The present invention relates to Adeno-associated virus type 9 methods and materials useful for intrathecal delivery of polynucleotides. Use of the methods and materials is indicated, for example, for treatment of lower motor neuron diseases such as SMA and ALS as well as Pompe disease and lysosomal storage disorders. It is disclosed that administration of a non-ionic, low-osmolar contrast agent, together with a rAAV9 vector for the expression of Survival Motor Neuron protein, improves the survival of SMN mutant mice as compared to the administration of the expression vector alone.