Whole Genome Sequence Data From Captive Baboons Implicate RBFOX1 in Epileptic Seizure Risk.

In this study, we investigate the genetic determinants that underlie epilepsy in a captive baboon pedigree and evaluate the potential suitability of this non-human primate model for understanding the genetic etiology of human epilepsy. Archived whole-genome sequence data were analyzed using both a candidate gene approach that targeted variants in baboon homologs of 19 genes (n = 20,881 SNPs) previously implicated in genetic generalized epilepsy (GGE) and a more agnostic approach that examined protein-altering mutations genome-wide as assessed by snpEff (n = 36,169). Measured genotype association tests for baboon cases of epileptic seizure were performed using SOLAR, as well as gene set enrichment analyses (GSEA) and protein-protein interaction (PPI) network construction of top association hits genome-wide (p < 0.01; n = 441 genes). The maximum likelihood estimate of heritability for epileptic seizure in the pedigreed baboon sample is 0.76 (SE = 0.77; p = 0.07). Among candidate genes for GGE, a significant association was detected for an intronic SNP in RBFOX1 (p = 5.92 × 10-6; adjusted p = 0.016). For protein-altering variants, no genome-wide significant results were observed for epilepsy status. However, GSEA revealed significant positive enrichment for genes involved in the extracellular matrix structure (ECM; FDR = 0.0072) and collagen formation (FDR = 0.017), which was reflected in a major PPI network cluster. This preliminary study highlights the potential role of RBFOX1 in the epileptic baboon, a protein involved in transcriptomic regulation of multiple epilepsy candidate genes in humans and itself previously implicated in human epilepsy, both focal and generalized. Moreover, protein-damaging variants from across the genome exhibit a pattern of association that links collagen-containing ECM to epilepsy risk. These findings suggest a shared genetic etiology between baboon and human forms of GGE and lay the foundation for follow-up research.

Mortality in captive baboons with seizures: a new model for SUDEP?

Because the baboon is a model of primary generalized epilepsy, we were interested in mortality of captive animals with a history of witnessed seizures. Causes of natural death were investigated in 46 seizure baboons (SZ) and 78 nonepileptic controls (CTL), all of which underwent a complete pathologic examination at the Southwest Foundation for Biomedical Research (SFBR) in San Antonio. SZ animals died at a younger age than the control baboons (p < 0.001). Almost all epileptic baboons that died suddenly without an apparent cause (SZ-UKN), had pulmonary congestion or edema without evidence of trauma, systemic illness, or heart disease, compared to nine controls (12%) (p < 0.001), most of which demonstrated evidence of a concurrent illness. Serosanguineous bronchial secretions were found in 15 SZ-UKN baboons (58%), but in only three controls (4%) (p < 0.001). Chronic multifocal fibrotic changes in myocardium were noted in only three (12%) of SZ-UKN baboons and one control baboon. Based upon these results, untreated seizures appear to reduce the life expectancy of captive baboons. Sudden unexpected death in epilepsy (SUDEP) may be a common cause of natural death in epileptic baboons.

Craniofacial trauma as a clinical marker of seizures in a baboon colony.

Baboons provide a natural model of epilepsy. However, spontaneous seizures are usually sporadic, brief, and may not be observed. We hypothesized that various types of craniofacial trauma (CFT) may serve as reliable markers for epilepsy. We evaluated the type, demographics, and clinical significance of CFT in a large baboon colony. CFT was categorized according to somatotopic location, propensity to recur, and association with witnessed seizures or abnormal EEG findings. We divided the baboons with CFT into 2 groups: those with known histories of seizures (CFT+Sz, n = 176) and those without seizure histories (CFTonly; n = 515). In CFT+Sz baboons, the 568 injuries identified included periorbital (57%), scalp (27%), muzzle (12%), and facial (4%) injuries; multiple somatotopic locations or body parts were affected in 21 baboons. The most common CFT injuries associated with seizures were periorbital and scalp lesions (43% for each region). Compared with those in CFTonly animals, EEG abnormalities, including interictal epileptic discharges (IED) and photosensitivity were more prevalent in the CFT+Sz group, particularly among baboons with periorbital or scalp injuries. Compared with CFT+Sz animals, CFTonly baboons tended to have later onset and less frequent recurrence of CFT but higher prevalence of muzzle and tooth injuries. IED and photosensitivity were less prevalent in the CFTonly than the CFT+Sz group, with periorbital injuries carrying the highest and muzzle injuries the lowest association with IED or photosensitivity in both groups. Therefore, CFT in general and periorbital injuries in particular may be markers for seizures in baboons.

