Patients with Uner Tan syndrome (UTS) exhibit habitual quadrupedal locomotion (QL), intellectual disability, dysarthric speech and truncal ataxia. Examination of cognitive ability in this syndrome has not yet been demonstrated in the scientific literature. Aims: (i) To analyze the cognitive abilities of the siblings with UTS; (ii) to assess the grade of their ataxia in relation to cerebellar disorders; (iii) to measure the metabolic activities of various cerebral regions in comparison with healthy individuals; (iv) to detect the interrelationships among all of the measured variables (IQ test scores, ataxia scores, cerebro-cerebellar areas and their metabolic activity levels) to reveal the holistic activity of the brain. The Minimental State Examination (MMSE) and Wechsler Adult Intelligence Scale (WAIS-R) were applied to the affected cases and healthy subjects. Cerebellar disorders were assessed by the International Cooperative Ataxia Rating Scale (ICARS). Brain MRI scans were performed and cerebro-cerebellar areas were measured on MRI scans, including their metabolic activities (SUV), measured by positron emission tomography (PET) scanning. MMSE and WAIS-R scores both correlated with cerebro-cerebellar areas. Cerebello-vermial areas and their metabolic activities were significantly smaller in patients than in normal controls; areas of the remaining structures were not significantly different between patients and healthy subjects. Brain areas significantly inter-correlated: ICARS negatively correlated with WAIS-R, MMSE scores, SUV, and cerebro-cerebellar areas, which significantly correlated with each other. The results suggested (i) ICARS may not only be a test for cerebellar disorders, but also may be related to global functioning of all of the cerebro-cerebellar regions; (ii) ICARS, WAIS-R and MMSE may be measures of emergent properties of the holistic activity of the brain; (iii) the psychomotor disorders in UTS may be related to decreased brain metabolism.