Most rare diseases currently lack a satisfactory therapeutic alternative. Many of these diseases affect children who either do not survive the disease or do so with severe sequelae. The important advances achieved in recent times in terms of technological development of vectors and knowledge of the molecular mechanisms involved in the development of the disease invite optimism and allow us to venture that in the coming years gene therapy could become the treatment of choice for these diseases. In fact, the first gene therapy treatment has already reached the market in the western world. The drug is an adeno-associated virus for the treatment of a rare disease, lipoprotein lipase deficiency, which will initially be administered to patients with recurrent pancreatitis17. Hopefully this is only the first in a long line of new treatments for rare diseases based on gene transfer.