Markers of cognitive function in individuals with metabolic disease: Morquio Syndrome and Tyrosinemia Type III

We characterise cognitive function in two neurodegenerative metabolic diseases where cognitive effects have been considered mild or non-existent. We asked whether cognitive effects were present and whether the cognitive effects of neurodegeneration were hetero- or homogeneous across diseases. Thirteen Morquio syndrome patients, 11 Tyrosinemia Type III patients and 104 controls were assessed using tasks for attention (simple RT, feature and conjunction visual search), language (BPVS, BNT) and oculomotor function (fixation, pro-saccade, anti-saccade, smooth pursuit). There were different patterns of deficits. In Morquio syndrome, visual search was slow, differences did not increase in proportion to display sizes and were not driven by the longest reaction times in the distirbution. In addition, maintaining gaze on a target in an oculomotor task was difficult. These patterns point to problems with control processes for attention. Language was relatively spared. In Tyrosinemia Type III, in contrast, there were modest effects in attention, but language was clearly affected, and effects increased with age. Both diseases presented clear evidence of cognitive effects, but with different functional profiles. The different markers (attentional control in Morquio and language in Tyrosinemia) are good candidates for disease tracking and for establishing functional/biological links and they suggest that there may be stronger impacts in different regions of the brain (frontal vs temporal areas).