Movement disorder in GNAO1 encephalopathy associated with gain-of-function mutations

Objective: To define molecular mechanisms underlying the clinical spectrum of epilepsy and movement disorder in individuals with de novo mutations in the GNAO1 gene. Methods: We identified all GNAO1 mutations reported in individuals with epilepsy (early infantile epileptiform encephalopathy 17) or movement disorders through April 2016; 15 de novo mutant alleles from 25 individuals were introduced into the Gα o subunit by site-directed mutagenesis in a mammalian expression plasmid. We assessed protein expression and function in vitro in HEK-293T cells by Western blot and determined functional Gα o -dependent cyclic adenosine monophosphate (cAMP) inhibition with a coexpressed α 2A adrenergic receptor. Results: Of the 15 clinical GNAO1 mutations studied, 9 show reduced expression and loss of function (LOF; 50 values for α 2A adrenergic receptor–mediated inhibition of cAMP. The GNAO1 LOF mutations are associated with epileptic encephalopathy while GOF mutants (such as G42R, G203R, and E246K) or normally functioning mutants (R209) were found in patients with movement disorders with or without seizures. Conclusions: Both LOF and GOF mutations in Gα o (encoded by GNAO1 ) are associated with neurologic pathophysiology. There appears to be a strong predictive correlation between the in vitro biochemical phenotype and the clinical pattern of epilepsy vs movement disorder.