Abstract
Cobalamin C is a rare inborn disorder of metabolism that results in multisystemic abnormalities, including progressive visual deficits. Although the cellular pathophysiology of cblC is a field of active study, little attention has been dedicated to documenting the cognitive consequences of the defect. The neuropsychological assessment of nine individuals aged between 23 months and 24 years was conducted to establish cognitive profiles. Results reveal a marked heterogeneity, with intellectual functioning ranging from extremely low to average, and cognitive difficulties (e.g., attention) evidenced even in those who are not intellectually disabled. Central nervous system abnormalities and multisystem disease are likely to be major contributing factors to the observed cognitive impairments, with the presence of visual deficits constituting an additional impediment to normal cognitive development. This study underscores the importance of conducting in-depth neuropsychological assessments in individuals with cblC, the results of which may be particularly helpful for clinical management, guidance toward rehabilitation services, and educational/vocational planning.