Dalton Family Case Study Brett Dalton is 17 years old. He has just graduated from high school and is preparing to enter college soon. His family is preparing for relatives to visit for the Memorial Day weekend. Brett's mom, Lori Dalton, is very excited that all of her children will be home for the holiday weekend. Brett has a pair of twin sisters, Melissa and Mandy, who are both 21 years old, and both will be home. They have both just finished their third year of college. Brett's other sister, Sara, is 24, and she will be coming home with her husband Mark. Sara and Mark live in a town located about an hour away from the Dalton's home (where Sara grew up). Sara is a teacher in her town where she lives, and Mark works for a bank in the same town. They are excited to share their news about Sara's first pregnancy. She has been pregnant for eight weeks. The oldest of the Dalton siblings is Paul. He is 27 years old. He has a wife, Sally, and two kids (Andrew, who is 5 years old, and Allison, who is 3 years old). They live in a neighboring town, where Paul is a firefighter. Lori's husband, James Dalton, passed away three years ago from complications of Huntington's disease (which is caused by a dominant, autosomal mutation). Like James' father, John Dalton, James' symptoms declined from initial difficulty with coordination to finally requiring institutionalized care. James died at the age of 47. Both of James Dalton's parents (John and Connie) have also passed away; Connie did not have HD. James has only one sibling, a sister. Her name is Julie Ohman and she is 45 years old. She will be visiting the Daltons with her husband, Steve, and their son, Jeff. Like her older brother James, Julie also has HD. Her son Jeff just turned 18 and is now old enough to be tested for HD. He recently had the blood test for HD, and has received confirmation that he does not have HD. Melissa and Mandy are monozygotic (this means that one zygote formed; it split to give rise to two genetically identical embryos) twins, so genetically they are identical to one another. If one of them decides to get tested for HD, she will (as a result) receive results for both of them. Brett and his siblings have never been tested for HD. Brett is approaching the age of 18, the age at which he can choose to be tested for HD. How will the results of this test affect his decisions for the future? His four siblings can choose to be tested, but have not do so. Paul is approaching the age at which his father first started to show symptoms of HD. Sara is concerned that if she does have a copy of the mutation for HD, she would then have a 50% probability of passing that gene on to her unborn child.