A homozygous activating ATAD1 mutation impairs postsynaptic AMPA receptor trafficking 2 and causes a lethal encephalopathy with congenital stiffness

55 Members of the AAA+ superfamily of ATPases are involved in the unfolding of proteins and 56 disassembly of protein complexes and aggregates. ATAD1 encoding the ATPase family, AAA+ 57 domain containing 1-protein Thorase plays an important role in the function and integrity of 58 mitochondria and peroxisomes. Postsynaptically, Thorase controls the internalization of 59 excitatory, glutamatergic AMPA receptors (AMPAR) by disassembling complexes between the 60 AMPAR-binding protein, GRIP1, and the AMPAR subunit GluA2. Using whole-exome 61 sequencing, we identified a homozygous frameshift mutation in the last exon of ATAD1 62 [c.1070_1071delAT; p.(His357Argfs*15)] in three siblings who presented with a severe, lethal 63 encephalopathy associated with stiffness and arthrogryposis. Biochemical and cellular 64 analyses show that the C-terminal end of Thorase mutant gained a novel function which 65 strongly impacts its oligomeric state, reduces stability or expression of a set of Golgi, 66 peroxisomal and mitochondrial proteins and affects disassembly of GluA2AMPAR and Thorase 67 oligomer complexes. Atad1 -/- neurons expressing Thorase mutant His357Argfs*15 display reduced 68 amount of GluA2 at the cell surface suggesting that the Thorase mutant may inhibit the 69 recycling back and/or reinsertion of AMPARs to the plasma membrane. Taken together, our 70 molecular and functional analyses identify an activating ATAD1 mutation as a new cause of 71 severe encephalopathy and congenital stiffness.