MBOAT7 encephalopathy: Characterizing the neurology and epileptology

Abstract

Objective: Biallelic pathogenic MBOAT7 variants are associated with neurodevelopmental disorders, intellectual disability (ID), epilepsy, and neuropsychiatric disorders such as attention-deficit/hyperactivity disorder and autism spectrum disorders. We aimed to characterize the epilepsy phenotype in a cohort of patients affected by this syndrome.

Methods: We describe epilepsy features, electroencephalography, magnetic resonance imaging (MRI) findings, antiseizure treatment response, and neurodevelopment of 15 patients with biallelic MBOAT7 variants.

Results: All 15 patients had ID or developmental delay (DD). Twelve suffered from epilepsy, with mean age at seizure onset of 36 months (range = 2 months-6.5 years) and 10 of 12 showing signs of DD before seizure onset. Patients with epilepsy presented with focal motor seizures with impaired awareness (n = 3), focal tonic-clonic seizures and epileptic spasms (n = 1), focal to bilateral tonic-clonic seizures (n = 1), unknown onset bilateral tonic-clonic seizures (n = 2), myoclonic seizures (n = 4), myoclonic-atonic seizures (n = 1), atonic seizures (n = 1), tonic seizures (n = 1), and myoclonic absences (n = 2). Seizure freedom was achieved in 66.7% (8/12), with variable antiseizure treatment regimes. We reviewed electroencephalograms of the patients with epilepsy. Background activity was normal in 64%, whereas 36% had either a generalized or a focal slowing. Interictal epileptiform discharges (IEDs) were reported in 83%. Generalized spikes/polyspikes were found in 53%, multifocal IEDs in 23%, and parasagittal focal IEDs in 26%. The most frequent abnormal brain MRI findings, reported in 58% of patients, included high-intensity signal in T2 and fluid-attenuated inversion recovery (FLAIR) sequences in dentate nuclei and globus pallidus. Biallelic missense variants seemed to be associated with better cognitive and motor outcomes compared to truncating variants and in-frame deletions.

Significance: Biallelic MBOAT7 variants are associated with global developmental impairment in all affected patients and epilepsy in the majority. The seizure semiology is heterogenous. One third of our cohort had persistent seizures despite treatment. The most frequent MRI findings were hyperintensities in T2/FLAIR sequences in dentate nuclei and globus pallidus.

Keywords: electroencephalography; epilepsy; genetics; lysophosphatidylinositol acyltransferase 1; neurodevelopmental disorder.

FIGURE 1

Schematic representation of the localization of variants within MBOAT7 in both the present cohort and population and clinical databases (Genome Aggregation Database [gnomAD] and ClinVar), along with zygosity for the patients in our cohort and functional consequence.

FIGURE 2

Interictal electroencephalogram from Patient 5 in our cohort, aged 10 years 2 months, showing interictal epileptiform discharges with right central (A), midline (B), and anteriorly predominant diffuse (C, D) distributions.

FIGURE 3

T2‐weighted magnetic resonance imaging from Patient 5 in our cohort, showing the most frequently reported finding of high‐intensity signal at dentate nuclei (A) and globus pallidus (B), highlighted by arrows, as well as a mild hyperintensity and asymmetry of the left mesial temporal lobe (B), possibly indicative of a malformation of cortical development such as a focal cortical dysplasia.