Sure, I'd be happy to share, but this is just an opinion.
Secure an appointment in a genetics clinic at a world-leading institution - think the sorts of hospitals that routinely see the rarest genetic diseases in the world, CHOP, CHLA, Rady in SD, Emory, Children's Boston, Lourie in Chicago (the children's hospital, not the cancer center), Nationwide in Columbus, Hopkins, etc. Ideally you'd be seeing someone who is continually identifying and publishing newly discovered genetic diseases.
Compose a short, concise document detailing developmental milestones as well as symptoms. Include all interventions that you have found to work and not work. Include all prior test and imaging results. This document will be given to the geneticist and genetic counselors you meet with. You can also look into having the medical record transferred over from the primary care facility to the geneticist's office.
Let them handle the rest. They may recommend testing, they may recommend consults with additional specialists, they may feel the issue is not genetic. It is important to keep in mind that one does not need to be far outside of the box to butt up against the limits of medical knowledge. It is possible that this strategy may not help. There are also research programs, such as the undiagnosed disease program at the NIH, that may also be potential avenues to pursue. It is also possible that the issue does not have an identifiable genetic cause, or if there is, the underlying pathology is currently not understood.
Good luck.