In patient S188 with PM (−3.9 SD), bilateral polymicrogyria, DD, epilepsy, spastic tetraplegia, nystagmus, convergent strabismus and cryptorchidism we found two heterozygous de novo variants in two genes encoding ion channel subunits: KCNT1-NM_020822.3: c.1720G>A: p.(Glu574Lys) and GRIN1-NM_007327.4: c.1665G>T: p.(Met555Ile). Here, GRIN1 is linked to pathologic nystagmus.