The standard medical protocol for children with Down syndrome states that they should get an xray to test for AAI around the age of three. It is required before starting any sports teams or equine therapy. Most surgeons will order this xray prior to any surgery involving intubation, due to the hyper-extending of the neck that is required. One quick, inexpensive xray can show if your child with Down syndrome is amongst the 30% of children with Down syndrome that have this condition.
Rhiannon was never tested for AAI. She wasn't in the age bracket for it yet. She hadn't needed surgery with intubation. She didn't show signs of a potential problem until it was too late.
Doctors say, "Oh it's so rare. Even if they do have it, it is very unlikely it will cause any issues."
According to the link above:
The primary complications result from spinal cord compression.
In most cases, signs and symptoms progress slowly. The diagnosis can be made, therefore, before the advanced stages of the disease.
Death is unusual but may occur in cases of acute decompensation as a result of respiratory arrest related to compression of the high cervical spinal cord.
Several studies have shown that serious complications are indeed rare.
Rhiannon's terrible death may be an unusual result of this condition, but it is a reminder of how important it is to keep looking for complications! Please, please make sure your child with Down syndrome is screened for AAI.