Editing Germline mutation (section)

=== Huntington's disease ===
[[Huntington's disease]] is an [[autosomal dominant]] mutation in the HTT gene. The disorder causes degradation in the brain, resulting in uncontrollable movements and behavior.<ref name=":14">{{cite web |title=Huntington disease |url=https://ghr.nlm.nih.gov/condition/huntington-disease |website=Genetics Home Reference |publisher=NIH |access-date=23 September 2018}}</ref> The mutation involves an expansion of repeats in the Huntington protein, causing it to increase in size. Patients who have more than 40 repeats will most likely be affected. The onset of the disease is determined by the amount of repeats present in the mutation; the greater the number of repeats, the earlier symptoms of the disease will appear.<ref name=":14" /><ref>{{Cite book|title=Huntington's Disease|last=Lawrence|first=David M.|publisher=Infobase Publishing|year=2009|isbn=9780791095867|location=New York|pages=92}}</ref> Because of the dominant nature of the mutation, only one mutated allele is needed for the disease to be in effect. This means that if one parent is affected, the child will have a 50% chance of inheriting the disease.<ref name=":15">{{cite web |title=Huntington's disease |url=https://www.mayoclinic.org/diseases-conditions/huntingtons-disease/symptoms-causes/syc-20356117 |website=Mayo Clinic |access-date=23 September 2018}}</ref> This disease does not have carriers because if a patient has one mutation, they will (most likely) be affected. The disease typically has a late onset, so many parents have children before they know they have the mutation. The HTT mutation can be detected through [[Genetic testing|genome screening]].