LAUSR

A 10-month-old boy presented with motor developmental delay, torticollis, bilateral abduction restriction (incomplete horizontal gaze palsy), and left lower motor neuron facial palsy. His brain MRI demonstrated brainstem malformations, including absent facial colliculi (Figure, A), clefting of the medulla and pons (Figure, B), butterfly configuration of the medulla (Figure, C), and concave dorsal pontine border (Figure, D). Genetic testing revealed a homozygous missense mutation (c.437G > C [p.Arg146Pro]) in exon 2 of the ROBO3 gene. Horizontal gaze palsy with progressive scoliosis (HGPPS1) results from axonal guidance signalling defects caused by ROBO3 mutations.1 The main symptoms include congenital horizontal gaze palsy, horizontal pendular nystagmus, and progressive scoliosis after 2 years of age. The radiologic differential for this hindbrain malformation is horizontal gaze palsy with progressive scoliosis-2, caused by mutation in the DCC gene.2 Children with HGPPS2 also demonstrate intellectual impairment and agenesis of the corpus callosum.2