Reduction in retinal nerve fiber layer thickness in tuberous sclerosis complex

Optical coherence tomography detection of retinal neural loss in patients with tuberous sclerosis

PURPOSE

Tuberous Sclerosis (TS) is a rare, multisystem genetic disease caused by mutations in the TSC1 and TSC2 genes, leading to abnormalities in cell differentiation and proliferation. This study aimed to evaluate the neural integrity of individuals with TS by using Optical Coherence Tomography (OCT) to examine the peripapillary retinal nerve fiber layer (RNFL) thickness and the macular thickness in patients with TS and to compare with healthy controls.

METHODS

Peripapillary and macular OCT scans (Optopol Revo NX SD OCT) were performed on 41 eyes from 22 TS patients, divided into two groups based on the presence of retinal hamartomas, and compared to 20 eyes from a control group. The average peripapillary RNFL thickness was measured for each quadrant. The macular total thickness and ganglion cell layer (GCL) + inner plexiform layer (IPL) thickness were measured based on the Early Treatment Diabetic Retinopathy Study (ETDRS) map. All measurements were then compared between the groups and controls.

RESULTS

The TS group showed significantly reduced RNFL thickness and macular thickness when compared to the control group. Specifically, patients with retinal hamartomas exhibited an even more pronounced thinning of both RNFL and macular thickness.

CONCLUSIONS

These findings suggest that TS patients undergo significant changes in retinal neurodevelopment and experience axonal loss. This finding may have significant prognostic utility regarding central nervous system degeneration in TS, particularly among patients with retinal hamartomas. OCT may serve as a valuable tool for assessing axonal structural abnormalities in TS patients.

TRIAL REGISTRATION NUMBER

Not applicable.

OPTICAL COHERENCE TOMOGRAPHY AND INFRARED IMAGES OF ASTROCYTIC HAMARTOMAS NOT REVEALED BY FUNDUSCOPY IN TUBEROUS SCLEROSIS COMPLEX

PURPOSE

To detect, describe, and classify the morphologic characteristics of astrocytic hamartomas in tuberous sclerosis complex, using both spectral-domain optical coherence tomography (OCT) and infrared images.

METHODS

Ten subjects (20 eyes) with tuberous sclerosis complex underwent a complete ophthalmologic examination and multimodality imaging with spectral-domain OCT and infrared images. The imaging protocol included a 30°scan angle of the posterior pole and of the four quadrants. Line scans, detail, raster, and posterior pole patterns were used. The identified astrocytic hamartomas were described and characterized qualitatively and quantitatively.

RESULTS

Forty-four hamartomas were detected in 8 patients. In five cases, lesions were bilateral. Thirty of these hamartomas had not been revealed by previous ophthalmoscopy. Through multimodality imaging, it was possible to define multiple lesions with characteristic optical reflective qualities. All the 44 hamartomas were measured and morphologically characterized in terms of the type of tumor, retinal and/or vitreous involvement, calcifications, and posterior optical shadowing.

CONCLUSION

The combined imaging with spectral-domain OCT and infrared images improves the detection of hamartomas if compared with the spectral-domain OCT technique alone. Moreover, a new subtype of hamartoma is proposed to complete a previous classification based on OCT.

Molecular neurobiology of mTOR

Mammalian/mechanistic target of rapamycin (mTOR) is a serine-threonine kinase that controls several important aspects of mammalian cell function. mTOR activity is modulated by various intra- and extracellular factors; in turn, mTOR changes rates of translation, transcription, protein degradation, cell signaling, metabolism, and cytoskeleton dynamics. mTOR has been repeatedly shown to participate in neuronal development and the proper functioning of mature neurons. Changes in mTOR activity are often observed in nervous system diseases, including genetic diseases (e.g., tuberous sclerosis complex, Pten-related syndromes, neurofibromatosis, and Fragile X syndrome), epilepsy, brain tumors, and neurodegenerative disorders (Alzheimer's disease, Parkinson's disease, and Huntington's disease). Neuroscientists only recently began deciphering the molecular processes that are downstream of mTOR that participate in proper function of the nervous system. As a result, we are gaining knowledge about the ways in which aberrant changes in mTOR activity lead to various nervous system diseases. In this review, we provide a comprehensive view of mTOR in the nervous system, with a special focus on the neuronal functions of mTOR (e.g., control of translation, transcription, and autophagy) that likely underlie the contribution of mTOR to nervous system diseases.