There is a considerable interest in developing gene therapy for neurogenetic disorders because the conventional treatment is inadequate and unsatisfactory. Diseases most amenable to gene therapy would be those where a single gene product is missing and the gene expression has a simple mechanism, particularly several hereditary metabolic disorders involving the nervous system. The aim of somatic gene therapy in neurogenetic disorders is to replace the missing enzyme and improve the clinical symptoms. Gene therapy cannot eradicate the disease or prevent its transmission to offspring; this can be achieved only by germline gene therapy, but it is currently not permitted on ethical grounds.
• By changing the pathophysiological concepts and classification of several diseases, molecular diagnostics may pave the way for gene therapy of neurogenetic diseases.
• Identification and replacement of defective genes in monogenic genetic disorders are ideal therapies, but they are not essential.
• Gene therapy has been shown to be effective in laboratory models of disease, but the long-term efficacy in human patients remains to be demonstrated.
Historical note and terminology
Gene therapy can be broadly defined as the transfer of defined genetic material to specific target cells of a patient for the ultimate purpose of preventing or altering a particular disease state. Carriers or delivery vehicles for therapeutic genetic material are called “vectors”; these vectors are usually viral, but several nonviral techniques are being used as well. The history and basics of gene therapy are described in the introductory article on gene therapy.
Gene therapy usually implies the introduction of altered genes into the body of a patient instead of just the products of cells with altered genes. The term "genetic engineering" applies to genetic manipulation of living cells and implantation of genetically engineered cells into the living body and can be considered as a form of gene therapy. Neurosurgeons refer to gene therapy as "cellular and molecular" neurosurgery.
Application of gene therapy to neurogenetic disorders will be described here. This will include inherited disorders of metabolism as well. Gene therapy of Duchenne muscular dystrophy is the topic of a separate MedLink article. With few exceptions, no rational therapies exist for any of these diseases. Molecular diagnostics have changed the pathophysiological concepts and classification of several neurologic disorders and may pave the way for gene therapy of several presently incurable neurologic diseases.
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