Is retina affected in Huntington's disease? Is optical coherence tomography a good biomarker?

Optical coherence tomography measurements in Huntington's disease: a systematic review and meta-analysis

BACKGROUND

A connection has been established between ocular structural changes and various neurodegenerative diseases. Several studies utilizing optical coherence tomography (OCT) have detected signs of ocular structural alterations among individuals with Huntington's disease (HD). The inconsistent results reported in the literature regarding alterations in the retina and choroid encouraged us to conduct this systematic review and meta-analysis to accumulate the findings.

METHODS

A systematic search was carried out in three electronic databases (PubMed, Embase, Scopus) to find studies reporting OCT measurements in HD cases compared with healthy controls (HC). A fixed-effects or random-effects meta-analysis was conducted according to the detected heterogeneity level. Furthermore, subgroup and sensitivity analyses, meta-regression, and quality assessment were performed.

RESULTS

Eleven studies were included in the systematic review and 9 studies with a total population of 452 participants (241 cases, and 211 HC) underwent meta-analysis. Results of the analysis denoted that subfoveal choroid had a significantly reduced thickness in HD eyes compared to HC (p < 0.0001). Moreover, our analysis indicated that HD cases had a significantly thinner average (p = 0.0130) and temporal peripapillary retinal nerve fiber layer (pRNFL) (p = 0.0012) than HC. However, subjects with pre-HD had insignificant differences in average (p = 0.44) and temporal pRNFL thickness (p = 0.33) with the HC group.

CONCLUSION

Results of the current systematic review and meta-analysis revealed the significant thinning of average and temporal pRNFL and subfoveal choroid in HD compared to HC. However, OCT currently might be considered insensitive to be applied in the pre-HD population at least until further longitudinal investigations considering variables such as the duration between OCT measurement and disease onset validating OCT as a routine diagnostic tool in HD clinics.

[Retinal OCT biomarkers and neurodegenerative diseases of the central nervous system beyond Alzheimer's disease]

BACKGROUND

Optical coherence tomography (OCT) biomarkers are increasingly used by neurologists, psychiatrists, and ophthalmologists for the diagnosis, prognosis, and follow-up of neurodegenerative diseases. Long-term data on OCT biomarkers of selected primary and secondary neurodegenerative diseases of the central nervous system (CNS), such as multiple sclerosis (MS) or Parkinson's disease, are already available in part. In addition, there are rare neurodegenerative diseases with early disease onset that may show OCT abnormalities.

METHODS

A literature review on the association of OCT biomarkers with neurodegenerative diseases of the CNS beyond Alzheimer's disease is presented. Parkinson's disease, MS, Friedreich's ataxia, Huntington's disease, spinocerebellar ataxia, and lysosomal storage diseases are addressed.

RESULTS

Relevant OCT biomarkers of neurodegenerative diseases are the macular ganglion cell inner plexiform layer (GCIPL) and the peripapillary retinal nerve fiber layer (pRNFL) thickness. Different sectors may be affected depending on the disease entity in addition to global pRFNL reduction. OCT‑angiography (OCT-A) is also increasingly used as a biomarker in neurodegenerative diseases.

CONCLUSION

Optical coherence tomography biomarkers are used in an interdisciplinary context. Retinal pathologies should be excluded by an ophthalmologist. While OCT biomarkers are increasingly used clinically in MS, the benefit in other neurodegenerative diseases, especially the rare ones, is less well documented. Further longitudinal studies are required.

Metabolomics: An Emerging "Omics" Platform for Systems Biology and Its Implications for Huntington Disease Research

Huntington's disease (HD) is a progressive, fatal neurodegenerative disease characterized by motor, cognitive, and psychiatric symptoms. The precise mechanisms of HD progression are poorly understood; however, it is known that there is an expansion of the trinucleotide cytosine-adenine-guanine (CAG) repeat in the Huntingtin gene. Important new strategies are of paramount importance to identify early biomarkers with predictive value for intervening in disease progression at a stage when cellular dysfunction has not progressed irreversibly. Metabolomics is the study of global metabolite profiles in a system (cell, tissue, or organism) under certain conditions and is becoming an essential tool for the systemic characterization of metabolites to provide a snapshot of the functional and pathophysiological states of an organism and support disease diagnosis and biomarker discovery. This review briefly highlights the historical progress of metabolomic methodologies, followed by a more detailed review of the use of metabolomics in HD research to enable a greater understanding of the pathogenesis, its early prediction, and finally the main technical platforms in the field of metabolomics.

Retina Oculomics in Neurodegenerative Disease

Ophthalmic biomarkers have long played a critical role in diagnosing and managing ocular diseases. Oculomics has emerged as a field that utilizes ocular imaging biomarkers to provide insights into systemic diseases. Advances in diagnostic and imaging technologies including electroretinography, optical coherence tomography (OCT), confocal scanning laser ophthalmoscopy, fluorescence lifetime imaging ophthalmoscopy, and OCT angiography have revolutionized the ability to understand systemic diseases and even detect them earlier than clinical manifestations for earlier intervention. With the advent of increasingly large ophthalmic imaging datasets, machine learning models can be integrated into these ocular imaging biomarkers to provide further insights and prognostic predictions of neurodegenerative disease. In this manuscript, we review the use of ophthalmic imaging to provide insights into neurodegenerative diseases including Alzheimer Disease, Parkinson Disease, Amyotrophic Lateral Sclerosis, and Huntington Disease. We discuss recent advances in ophthalmic technology including eye-tracking technology and integration of artificial intelligence techniques to further provide insights into these neurodegenerative diseases. Ultimately, oculomics opens the opportunity to detect and monitor systemic diseases at a higher acuity. Thus, earlier detection of systemic diseases may allow for timely intervention for improving the quality of life in patients with neurodegenerative disease.