To explain the pathology of horizontal gaze in HGPPS, it is important to learn both from electrophysiologic and from radiologic studies in patients with HGPPS [8,9], as well as from animal studies on ROBO3 and its homologs [13,15], that fibers which fail to cross the midline can connect with ipsilateral targets. The gene discussed is ROBO3; the disease is horizontal gaze palsy with progressive scoliosis.