Cell and gene-based therapies for the lysosomal storage diseases

Lysosomal storage disorders (LSD) are a group of approximately 40 genetic diseases that are caused by the deficiency of one or more lysosomal enzymes. The incidence of LSD is estimated to be approximately I in 7500 live births, which makes this one of the more prevalent groups of genetic diseases in humans. The loss in enzymatic activity leads to the accumulation of undegraded substrates within lysosomes, resulting in distension of the organelle and subsequent cellular malfunction. Although palliative treatments such as enzyme replacement therapy (ERT) or substrate reduction therapy (SRT) have been shown to be effective for some of the LSD such as Gaucher, Fabry and MPS 1, they are not available as yet, or ineffective, for a large number of other LSD patients. To fulfill this unmet medical need, gene therapy is being considered as an alternate or adjunctive therapy for this group of disorders. A goal of gene therapy for LSD is to introduce a normal copy of the DNA for the lysosomal enzyme into a depot organ such as the liver or muscle with the intent that this will lead to the sustained production and reconstituion of therapeutic levels of the enzyme in the affected tissues. Here, we review the utility of various gene therapy strategies under consideration for the treatment of the LSD, including viral and non-viral gene transfer approaches, as well as stem cell transplantation.