How can someone be born double jointed ?

Question: How can someone be born double jointed ?
- Keywords:
  body,
  double jointed
Asked by 759heah26 to Bobby, Claire B, Claire C, David, Veasna on 15 Mar 2017.
- Veasna Sum-Coffey answered on 15 Mar 2017:
  
  Great question! Being double jointed is genetic because of the muscles that allow you to outstretch your fingers or other limbs. The genes that allow these muscles to hyper-stretch can be passed on to future generations.
  
  I can stretch my thumb to my wrist, and so can my daughter! 🙂

Question: How can someone be born double jointed ?