Genetic disease, and gene therapy

Although simple in concept, the application of gene therapy to treat/cure genetic diseases has, thus far, made little impact in practice. The slow progress in this regard is likely due to a number of factors. These include  

Low-density protein receptor Adenosine deaminase Purine nucleoside phosphorylase Sphingomylinase Glucocerebrosidase 

CH14 NUCLEIC-ACID- AND CELL-BASED THERAPEUTICS 

Another early genetic disease for correction by gene therapy was SCID. One form of this disease is caused by a lack of adenosine deaminase (ADA) activity. ADA is an enzyme that plays a central role in the degradation of purine nucleosides (it catalyses the removal of ammonia from adenosine, forming inosine, which, in turn, is usually eventually converted to uric acid). This leads to T- and B-lymphocyte dysfunction. Lack of an effective immune system means that SCID sufferers must be kept in an essentially sterile environment. 

When compared with treating diseases such as thalassaemia, regulation of the level of expression of a corrected ADA gene was believed to be less important for a successful therapeutic outcome. (In most, though not all, metabolic diseases caused by an enzyme deficiency, it appears that expression of even a fraction of normal enzyme levels is sufficient to ameliorate the disease symptoms.) 

Severe combined immunodeficiency Adenosine deaminase, purine nucleoside phosphorylase 

Cystic fibrosis Cystic fibrosis transmembrane regulator 

Maple syrup disease Branched chain a-ketoacid dehydrogenase 

Glycogen storage deficiency type 1A Glucose-6-phosphatase 

---