What is genetic testing for inherited retinal disease?
In Ophthalmology (which a scientific journal for eyes) this year and month, 2017 July, there was an excellent article on gene testing for inherited retinal disease (IRD) by Professor Anthony Moore who worked at the Institute of Ophthalmology and whose job Professor Michel Michaelides has now taken over.
Professor Moore writes about the revolution underway in molecular genetic testing for inherited retinal disease (IRD). IRD includes many conditions including retinitis pigmentosa, Stargardt’s disease, Usher’s syndrome, achromatopsia, cone dystrophies, etc. These diseases affect young adults and adults of working age. They are the largest cause of blindness in young people in the Western world.
He explains how a new approach is using next generation sequencing (NGS) which is a term used to describe some different technologies that use a strategy of parallel sequencing of absolutely millions of short segments of DNA that are then aligned bioinformatically to the human reference genome. To have a good accuracy of sequencing, each fragment is sequenced multiple times.
Next generation sequencing (NGS) is used to completely sequence an individual’s DNA, known as whole genome sequencing, including sequencing the protein codeine regions, known as Exome sequencing, or can combine the sequencing to coding regions of panels of genes known to cause specific disorders in inherited retinal disease.
This technology has advanced to the stage that whole Exome sequencing and whole genome sequencing can be performed in a short timeframe and the cost of the tests continues to decrease. Next generation sequencing test panels of all known retinal disease genes are already in clinical use, and whole genome sequencing is further increasing the diagnostic yield.
Professor Moore went on to write about how inherited retinal dystrophies affects approximately 1 in 3,500 individuals in North America and Europe and are an important cause of blindness in children and adults of working age. Most affected individuals do not get to see a specialist in IRD such as Professor Michaelides, at least initially, and the diagnosis of inherited retinal disease (IRD) is likely to be made by a general ophthalmologist, paediatric ophthalmologist or retinal specialist.
Some questions arise. Who should have genetic testing and what difference do the results of molecular genetic testing make to clinical management and who will pay for the testing?
Molecular genetic testing provides a very specific diagnosis, which certainly will help genetic counselling for the patients and their wider family members. For instance, approximately 50% of patient with retinitis pigmentosa have no known family history, and although most will have an autosomal recessive disease, some will represent a new autosomal dominant mutation or have an X-linked disease.