Visual system involvement in patients with Friedreich's ataxia

Area of Science:

• Neuroscience
• Ophthalmology
• Genetics

Background:

• Optic neuropathy is common in mitochondrial disorders.
• Friedreich's ataxia (FRDA) is a recessive condition caused by frataxin deficiency, with poorly characterized optic neuropathy.
• Visual pathway involvement in FRDA is often underestimated.

Purpose of the Study:

• To investigate optic nerve and visual pathway involvement in Friedreich's ataxia (FRDA).
• To characterize the patterns and extent of visual system damage in FRDA patients.
• To differentiate FRDA-associated optic neuropathy from other mitochondrial optic neuropathies.

Main Methods:

• Studied 26 molecularly confirmed FRDA patients.
• Utilized visual field testing, optical coherence tomography (OCT), and pattern visual evoked potentials (P-VEPs).
• Employed diffusion-weighted imaging to assess optic radiations via apparent diffusion coefficients (ADC).

Main Results:

• All patients showed optic nerve involvement; OCT revealed reduced retinal nerve fiber layer thickness in all.
• P-VEPs were abnormal in approximately half of patients; advanced stages showed decreased visual acuity and optic disc pallor.
• Increased ADC values in optic radiations were observed in FRDA patients compared to controls.
• Retinal nerve fiber layer thickness, P-VEPs, and ADC values correlated with disease severity and progression markers.

Conclusions:

• Visual pathway involvement, including optic radiations, is consistently present and previously underestimated in FRDA.
• FRDA-associated optic neuropathy exhibits distinct characteristics compared to classic mitochondrial optic neuropathies, suggesting a different pathophysiology.
• Occasional Leber's hereditary optic neuropathy (LHON)-like presentations can occur in FRDA.