Objectives: The aim of this study was to explore the relationship between cognitive dysfunction, neurodegeneration, and genetic factors among multiple sclerosis (MS) patients. Methods: Fifty patients of definite MS were included. Physical disability was assessed by expanded disability status scale (EDSS). Cognitive functions were assessed by using the Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS). For each eye, optical coherence tomography (OCT) was used to track thickness of retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC), respecting the previous history of optic neuritis (ON). All patients were genotyped for glutamate N-methyl-D-aspartate receptors (NMDARs). Results: A statistically significant negative correlation was found between scores of EDSS and each of neuropsychological tests scores and thickness of both RNFL and GCC. The predictor for progressive disability assessed by EDSS was Symbol Digit Modalities Test (SDMT) (P = 0.021), that is dependent on the educational level of the patients (P = 0.016). A statistically significant positive correlation was found between scores of all neuropsychological tests and the thickness of both RNFL and GCC. Eighty-three percent of MS patients with CC genotype reported previous attacks of ON with significant thinning in RNFL and GCC despite their higher cognitive performance in comparison to other genotypes. Discussion: Deficit in information processing speed measured by SDMT is a predictor of early progressive disability in MS patients. Thinning of RNFL and GCC is a potential biomarker for cognitive and physical disability in MS. The CC genotype of glutamate NMDAR gene has a divergent effect on visual and cognitive functions.
Keywords: EDSS; Multiple sclerosis; NMDAR gene; optic neuritis; optical coherence tomography; symbol digit modalities test.