Background: Due to high prevalence of cognitive impairment in Huntington's disease (HD) gene mutation carriers, even before onset of motor symptoms, cognitive screening is important for the optimal management of patients. The Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) are widely used, but the validity for HD has only been evaluated in few studies with important limitations.

Objective: To evaluate the discriminative validity of the MMSE and the MoCA for the assessment of cognitive dysfunction in HD gene mutation carriers, independently of motor manifestation and furthermore, to report estimated probabilities for cognitive impairment with different score ranges on the MMSE and the MoCA.

Methods: 106 pre-motor-manifest and motor-manifest HD gene mutation carriers and 40 non-HD gene mutation carriers were administered the MMSE, the MoCA, and an extensive neuropsychological battery with operationalized criteria for cognitive impairment. The same physician and the same neuropsychologist performed all examinations; blinded to one another.

Results: The area under the receiver operating characteristic (ROC) curve was 0.70 for the MMSE and 0.82 for the MoCA. The latter correctly diagnosed 82% of the cognitively impaired and not-impaired HD gene mutation carriers and non-HD gene mutation carriers, whereas the MMSE only diagnosed 73% correctly.

Conclusions: The MMSE and the MoCA can both be used as cognitive screening tests in HD gene mutation carriers, but both have important limitations. Our results indicate that the MoCA is a better cognitive screening test for HD than the MMSE. In addition, our study provides estimated probabilities for cognitive impairment with different score ranges, which may be used as clinical guidelines in the interpretation of results from the two tests.