G06 Genetic counselling for hd intermediate alleles: results of a survey looking at practice between genetics centres in the uk and beyond

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BackgroundAlthough intermediate alleles (27–35 CAG repeats) do not fall within the range to cause Huntington’s Disease (HD), they are susceptible to paternal germline instability, and so may expand into the reduced penetrance or full mutation range upon transmission to the next generation. The risk of IAs expanding into the HD disease causing range has been difficult to establish.Aims and methodsAt the EHDN conference in 2016, we presented two cases, where low risk intermediate alleles unexpectedly expanded into the full mutation range. Having discussed these cases locally, we had differing opinions whether to offer predictive testing to family members and whether prenatal testing or PGD would be offered.We recommended the need to develop a consensus guideline for the counselling of IAs between different genetic centres throughout the EHDN. In order to study this, we developed an online survey to determine practice between centres. This survey uses the two case examples we presented previously, to ascertain how different genetics health professionals would counsel each family regarding the risk of the IA expanding, and the implications for family members.Results and conclusionsTo date, we have received 25 survey responses from genetic counsellors, geneticists and HD researchers working in different centres worldwide. We present the results of this questionnaire which highlight the ongoing challenges associated with genetic counselling for IAs and the difference in practice between centres. The survey identifies a need for consensus guidelines, with over 60% of participants expressing a need for further guidance in this area.

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