Genetic technology applied to medicine — practice question

One cause of the genetic disease severe combined immunodeficiency (SCID) is a mutation in the $ADA$ gene. As a result, the enzyme adenosine deaminase (ADA) is not produced in sufficient amounts. ADA is present throughout the body, but its activity is especially high in lymphocytes. When functional ADA is absent, toxic metabolites accumulate, which destroys lymphocytes and harms organs. Babies are usually diagnosed with SCID by six months old. With treatment, the life expectancy of children with SCID can be improved greatly. Several treatment choices exist. • Enzyme replacement therapy using recombinant human ADA produced by genetically modified (GM) $Escherichia\ coli$. The treatment is given as weekly intra-muscular injections. • Bone marrow transplant, provided a suitably matched donor, such as a close relative, is available. • Gene therapy.