Electroclinical phenotypes in a pedigreed baboon colony.

This is the first large-scale epidemiological study evaluating the prevalence of interictal epileptic discharges (IEDs) and photosensitivity (PS) recorded by scalp EEG in a natural nonhuman-primate model of photosensitive, generalized epilepsy. Scalp EEG was used to characterize electroclinical phenotypes in a large baboon pedigree housed at the Southwest National Primate Research Center at the Texas Biomedical Research Institute (Texas Biomed) based upon IEDs and photosensitivity. Scalp EEG studies including intermittent light stimulation (ILS) were performed in 671 baboons. Clinical histories were available for 531 (79%) of the animals. The EEG studies lasted 53 (±11) min, during which the baboons were lightly sedated with intramuscular ketamine doses of 5.6 (±0.8) mg. The animals were further classified according to electroclinical phenotypes recorded by scalp EEG: presence or absence of IEDs, seizures and photoparoxysmal or photoconvulsive responses. Effects of age, gender, and species on EEG phenotypes were compared using (Chi-square, two-sided, α<0.05). Sensitivity and specificity of IEDs and photosensitivity to detect a history of seizures was calculated. Generalized IEDs and photosensitivity were identified in 324 (49%) and 156 (23%) pedigreed baboons, respectively. Only photosensitivity was associated with gender, significantly increased in males. Otherwise, while IEDs were marginally more prevalent among males, there were no other significant associations of IEDs or photosensitivity with age or subspecies. Photosensitivity was significantly associated with IEDs, with demonstrating a possible association with gender and subspecies. Of 531 baboons with histories of clinical events, 91 (17%) had witnessed seizures and 269 (51%) were asymptomatic. IEDs demonstrated sensitivity and specificity of 62% and 57%, and photosensitivity of 40% and 83%, for prediction of seizures, respectively. While these EEG findings mirror the high prevalence of seizures in the colony, the sensitivity and specificity of scalp EEG may have been affected by ketamine's ability to lower the threshold for IEDs and seizures, particularly in animals predisposed to epilepsy. Photosensitivity provides a specific biological marker for epilepsy in future epidemiological, genetic, behavioral and histopathological studies.

Epidemiology and characterization of seizures in a pedigreed baboon colony.

This study evaluated the incidence, prevalence, and clinical features of seizures in a pedigreed captive colony of baboons. The association of seizures with subspecies, age, sex, and various clinical features was assessed. Records for 1527 captive, pedigreed baboons were reviewed, and 3389 events were identified in 1098 baboons. Of these events, 1537 (45%) represented witnessed seizures, whereas the remaining 1852 presented with craniofacial trauma or episodic changes in behavior that were suggestive, but not diagnostic, of seizure activity. Seizures were generalized myoclonic or tonic-clonic, with two thirds of the events witnessed in the morning. Seizure onset occurred in adolescence (age, 5 y), with an average of 3 seizures in a lifetime. The incidence and prevalence of seizures were 2.5% and 26%, respectively, whereas the prevalence of recurrent seizures (that is, epilepsy) was 15%. Seizures were more prevalent in male baboons, which tended to present with earlier onset and more seizures over a lifetime than did female baboons. Seizures were equally distributed between the subspecies; age of onset and seizure recurrences did not differ significantly between subspecies. Clinical features including age of onset, characteristics, and diurnal presentation of seizures in baboons suggested similarities to juvenile myoclonic epilepsy in humans. Facial trauma may be useful marker for epilepsy in baboons, but its specificity should be characterized.

