on all subsequent follow-up EEGs recorded over a several month period of observation. See also figure e-4.