Clinicians and Geneticists studying atrophic changes in the brain and development due to the PAX6 gene mutation especially in anridia condition in human and preclinical models.The PAX6 gene encodes a highly conserved transcription factor that is expressed in the developing eye, brain, spinal cord and pancreas, and is required for various aspects of anatomical and functional development. Knocking out PAX6 from mouse genome results in in the absence of eye or so called Small eye (Sey) mouse. Heterozygous loss-of-function mutations of PAX6 are causal for aniridia in humans. While the effects of PAX6 mutations on ocular development have been well characterized in human and mouse, the implications of these mutations on brain structure remain poorly understood. Previous studies have identified structural abnormalities in fiber tracts and subcortical structures in the brain including corpus callosum, anterior and posterior commissures, pineal gland and probst bundles in persons with aniridia using magnetic resonance imaging^1-2 (MRI). The purpose of the current study is to investigate whether structural brain abnormalities observed in human patient are still present or similar in the Small Eye Neu (PAX6^{Sey Neu/+}) mouse model of the disorder using voxel based morphometry (VBM) MRI and histological measures of brain structure.All animal procedures were approved by the IACUC of the UGA. Male and female groups (n=8 each) of 4-5 months old from Sey and Wild type mice were imaged on a 7T Agilent MRI system using a 38 mm quadrature and 10 mm surface coils. Animals were administered contrast agent (40 mg/kg, MnCl₂) via i.p. injection for three consecutive days prior to 2D T₁-weighted spin echo manganese enhanced imaging (MEMRI). (MEMRI, TR/TE, 500/13 ms, 256 x256 matrix size, signal averaging of 4, FOV 30x30 mm). A T2-weighted 3D images were acquired with following parameters: fast spin echo T₂ weighted MRI, TR/TE 700/30 ms, with FOV of 20 x 20 x 20 mm, 256x 256 x 256 matrix size, 4 averages, scan time 45 minutes for VBM study. For VBM analysis, all 3D images were skull stripped and aligned with each other by SPM8 and co-registered with mouse brain template³. Segmentation were performed on those images to obtain three different WM, GM and CSF class images and these images were smoothed with a 0.2-mm FWHM Gaussian kernel and compared with two-sample t-tests. (p<0.05 cluster size of 100 were used and widely accepted as statistically significance). Histological 8 PAX6^{Sey Neu/+} and 8 wild-type litter mates underwent structural MRI and brain tissue was collected for each animal (n=16). Brains from all animals were fixed in 4% paraformaldehyde and paraffin sectioned, then stained with luxol fast blue, eosin and cresyl violet.Our results showed that there was a significant morphological changes in volume of brain in a few regions of interest (ROIs) analyzed by manual tracing of mice brain. VBM also analysis confirmed significant anatomical differences in discrete grey and white matter and CSF structures (increased volume in pituitary, cortex, hippocampus, olfactory bulb and cerebellum in Sey mouse) (Fig 1). Moreover, white matter differences were detected in superior and middle cerebellar peduncles and posterior corpus callosum forceps. Histological staining were able to confirm our MRI findings and demonstrated morphological differences in olfactory bulb, hippocampus, cerebellum, corpus callosum, anterior commissure, lateral septal nuclei, and stria medullaris of thalamus.(Fig 2 (a,b)The results of this study identifies for the first time, a significant morphological changes in the brain due to the consequences of PAX6 haploinsufficiency in adult rodents, when compared to the neuroanatomical abnormalities observed in humans with PAX6 mutations, provides insight into the role of PAX6 in the development and function of the brain.