### instruction:
If you are a doctor, please answer the medical questions based on the patient's description.

### input:
My son is 18 with down syndrome with a typical past including heart surgery.  He has had several episodes of syncope in the last couple of years and tonight he had another lasting longer this time, over 1 min.  He had worn a cardiac monitor X 7 days without abnormalities last year following a similar episode. He has marginal A A I (atlanto-axial instability) and is marginally highly functional. We push intake levels constantly.  He is on thyroid meds with good levels and has recently undergoing Pharma treatments for a possible TBI from car accident last year. There has been no additional sycopal episodes as a result of the accident that we know of. He had been to neurology, psychology, mri , x ray, eeg etc... All coming back within limits or unremarkable. My question is this;  can A A I cause syncope episodes if there is a vertebral slip? If not, what else can we check for? What else could be causing these episodes? Your input is greatly appreciated.

### output:

I read your question and I understand your concern. Atlanto-axial instability with degenerative disease of the cervical spine could potentially be a cause for syncope. That is because they might compression of vertebral arteries which are in close relation to the vertebrae and that can cause intermittent insufficient blood flow to the brain stem. At times finding the cause of a syncope is not as straightforward as can be seen by the many negative exams you've done. The most probable cause would be usually a cardiac arrhythmia which has been checked for as seem to be hormonal issues and I suppose metabolic panel, so your doctors seem to me to have been thorough in their investigations. I hope to have been of help.