What makes a disease a good candidate for gene therapy

Diseases that are best candidates
for gene therapy are those whose disorder has been identified to be a malfunctioning
gene and the biology of the gene is well known.  Gene therapy
is also viable
where the proper gene can be correctly delivered and replace the malfunctioned one.

The advantage of using viruses
in gene theory is their effectiveness in
delivering the desired gene by tapping into their natural mechanisms of
infection.  However, disadvantages include the risks of affecting
healthy cells while targeting sick cells and wrong placement of the desired gene hence causing undesirable mutations
in DNA.

One factor is the length
of the DNA that is required to be
replaced through gene therapy. Most vectors have a maximum length of DNA that they
can carry for effective transduction.  Another
is the range of cell types that the vector can infect and the risk of immune response/
allergic reaction/ side effects.

The best vectors are herpes or vaccinia viruses.  The viruses are able to infect non-dividing cells such as the nerve cell. The vectors can accommodate 8400 bp in their genome
and the transgene expressions have the potential
to last long.

Traditional gene editing techniques
such as TALENS and ZFN use modular proteins that target nucleotide sequences. In
the CRISPR tool, the Cas9 protein is steered by a guide RNA (which is a complementary
sequence to the target sequence) to the target region.

One ethical issue of gene
editing is its use in genetic enhancement to develop ‘designer babies’.  The question of who should decide on whether a
trait is bad or good also complicates this matter. The morality of artificiality
enhancing attributes such as strength, athletic capability, intelligence, and etcetera
could lead to an unhealthy ‘arms race’  between
humans.

In sports doping, gene editing
could be used to enhance genes that enhance muscle strength by targeting
myostatin (MSTN) and GF-1 genes. Genes that promote quick break down of lactic
acid and increases oxygen capacity of the lungs and blood such as EPO gene could
be targets of sports doping.

Gene editing will treat
diseases and disorders by repairing the causative defective gene. This is already
applicable in cystic fibrosis. Artificial gene selection will be common in
future thanks to gene editing.  Future
humans will, therefore, have ‘desirable traits’  or new traits depending on what is appealing to
the society.