Additionally, we found that the total cystatin C concentration measurement generated superior diagnostic accuracy, indicating that this may be the more efficacious measure of cystatin C. An assessment of the diagnostic parameters of CSF cystatin C concentration revealed that the sensitivity of cystatin C for differentiating ALS patients from disease controls is low for all cutoff values but it displays high levels of specificity and, therefore, cystatin C can only identify a small subset of ALS patients. This evidence concerns the gene CST3 and amyotrophic lateral sclerosis.