PP05.7 – 2639: Horizontal gaze palsy with progressive scoliosis (HGPPS): The role of brain MRI and diffusion tensor imaging in diagnosis

Introduction Horizontal gaze palsy with progressive scoliosis (HGPPS) is an autosomal recessive disorder characterized by congenital absence of conjugate horizontal eye movements and progressive scoliosis. It is caused by mutations in ROBO3, which plays an important role in midline crossing of selected axonal paths during embryonic stages. Patients A 12-year-old girl was referred with abnormal head movements and thoracolumbar scoliosis. Parents were first cousins. Her parents recognized abnormal eye movements and head titubation and progressive scoliosis, at the age of 1 y, and 7 y respectively. Physical examination revealed mild intellectual disability (ID), nystagmus, horizontal gaze palsy, head titubation and thoracolumbar scoliosis. A 4-year-old sister had scoliosis and titubation after the age of 2 years. She was born at term with a birth-weight of 3000 g via C/S due to breech presentation. She had developmental delay and unsteady gait. Physical examination revealed mild ID, bilateral horizontal gaze palsy, in toeing and scoliosis. MRI showed hypoplasia of the brainstem with a so called “butterfly” medulla oblongata and midsagittal cleft extending ventrally from the 4th ventricle, called as “split pons”. Along with the history and physical examination findings, this characteristic appearance led us to the diagnosis of HGPPS. Diffusion tensor imaging and fiber tractography obtained at 3T with 30 gradient encoding directions depicted absence of decussation of brainstem tracts. In this presentation, we aim to document neurologic and high-resolution MRI and DTI/fiber tractography findings of these siblings with HGPPS, a very rare, but also diagnosed straightforward disease. Robo3 mutation analysis is pending. Conclusion Recognizing typical neuroimaging pattern combined with the clinical picture characterized by gaze palsy and scoliosis are clues to consider HGPPS and Robo3 mutations. The age at presentation of scoliosis and severity differ in two siblings reflecting intra-familial clinical variability in this novel clinical entity.