Abstracts

Rationale: ECHS1 Deficiency (ECHS1D) is a rare Leigh syndrome-like disorder that lacks effective treatments. Loss of function mutations impair the activity of short-chain enoyl-CoA hydratase (ECHS1), which oxidizes short-chain fatty acids and branched-chain amino acids (valine, leucine, isoleucine) within mitochondria. ECHS1D presents early in life with severe developmental delays/regressions, hypotonia, and dystonia. Throughout the course of disease, patients develop basal ganglia lesions and progressive epilepsy. The pathogenesis of disease remains unknown; however, inflammation and toxic valine metabolite accumulation are hypothesized to drive symptom progression.

Methods:
A novel mouse model was generated that possesses a disease-associated knock-in allele and a knock-out allele. ECHS1 expression was measured by western blot. Under basal conditions, wireless telemetry devices were used to measure EEG and EMG. Power band analysis and sleep staging were also performed. Seizure susceptibility was assessed using pentylenetetrazol (PTZ) in a low-dose kindling paradigm. To determine if excess valine contributes to disease progression, mice were given a diet containing a 3% increase in valine and seizure susceptibility was again tested. Finally, mice were challenged with lipopolysaccharide (LPS) one month prior to PTZ induction to test if inflammation worsens the epileptic phenotype.









Results: Under standard conditions, ECHS1D mice had significantly reduced ECHS1 expression, which did not impact survival or development. EEG analysis showed that ECHS1D mice had generalized slowing marked by increased delta and theta power, specifically during wake periods. Compared to WT mice, ECHS1D mice spent significantly more time in active wake and less time in slow wave sleep, while inactive wake and paradoxical sleep were unaffected. ECHS1D mice also had significantly increased epileptiform discharges across the recording period. Following PTZ treatment, WT mice were seizure free while ECHS1D mice developed progressive seizures that resulted in 60% lethality. Excess dietary valine substantially worsened seizure susceptibility in ECHS1D mice, where 0% survived to the end of the study. In contrast, WT mice were unaffected by valine supplementation. Following LPS treatment, ECHS1D mice had reduced survival and failure to thrive, while WT mice fully recovered. In the surviving ECHS1D mice, seizure progression was exacerbated, resulting in 75% lethality from PTZ-induced seizures. LPS treatment did not induce seizures in WT mice.

Conclusions: In conclusion, we developed a model of ECHS1D that recapitulates features of human disease and identified novel neurophysiological biomarkers. Our findings support the hypotheses that dietary valine and inflammation contribute to disease progression. Future studies will use this model to further investigate the cellular changes underlying the epileptic phenotype to support the development of therapeutics.

Funding: This work was supported by funding from ECHS1 family foundations and mouse model generation was supported by the NIH Precision Genetics grant U54ODO30187.