Fumarase deficiency, psychomotor retardation, succinylaminoimidazole carboxamide riboside, succinyladenosine, succinylpurines, cerebrospinal fluid.The report described presence of succinylaminoimidazole carboxamide riboside (SAICAR)in the cerebrospinal fluid of a patient with deficiency of fumarase.The neurotoxic metabolite increase is caused by secondary inhibition of adenylosuccinate lyase by accumulating fumarate and its presence may be seen as a casuse of neurological impairment.