Prof Maria Bitner - childhood deafness

Kat - You're listening to the Naked Genetics podcast with me, Dr Kat Arney. Now it's time to delve into some of the issues around the genetics of childhood deafness with Professor Maria Bitner-Glindzicz (glinjich) from UCL's Insitute of Child Health. I started by asking her where we are at the moment with hunting down genetic causes of hearing loss in childhood.

Maria -  We can only look for really the most common genetic forms of hearing loss in childhood.  So, these are one or two, maybe three or four genes that are commonly mutated in childhood onset hearing loss or genes which give rise to a distinctive clinical picture which we can pick out and identify clinically as belonging to a subset of genetic causes.

Kat -  Now obviously, it's only useful to identify something if you can actually then do something about it.  It's not very useful to say to a child, "You've got this gene problem, sorry."  What can we now do with that knowledge, knowing that a child has a particular gene fault?

Maria -  In terms of treatment, treatment is still very limited, but the kinds of benefits that might come out of having a molecular cause are that you might know that one particular type of deafness is associated without the medical problems.  In which case, that knowledge will be useful because having made the diagnosis, you would then go and look for the other medical problems and put in place maybe treatments or screening for that.  I'm thinking of syndromes so, syndromic causes of deafness.  Actually, treating the deafness itself is more difficult, but if you knew that a particular type of deafness was likely to progress or get worse, then again, you might be more likely to refer the child on for something like a cochlear implant assessment.  So, in that respect, there are some benefits to be gained.  The other benefits really are in terms of genetic counselling, so it might not be very interesting for the child themselves to know their cause of deafness.  But for the parents, it might very important.  If they're thinking of having more children then knowledge that their child's deafness is genetic or that it is or is not associated with other medical problem might have a major influence on whether or not they decide to have more children.

Kat -  What sort of syndromes and types of hearing loss are we talking about with these genes that we do know about?

Maria -  Well, some of them involve major clinical problems and these are just minor clinical features that just help you to make a diagnosis.  So, one of perhaps the major syndromes would be something like Usher Syndrome where congenital hearing loss is associated with later onset, by which I mean teenage onset, for retinal degeneration that ultimately leads to blindness.  So, that's clearly a very disabling condition and an important diagnosis to make for the reasons that I've just outlined.  Other syndromic forms of deafness, maybe we don't have major clinical complications - so, something like Waardenburg syndrome includes the association of deafness but with unusual pigmentation of the hair or skin or eyes.  That doesn't cause the person any medical problems, but it helps us to identify the cause, how it's inherited, and maybe to some extent, what the future will hold for that person.

Kat -  Where do you see us going in maybe 5 to 10 years with moving from the knowledge gained in the lab, from the animal research and the big genetic studies that are tracking down these genes?  Where would you like to see that heading in terms of how we can improve the outcomes for patients?

Maria -  I think there will be much better diagnosis.  So, the proportion of children and families in whom you can actually say, "Well, this is the cause", I think that's going to take another leap forward.  I think, what we know about the time course of some forms of deafness I think is really also going to improve, because at the moment, although we know a number of genes that can cause hearing loss in humans, our clinical knowledge based on a handful of cases.  So, once that handful then becomes hundreds of cases you get a much better idea of what that type of deafness involve, or will looks like, and what will happen over time.  I think we will be able to - as a result of that - maybe predict better which children will get more benefit from cochlear implants.  So, some children appear to do very well after cochlear implants and some do far less well.  There might be lots of factors for that, but one of those factors might be the cause of their hearing loss.  If you could subdivide what's at the moment a very mixed group of children into different groups and then follow them up, I think that will be very useful.  And of course, I suppose ultimately, one aim is to prevent progressive deafness and maybe to treat some forms of deafness.  I think once we understand better about why people are deaf then we can begin to tackle those much more difficult aims.

Kat -  Slightly changing tack, one of the other interests of your research group is studying how hearing can be damaged through things like drugs and the genetic link to that.  Can you explain a bit more about what's going on there?

Maria -  Yes.  We are interested in a particular type of hearing loss which, essentially, is a genetic predisposition to hearing loss after a group of antibiotics called aminoglycosides.  So, if you have this predisposition and you have these antibiotics, you can experience a really rapid deterioration in your hearing which is irreversible.  Of course, that begs the question of, "If you know who these people are, then surely, you just don't give them these antibiotics."  Of course, that's the obvious thing, but one has to try and work out how they cause this type of hearing loss and the best way of trying to pick up people who are sensitive.

Kat -  It does seem that more and more, we are understanding how our genetics make us almost unique in how we respond to the drugs and treatments that are available.  Do you think this is going to be an increasingly important field in the future?

Maria -  I think it has to be.  I think all of those drug reactions that one learns about as a medical student and junior doctor, you're beginning to realise now that these are probably all genetically based.  They are likely all to be explained by the genetic makeup of a person within the next decade.  To me, that's really fascinating - all of these rare idiosyncratic drug reactions are likely to be genetic.

Kat -  What first got you interested in studying deafness and hearing loss?

Maria -  That's a very good question and, as many people do, I think you come to it in a rather roundabout way.  I was very fortunate when I came here to the Institute Of Child Health as a young geneticist that an interest in genetic hearing loss had already been established by some of the researchers who preceded me.  So, it was very easy to see that it was going to be a field that was opening up.  

We had an excellent team of paediatric audiological physicians who'd built the department here really from nothing.  We were one of the first centres to do paediatric cochlear implantation.  We had a fantastic clinical genetics department, and it was realised that actually, genetic hearing impairment was an area that had been really neglected in terms of clinical studies.  So, it was an ideal field to enter really.  Of course, as soon as you enter into a clinical or a research field, you meet other people who inspire you, you meet patients that you remember or whose stories somehow touch you really and spur you on to try and find out more.

Kat - That was Professor Maria Bitner-Glindzizc from UCL.