We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific β-tubulin isotype III, result in a spectrum of human nervous system disorders we now call the TUBB3 syndromes. Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy. Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves, and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts. A knock-in disease mouse model reveals axon guidance defects without evidence of cortical cell migration abnormalities. We show the disease-associated mutations can impair tubulin heterodimer formation in vitro, although folded mutant heterodimers can still polymerize into microtubules. Modeling each mutation in yeast tubulin demonstrates that all alter dynamic instability whereas a subset disrupts the interaction of microtubules with kinesin motors. These findings demonstrate normal TUBB3 is required for axon guidance and maintenance in mammals.

Purpose-We aimed to characterize and grade the spectrum of foveal hypoplasia based on different stages of arrested development of the fovea. Grading was performed using morphological findings obtained by ultrahigh resolution spectral domain optical coherence tomography (UHR-OCT). Best corrected visual acuity (BCVA) was calculated for different grades. Design-Observational Case SeriesParticipants and Controls-Sixty-nine patients with foveal hypoplasia (albinism (n=34), PAX6 mutations (n=10), isolated cases (n=14), achromatopsia (n=11)) and 65 control subjects were examined.Methods-A 7x7mm retinal area was sampled using a 3-dimensional scanning protocol (743x75; AxB scans) with UHR-OCT (SOCT Copernicus HR, 3μm axial resolution). Gross morphological abnormalities were documented. B-scans at the fovea were segmented using a longitudinal reflectivity profile. Logarithm of Minimum Angle of Resolution (LogMAR) BCVA was obtained.Main Outcome Measures-Grading was based on presence or absence of foveal pit, widening of outer nuclear layer (ONL) and outer segment (OS) at the fovea. Quantitative measurements were performed for comparing atypical foveal hypoplasia in achromatopsia. BCVA was compared to the grade of foveal hypoplasia Results-Four grades of foveal hypoplasia were distinguished grade 1: shallow foveal pit, presence of ONL widening, presence of OS lengthening; grade 2: grade 1 but absence of foveal pit, grade 3: grade 2 but absence of OS lengthening; grade 4: grade 3 but absence of ONL widening). There was significant difference in visual acuity (VA) associated with each grade (p<0.0001). Grade 1 was associated with the best VA (median VA = 0.2), while grade 2, 3 and 4 was associated with progressively poorer VA with a median VA of 0. 44, 0.60 and 0.78 Correspondence and address for reprints: Professor Irene Gottlob (ig15@le.ac.uk) HHMI Author ManuscriptHHMI Author Manuscript HHMI Author Manuscript respectively. The atypical features seen with foveal hypoplasia associated with achromatopsia were characterized by decreased retinal (RT) and ONL thickness and deeper foveal depth (FD).Conclusions-We have developed a structural grading system for foveal hypoplasia based on the stage at which foveal development was arrested, which helps to provide a prognostic indicator for VA and is applicable in a range of disorders associated with foveal hypoplasia. Atypical foveal hypoplasia in achromatopsia shows different characteristics.Normal foveal development occurs in stages where the pit formation for the incipient fovea starts at fetal week 25 and the excavation is complete 15-45 months after birth. 1 Disruption of this developmental process leads to foveal hypoplasia which is a characteristic morphological abnormality associated with conditions such as albinism, PAX6 mutations or it may occur in isolation. [2][3][4][5] With the advent of optical coherence tomography (OCT) it is now possible to document the varying degrees of foveal hypoplasia which are likely to represent the different stages of arrested deve...

The mechanisms controlling axon guidance are of fundamental importance in understanding brain development. Growing corticospinal and somatosensory axons cross the midline in the medulla to reach their targets and thus form the basis of contralateral motor control and sensory input. The motor and sensory projections appeared uncrossed in patients with horizontal gaze palsy with progressive scoliosis (HGPPS). In patients affected with HGPPS, we identified mutations in the ROBO3 gene, which shares homology with roundabout genes important in axon guidance in developing Drosophila , zebrafish, and mouse. Like its murine homolog Rig1/Robo3, but unlike other Robo proteins, ROBO3 is required for hindbrain axon midline crossing.

We identified homozygous truncating mutations in HOXA1 in three genetically isolated human populations. The resulting phenotype includes horizontal gaze abnormalities, deafness, facial weakness, hypoventilation, vascular malformations of the internal carotid arteries and cardiac outflow tract, mental retardation and autism spectrum disorder. This is the first report to our knowledge of viable homozygous truncating mutations in any human HOX gene and of a mendelian disorder resulting from mutations in a human HOX gene critical for development of the central nervous system.