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Horizontal gaze palsy with progressive scoliosis (HGPPS) is a rare autosomal recessive disorder characterized by the congenital absence of horizontal gaze, progressive scoliosis, and failure of the corticospinal and somatosensory axon tracts to decussate in the medulla. HGPPS is caused by mutations of the ROBO3 gene, which encodes a protein that shares homology with the roundabout family of transmembrane receptors that are important in axon guidance and neuronal migration. To date, over 15 mutations have been found in consanguineous families of Greek, Italian, Turkish, Pakistani, Saudi Arabian, and Indian descent. To detail clinical, cerebral magnetic resonance imaging (MRI) and genetic findings of ten HGPPS patients from four unrelated Tunisian families. Four unrelated consanguineous Tunisian families with a total of ten patients suffering from horizontal gaze palsy with progressive scoliosis. Genetic linkage analysis and direct sequencing of the ROBO3 gene. All patients shared similar clinical gaze movement abnormalities and variable degrees of scoliosis. Four distinct homozygous mutations were identified. This study extends the molecular spectrum of the ROBO3 gene and the geographic origin of patients with ROBO3 gene mutations, and underlines the homogeneity of the motor ocular syndrome whatever type of mutation is encountered.