Abstract: Provided are compositions and methods for treating progressive neurological childhood symptoms and conditions associated with lysosomal storage disorders (LSD) such as neurological mucopolysaccharidoses. The compositions may include nootropic peptides such as Semax, which can be N-terminally acetylated and/or C-terminally amidated. The peptides can be effectively delivered by intranasal administration into the brain parenchyma, where they exert a neuroprotective and anti-inflammatory effect and delay or restore neuropathophysiological defects such as neuropsychiatric problems, developmental delays, mental retardation and dementia.