A small breakthrough in hearing science has been made. The journal Nature Medicine has published a paper detailing how congenital deafness can be prevented by treatment early in development to correct gene expression.
Hearing impairment is the most common sensory problem and congenital hearing problems are present in around 1 in 1,000 newborns.
Hereditairy deafness is often caused by the cochlear hair cells either not developing properly or failing after birth.
In the research carried out by scientists from the Rosalind Franklin University of Medicine and Science, an antisense oligonucleotide (ASO) was used to correct defective pre-mRNA splicing of transcripts from the USH1C gene with the c.216G>A mutation. This is one of mutations which cause Ushers syndrome, a leading cause of deafness and blindness.
There are several different genetic mutations which result in Ushers syndrome. One causes deafness by failing to produce hormonin (a protein) which is needed for the tiny hairs which detect sound to grow.
The research involved making a small strip of genetic material which is attached to the genetic mutation, essentially repairing the mutated DNA to ensure that the body continues to produce hormonin.
The research was carried out on mice and it is hoped that the same process can provide a safe and effective treatment for humans too.
For the treatment to be effective it had to be given in the first 2 weeks of life. It is there vital that any child born with the condition is diagnosed immediately. Fortunately all maternity units in the UK carry out hearing tests at birth, along with many other health checks.
However, as the treatment needs to be given just after birth there may never be a cure for older children and adults.
It is certainly very encouraging that this condition can be treated at the early stages. Further research may well produce a more robust treatment in years to come, which could in theory eradicate deafness caused by Usher syndrome.
What is Usher Syndrome?
Usher Syndrome can cause hearing loss, reduce / failing vision and balance problems. Visual problems are caused by retinitis pigmentosa, which is a progressive condition where the retina degenerates slowly resulting in weaker signals being sent to the brain for visual processing.
Currently we are aware for 3 types of Usher Syndrome. Around 1 in 25,000 children born in the UK will have one of the conditions. It is autosomal recessive, meaning that a child will only have the condition if they receive a gene for it from both mother and father. Parents may carry one gene and therefore not have the condition, and be unaware that they carry the genetic mutation until they have their first child.
Usher Syndrome Type 1
A child born with this condition is usually completely deaf from birth, sign language being the only option for communication. Balance is often severely affected. Visual problems tend to start at around the age of 10 years. Reduction in night vision is the first sign of deteriorating sight. Complete blindness can result.
Usher Syndrome Type 2
A child will have moderate to severe hearing problems at birth, however, most children will be able to hear by using a combination of hearing aid and lip-reading. Sight problems are slower to develop ad may not start until they reach adulthood.
Usher Syndrome Type 3
At birth both hearing and sight are normal, but both will deteriorate later in childhood. The speed of deterioration varies though, some people will start to have problems in their teenage years. However, deterioration is severe, with total blindness and hearing loss being common by the age of 40 years.
What is Antisense Oligonucleotide ASO?
“A short strand of deoxyribonucleotide analogue that hybridizes with the complementary mRNA in a sequence-speciﬁc manner via Watson–Crick base pairing” Jasmine HP Chan, 2006.
Rescue of hearing and vestibular function by antisense oligonucleotides in a mouse model of human deafness by Jennifer J Lentz et al. Nature Medicine (2013) doi:10.1038/nm.3106 Published online 04 February 2013.
Usher syndrome – Sense.org.uk
Frontiers in Research Review: Cutting-Edge Molecular Approaches to Therapeutics:
ANTISENSE OLIGONUCLEOTIDES: FROM DESIGN TO
THERAPEUTIC APPLICATION (pdf) by Jasmine HP Chan, Shuhui Lim and WS Fred Wong. Clinical and Experimental Pharmacology and Physiology (2006) 33, 533–540