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<p>Not all medical procedures that introduce alterations to a patient&#39;s genetic makeup can be considered gene therapy.&nbsp;<a href="https://en.wikipedia.org/wiki/Bone_marrow_transplantation" title="Bone marrow transplantation">Bone marrow transplantation</a>&nbsp;and&nbsp;<a href="https://en.wikipedia.org/wiki/Organ_transplants" title="Organ transplants">organ transplants</a>&nbsp;in general have been found to introduce foreign DNA into patients.^{<a href="https://en.wikipedia.org/wiki/Gene_therapy#cite_note-5">[5]</a>}&nbsp;Gene therapy is defined by the precision of the procedure and the intention of direct therapeutic effect.</p>

<p>Following early advances in&nbsp;<a href="https://en.wikipedia.org/wiki/Genetic_engineering" title="Genetic engineering">genetic engineering</a>&nbsp;of bacteria, cells, and small animals, scientists started considering how to apply it to medicine. Two main approaches were considered &ndash; replacing or disrupting defective genes.^{<a href="https://en.wikipedia.org/wiki/Gene_therapy#cite_note-28">[28]</a>}&nbsp;Scientists focused on diseases caused by single-gene defects, such as&nbsp;<a href="https://en.wikipedia.org/wiki/Cystic_fibrosis" title="Cystic fibrosis">cystic fibrosis</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Haemophilia" title="">haemophilia</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Muscular_dystrophy" title="Muscular dystrophy">muscular dystrophy</a>,&nbsp;<a href="https://en.wikipedia.org/wiki/Thalassemia" title="Thalassemia">thalassemia</a>, and&nbsp;<a href="https://en.wikipedia.org/wiki/Sickle_cell_anemia" title="Sickle cell anemia">sickle cell anemia</a>.&nbsp;<a href="https://en.wikipedia.org/wiki/Glybera" title="Glybera">Glybera</a>&nbsp;treats one such disease, caused by a defect in&nbsp;<a href="https://en.wikipedia.org/wiki/Lipoprotein_lipase" title="Lipoprotein lipase">lipoprotein lipase</a>.^{<a href="https://en.wikipedia.org/wiki/Gene_therapy#cite_note-Gallagher-27">[27]</a>}</p>