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How genetic counselling works in practice

The stories of two families with different backgrounds and questions.

Family 1 – Bronwen and James Dad and son
Bronwen and James are both hearing. They have one son, Callum, who has no hearing loss and is now at preschool. They are very surprised when their second son, Sam, has no clear response on his newborn hearing screening test and follow up tests show that he has severe deafness. There is no-one else in the extended family who is known to have been deaf. There are other appointments to have with paediatricians, audiologists and Teachers of the Deaf over the next few months, but when Sam is three years old, they decide that they would like to find out more about the cause of his deafness.

Their paediatrician checks through Bronwen’s medical history during pregnancy and they cannot think of any infections or problems during birth that could have affected Sam’s hearing. She checks a urine sample for blood or protein, does some blood tests to look for infections, refers Sam for an ECG (a recording of the rhythm and electrical activity of the heart) and a scan of the structure of his inner ear (CT or MRI scan) and arranges for James, Bronwen and Callum to have their hearing checked formally. She has already arranged for Sam to have his vision checked in the past. None of these tests pick anything up. She then refers them to see a clinical geneticist and a genetic counsellor. The genetic counsellor talks to them on the phone before the appointment and takes a family history as far back as James and Bronwen’s brothers and sisters and parents. She also explains what to expect at the appointment.

In the clinic, the clinical geneticist reviews with them all the tests Sam has had already and offers to arrange for the Connexin 26 gene to be tested for alterations. James and Bronwen say yes to this so some local anaesthetic cream is put on Sam’s arm to numb the area and then a small blood sample is taken. This test takes about four months to be completed and the clinical geneticist arranges to see James and Bronwen with the results. It has picked up alterations in both copies of Sam’s Connexin 26 gene and the alterations are ones that have been seen in many children with deafness in the past. The clinical geneticist explains that this is the cause of Sam’s deafness and they go on to discuss how this is inherited in a recessive way. This means that, if James and Bronwen decide to have another child, there will be a 1 in 4 chance that the child will have hearing loss. The level of hearing loss could be the same as Sam’s or more or less and this could not be predicted. In the future, the chance for Sam of having a child with deafness is likely to be less because his partner would also have to carry an altered Connexin 26 gene. It is suggested that he could ask more about this in his own right when he is an adult. The genetics professionals encourage James and Bronwen to contact them if they have further questions or if they want a follow-up appointment.

Family 2 – Ahmed and Ruby
Ahmed and Ruby have both been profoundly deaf from birth and Australian Sign Language (Auslan) is their preferred language. Ruby is the only deaf person in her family and her mother thinks that she came into contact with a friend with german measles (rubella) during the pregnancy though she did not have any symptoms herself. Ahmed’s parents are deaf from birth as well and, on his mother’s side, both his grandmother and great-grandfather were also deaf. Ahmed and Ruby are thinking about starting a family and are interested to know whether they are likely to have deaf or hearing children. Their GP refers them for genetic counselling. The genetic counsellor notices that Ahmed is going quite grey although he is only 23. He asks about other people in the family who have gone grey early and Ahmed says that his mother has had a distinctive white patch at the front of her hair for as long as he can remember. He also remembers that his grandmother had one brown eye and one blue eye.

When they come to the clinic, again with the interpreter, the clinical geneticist explains that the pattern of deafness, white patches or early greying in the hair and different coloured eyes can fit together in Waardenburg syndrome and she thinks that Ahmed probably has this. Ahmed and Ruby have heard of this in the past.

Nothing is picked up with any of the other tests. This means that it is not possible to say what the cause of Ruby’s deafness is. It might have been the contact with rubella during her mother’s pregnancy, but this cannot be proved. It is possible to say more about Ahmed’s deafness. As all his other tests have come back without picking anything up, it looks highly likely that the initial suggestion is correct and that he has Waardenburg syndrome. This is inherited in a dominant way and this means that there is an equal 1 in 2 (50%) chance each time they have a pregnancy that the altered copy will be passed on. However, the clinical geneticist explains that not everyone who has Waardenburg syndrome has all the features: a person might have deafness, but they might not. This means that the chance of a child being born with deafness is less than 1 in 2. Ahmed, Ruby and the genetic professionals decide that they do not need to make another follow-up appointment at this stage, but Ahmed and Ruby can get back in contact if they have more questions.

Information provided by the National Deaf Children's Society. Reproduced with permission.

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04-Aug-2022 2:58 PM (AEST)