Objective:

To identify the causative mutation for FCMTE in families and to investigate the impact of PKHD1L1 mutation on cortical excitability and its potential mechanism. 

Background:

Familial cortical myoclonic tremor and epilepsy (FCMTE) is a rare hereditary epilepsy syndrome characterized by adult-onset distal tremor-like cortical myoclonus, with or without generalized tonic–clonic seizures. The exact pathophysiology of FCMTE remains unclear, although cortical hyperexcitability is thought to contribute to both the tremor and epileptic manifestations of the disorder. 

Design/Methods:

We have employed modern approaches—including whole-exome sequencing, gene-edited PKHD1L1 knock-in rat models, molecular dynamics simulations, RNA-proteomics, ethological analyses, neuroelectrophysiology, immunohistochemistry, and immunofluorescence—to systematically investigate the molecular pathogenesis of PKHD1L1 in FCMTE.

Results:

We identified two mutations within PKHD1L1 in three Chinese families with FCMTE for the first time: c.2602A>T (p. T868S) in two families and a mutation in 3′ untranslated region of PKHD1L1 (c. *801G>A) in one family. Subsequently, we generated a PKHD1L1p.L867S knock-in rat, orthologous to the human PKHD1L1 p. T868S, using CRISPR/Cas9. Studies on this model revealed phenotypic similarities to human FCMTE, including increased susceptibility to pentylenetetrazol-induced seizures, decreased latency of somatosensory evoked potential (p=0.004, 10.17±1.23 vs 12.25±1.40ms) and AFP (p=0.0039, 67.67 ± 20.46 vs 32.85 ±10.28 mV ) and threshold (p=0.0114, -25.76 ± 7 vs -41.23 ±10.05 mV) of AP, increased sEPSC frequency (p=0.0079, 2.37 ± 0.39 vs 3.39 ± 0.65 Hz) and calcium currents (p=0.039, -601.57 ± 161.38 vs -824.97 ± 165.63 pA ) in cortical neurons. Proteomics and transcriptomics studies unveiled enhanced PKA activity in PKHD1L1 +/- rats, and increased excitability in cortical neurons was ameliorated by PKA inhibitor, H89.

Conclusions:

We confirmed that PKHD1L1 mutation lead to calcium channel disturbance of cortical neurons via PKA activation. Our findings identify for the first time the pathogenesis of FCMTE and present a novel therapeutic target for treating epilepsy and tremor.