A lot of inherited diseases or disorders are caused by variations in individuals’ genomes; from a single nucleotide mutation to a whole chromosome being missing. For example, colour blindness occurs following a point mutation on the X chromosome, Down’s syndrome is due to the presence of an extra chromosome n*21 and Duchenne muscular dystrophy is caused by a deletion of a gene on the X chromosome.
If you know which genes and which alleles both parents have, you can determine the probability of a child receiving each allele. Say for example, the mother suffered from haemophilia, caused by a point mutation on the X chromosome, her male children would also have the condition, since they would inherit their X chromosome from the mother.
Now imagine a world in which genetic disorders can be prevented. A world in which some lethal genetic associations can be fixed, and where diseases such as sickle-cell disease are no longer an issue. Despite sounding like something straight out of a Sci-Fi movie, genetic engineering is becoming more and more useable, all thanks to a method called CRIPSR.
Clustered Regularly Interspaced Short Palindromic Repeats, or CRISPR for short, is an immune system found in bacteria, which they use to fight against foreign DNA. With the CRISPR/Cas system, prokaryotes are able to acquire a form of resistance to things such as plasmids or phages, by removing the exogenous DNA from their own.
This system has been used and exploited by scientists to edit genomes. First used to create gene knockout models, CRISPR can now be used to activate or repress target genes, purify specific sections of DNA and even image DNA in live cells using fluorescence microscopy, all of which can have a huge impact in the medical field. It can be used to genetically engineer embryos before their implantation, in order to ‘fix’ disease-causing mutations.
Recently, a team based in the USA have successfully cured an embryo of a disease known as hypertrophic cardiomyopathy (read the paper here). This disease, mostly caused by a mutation in the MYBPC3 gene, has a high prevalence in adults, and manifests clinically with heart failure. The team, led by Hong Ma, used the CRISPR-Cas9 system to fix implanted embryos that had the mutation. The embryos engineered in this study were not implanted, and the researchers recognise that more work needs to be done in order to optimise this gene editing approach before it can be used clinically.
Despite having huge potential for curing and preventing disease, people are unsure whether gene editing is ethical. It is thought that if doctors were able to genetically modify embryos to prevent diseases, they could also genetically modify them to ensure the gender, hair colour etc. of the future child. This could lead to people giving birth to “designer babies” which poses a huge ethical question. Furthermore, this could lead to scenes as in movies such as Gattaca (1997), where people are judged according to their gene make up rather than who they are.