Autism-associated SCN2A deficiency disrupts cortico-striatal circuitry in human brain assembloids
Profound autism spectrum disorder (ASD) is frequently attributable to single-gene mutations, with SCN2A (voltage-gated sodium channel NaV1.2) protein-truncating variants (PTVs) being one of the most penetrant. Although cortico-striatal circuitry is implicated as a key node in ASD, the impact of SCN2A deficiency on human neural circuits is unknown. Using the human cortico-striatal assembloid model, we show that the autism-causing PTV SCN2A-C959X impairs long-range cortical axonal projections, reduces striatal spine density, and attenuates excitatory cortical-striatal synaptic transmission. Surprisingly, these assembloids carrying the heterozygous SCN2A nonsense mutation exhibited pronounced network hyperexcitability, a human cell-specific phenotype not observed in Scn2a+/- mice, highlighting a human-specific circuit vulnerability. Collectively, our study unveils human circuit-specific dysfunctions of SCN2A deficiency and SCN2A-mediated ASD. HighlightsO_LIAxonal projections facilitate synapse formation and functional connectivity in human brain assembloids. C_LIO_LINaV1.2 is expressed along neuronal axons, extending to soma and dendrites in human brain assembloids. C_LIO_LISCN2A-C959X disrupts axonal projection patterns, impairs excitatory synaptic transmission, reduces spine density, and results in elevated neuronal excitability. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=90 SRC="FIGDIR/small/657036v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@6d5b1forg.highwire.dtl.DTLVardef@1795ecdorg.highwire.dtl.DTLVardef@13f0d7eorg.highwire.dtl.DTLVardef@8ee059_HPS_FORMAT_FIGEXP M_FIG C_FIG In briefO_ST_ABSSCN2A haploinsufficiency impairs cortico-striatal circuitry.C_ST_ABSSCN2A haploinsufficiency disrupts axon initial segment (AIS) integrity, leading to hyperexcitability (red arrow), reduced axon projections, and impaired synaptic transmission (decreased sEPSCs and altered network firing). These deficits result in dysfunction within the cortico-striatal circuitry.