7 Tesla MRI Reveals Brain Structural Abnormalities and Neural Plasticity in RPGR-Related Retinitis Pigmentosa

Objectives: The purpose was to quantitatively examine brain structures using 7 Tesla MRI in the presence of visual loss caused by retinitis pigmentosa (RP) related to retinitis pigmentosa GTPase regulator (RPGR) gene pathogenic variants. Methods: Twelve male patients with RP (mean visual acuity 0.4) related to confirmed RPGR pathogenic variants and fifteen healthy volunteers were examined with 7 Tesla MRI of the brain. Measures of the lateral geniculate nucleus (LGN) volume were performed manually by three independent investigators (radiologists) using ITK-SNAP (Insight Segmentation and Registration Toolkit) software. Other brain structures were evaluated using the open-source automated software package FreeSurfer. Prior to the 7 Tesla MRI, patients underwent an ophthalmic examination and a 1.5 Tesla MRI. Results: The mean LGN volume (right-100 mm³, left-96 mm³) and left lingual gyrus volume (6162 mm³) were significantly lower in RPGR patients in comparison to the control group (129 mm³, 125 mm³, and 7310 mm³, respectively), whilst some brain regions related to other sensory information such as the left isthmus cingulate (3690 mm³) and entorhinal cortex (right-1564 mm³, left 1734 mm³) were significantly or almost significantly higher in the RPGR group than in the control group (2682 mm³, 960 mm³, and 1030 mm³, respectively). Moreover, compared to the control group, the RPGR group's thalamus-to-LGN ratio was substantially higher. Conclusions: The use of the 7 Tesla MRI revealed numerous structural abnormalities of the visual pathway in patients with RPGR-related RP. The reorganization of the structures of the brain demonstrated in patients with RPGR-related RP reveals a certain degree of plasticity in response to visual loss. These findings may help improve diagnostic and therapeutic strategies for RP patients and contribute to the development of precision medicine.