Baboon model of generalized epilepsy: continuous intracranial video-EEG monitoring with subdural electrodes.

The baboon provides a natural non-human primate model for photosensitive, generalized epilepsy. This study describes an implantation procedure for the placement of subdural grid and strip electrodes for continuous video-EEG monitoring in the epileptic baboon to evaluate the generation and propagation of ictal and interictal epileptic discharges. Subdural grid, strip and depth electrodes were implanted in six baboons, targeting brain regions that were activated in functional neuroimaging studies during photoparoxysmal responses. The baboons were monitored with continuous video-EEG monitoring for 2-21 (mean 9) days. Although the animals were tethered, the EEG signal was transmitted wirelessly to optimize their mobility. Spontaneous seizures, interictal epileptic discharges (IEDs), and responses to intermittent light stimulation (ILS) were assessed. Due to cortical injuries related to the electrode implantation and their displacement, the procedure was modified. Habitual myoclonic and generalized tonic-clonic seizures were recorded in three baboons, all associated with a generalized ictal discharge, but were triggered multiregionally, in the frontal, parietal and occipital cortices. IEDs were similarly expressed multiregionally, and responsible for triggering most generalized spike-and-wave discharges. Generalized photoparoxysmal responses were activated only in one baboon, while driving responses recorded in all three photosensitive baboons were 2.5 times the stimulus rate. In contrast to previous intracranial investigations in this model, generalized ictal and interictal epileptic discharges were triggered by parietal and occipital, in addition to the frontocentral cortices. Furthermore, targeted visual areas responded differently to ILS in photosensitive than nonphotosensitive baboons, but further studies are required before mechanisms can be implicated for ILS-induced activation of the epileptic networks.

"Resting" CBF in the epileptic baboon: correlation with ketamine dose and interictal epileptic discharges.

BACKGROUND: Photosensitive epileptic (SZ) baboons demonstrate different cerebral blood flow (CBF) activation patterns from asymptomatic controls (CTL) during intermittent light stimulation (ILS). This study compares "resting" CBF between PS and CTL animals, and CBF correlations with ketamine dose and interictal epileptic discharges (IEDs) between PS and CTL animals. METHODS: Continuous intravenous ketamine was administered to eight PS and eight CTL baboons (matched for gender and weight), and maintained at subanesthetic doses (4.8-14.6 mg/kg/hr). Three resting H(2)(15)O-PET studies were attempted in each animal (CTI/Siemens HR+ scanner). Images were acquired in 3D mode (63 contiguous slices, 2.4mm thickness). PET images were co-registered with MRI images (3T Siemens Trio, T1-weighted 3D Turboflash sequence, TE/TR/TI=3.04/2100/785 ms, flip angle=13 degrees ). EEG was used to monitor depth of sedation and for quantification of IED rates. Regional CBF was compared between PS and CTL groups and correlations were analyzed for ketamine dose and IED rates. RESULTS: When subsets of animals of either group, receiving similar doses of ketamine were compared, PS animals demonstrated relative CBF increases in the occipital lobes and decreases in the frontal lobes. Correlation analyses with ketamine dose confirmed the frontal and occipital lobe changes in the PS animals. The negative correlations of CBF with ketamine dose and IED rate overlapped frontally. While frontal lobe CBF was also negatively correlated with IED rate, positive correlations were found in the parietal lobe. CONCLUSIONS: "Resting" CBF differs between PS and CTL baboons. Correlation analyses of CBF and ketamine dose reveal that occipital lobe CBF increases and frontal lobe in PS animals are driven by ketamine. While frontal lobe CBF decreases may be related to ketamine's propensity to activate IEDs, positive CBF correlations with IED rate suggest involvement of the parietal lobes in their generation.