# Myo-inositol elevation as an in vivo marker of reactive gliosis in pediatric Friedreich ataxia: evidence from HERMES-edited MR spectroscopy

## TL;DR

Elevated myo-inositol in motor cortices of children with Friedreich ataxia suggests early reactive gliosis, offering a potential biomarker for disease progression.

## Contribution

First in vivo measurement of glutathione and GABA in pediatric Friedreich ataxia using HERMES-edited MRS, identifying myo-inositol as a novel biomarker.

## Key findings

- No significant differences in glutathione or GABA+ between FRDA patients and controls.
- Significantly reduced tNAA/mI ratio in FRDA, driven by elevated myo-inositol in motor cortices.
- Myo-inositol elevations suggest reactive gliosis without significant neuronal loss in pediatric FRDA.

## Abstract

•First in vivo glutathione (GSH) and GABA measurement in pediatric Friedreich ataxia using HERMES-edited MRS.•No significant group-level differences in GSH or GABA+, despite strong rationale for oxidative and inhibitory dysfunction in FRDA.•Significant reduction in the tNAA/mI ratio in FRDA, driven by elevated myo-inositol rather than reduced tNAA (tNAA not significant, p = 0.150).•Myo-inositol elevations are significant in both motor cortices (Bonferroni-corrected), with a trend in cerebellum (pcorr = 0.054).

First in vivo glutathione (GSH) and GABA measurement in pediatric Friedreich ataxia using HERMES-edited MRS.

No significant group-level differences in GSH or GABA+, despite strong rationale for oxidative and inhibitory dysfunction in FRDA.

Significant reduction in the tNAA/mI ratio in FRDA, driven by elevated myo-inositol rather than reduced tNAA (tNAA not significant, p = 0.150).

Myo-inositol elevations are significant in both motor cortices (Bonferroni-corrected), with a trend in cerebellum (pcorr = 0.054).

Friedreich ataxia (FRDA) is a rare neurodegenerative disorder caused by frataxin deficiency and is characterized by mitochondrial dysfunction, oxidative stress, and progressive motor dysfunction. Most in vivo MRS work in FRDA has focused on the cerebellum, brainstem/pons, and spinal cord, consistently reporting abnormalities in the neuronal marker N-acetylaspartate (NAA) and the glial metabolite myo-inositol (mI). To our knowledge, the NAA/mI ratio in the primary motor cortex has not been reported in FRDA, particularly in pediatric cohorts. Additionally, in vivo edited MRS measurements of the inhibitory neurotransmitter γ-aminobutyric acid (GABA+ (GABA + macromolecular contributions)) in FRDA have not yet been reported and GSH has been examined only rarely in FRDA and, to our knowledge, has not been studied in the motor cortex in either adult or pediatric cohorts.

To assess GSH, GABA+, NAA, and mI across cerebellum and motor cortices in pediatric FRDA using HERMES-edited MRS.

We acquired HERMES MRS data from 16 children with FRDA and 15 age-matched controls. Tissue-corrected metabolite estimates were obtained using LCModel and voxel-based tissue segmentation. Linear mixed models (LMMs) were used to evaluate group and region effects, with subject as a random effect.

LMMs revealed no significant group differences in tissue-corrected GSH or GABA + . In contrast, the tNAA/mI ratio was significantly reduced in FRDA (p < 0.001), driven by elevated mI (p < 0.001), while tNAA did not differ between groups (p = 0.150). ROI-specific analyses showed higher mI in FRDA in both motor cortices after Bonferroni correction, with a non-significant trend in cerebellum (pcorr = 0.054).

These findings support a model of early reactive gliosis in pediatric FRDA, indexed by elevated mI and occurring without statistically significant neuronal loss, (acknowledging that significant reductions in tNAA may require larger samples to resolve), and extend prior cerebellar-focused work to the primary motor cortex. While GSH and GABA + did not differ between groups, the observed mI elevations highlight myo-inositol as a practical in vivo biomarker of astrocytic activation and a candidate marker for disease progression in FRDA. Longitudinal studies are needed to confirm its sensitivity to clinical trajectory and therapeutic response.