Expanding the cognitive spectrum of mitochondrial diseases.

BACKGROUND

Laboratory studies suggest a link between mitochondrial dysfunction and sociability. This study aimed to clarify the clinical significance of this hypothesis by evaluating theory of mind (ToM), a key precursor of social behaviour, in adult patients with mitochondrial disease (MD). The specific objectives were to clarify to what extent ToM may be impaired and whether may mark the cognitive profile of these patients.

METHODS

The Faux Pas Task (FPT), Attentive Matrices, Trail Making Test, Digit Span, Corsi Blocks Span, Short Story, and Rey Complex Figure Reproduction were used to assess ToM, shifting, memory, and praxis in MD patients and healthy controls.

RESULTS

Twenty-three patients and 23 controls were evaluated. The group comprised 12 patients with mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), all but one carrying the m.3243 A > G variant in MTTL1, seven with mtDNA macrodeletion and four with myoclonic epilepsy with ragged red fiber (MERRF) carrying the m.8344 A > G variant in MTTK. Compared to controls, the patients were significantly impaired in the recognition of real or non-existent mental states; the MELAS subgroup showed the most severe deficits. Attention and memory were impaired. Scores on the FPT (ToM factor) and other tests (no-ToM factor) predicted group membership, ranking 91% of patients and 78% of controls.

CONCLUSIONS

In adult patients with MD, particularly MELAS, ToM may be significantly impaired, which supports the clinical significance of the laboratory finding. Together with attention and memory deficits, ToM impairment may prove to be a cognitive marker of MD and provide an indication for therapeutic interventions.