Gene therapy approaches to replace a faulty gene with a healthy gene have been proposed and are being studied for treating some genetic diseases. As of 2017, 11.1% of gene therapy clinical trials targeted monogenic diseases.
Diseases such as sickle cell disease that are caused by autosomal recessive disorders for which a person's normal phenotype or cell function may be restored in cells that have the disease by a normal copy of the gene that is mutated, may be a good candidate for gene therapy treatment. The risks and benefits related to gene therapy for sickle cell disease are not known.
Gene therapy has been used in the eye. The eye is especially suitable for adeno-associated virus vectors. Luxturna is an approved gene therapy to treat Leber's hereditary optic neuropathy. Glybera, a treatment for pancreatitis caused by a genetic condition, and Zolgensma for the treatment of spinal muscular atrophy both use an adeno-associated virus vector.