Abstracts

Rationale: Structural brain abnormalities, including cortical dysplasia and neuronal heterotopias, have been reported in individuals with pyridoxine-dependent epilepsy (PDE). PDE is caused by mutations in aldehyde dehydrogenase 7A1 (ALDH7A1), also known as antiquitin. How antiquitin dysfunction leads to neuronal migration defects is unknown. In this study, we analyzed control developing human and murine brain, as well as tissue from a child with PDE, to determine the normal distribution of antiquitin expression, its distribution in PDE, and associated neuronal migration abnormalities. Methods: Formalin-fixed human control and PDE brain sections were subjected to routine histopathology as well as fluorescence immunohistochemistry studies. Brain tissue frozen at autopsy was utilized for Western blot analysis. Comparative studies of antiquitin distribution were performed in mouse brain sections obtained at E14.5, P0, and P20. Results: Histologic analysis of PDE cortex revealed areas of abnormal tangential neuronal organization with microcolumns suggestive of type Ia focal cortical dysplasia. Neuronal heterotopias were identified in subcortical white matter, as well as cortical astrogliosis, hippocampal sclerosis with severe neuronal loss, and patchy gliosis of the basal ganglia. Interneuron density and distribution in PDE cortex was not altered, although total GAD-67 expression was reduced. In control human and mouse cortex, cytoplasmic antiquitin immunofluorescence was identified in astrocytes, ependyma, and choroid plexus, but not in neurons. In PDE cortex, antiquitin immunofluorescence was greatly attenuated, with perinuclear accumulation in astrocytes. Co-expression of antiquitin with the radial glial marker Sox2, but not the immature neuronal marker DCX, was identified in the developing mouse brain. Conclusions: Antiquitin (ALDH7A1) is expressed in glial cells in the brain, and its dysfunction in PDE is associated with neuronal migration defects. These structural brain abnormalities persist despite postnatal pyridoxine supplementation and may contribute to seizures and neurodevelopmental impairments in this disorder.