Hi. Gosh, I feel for you. Medical mysteries involving our kids is not fun. I have a son with sensory integration disorder. Lots of kids with autism also have this although my son wasn't diagnosed as autistic. He meets the criteria for autism I take it but has these overlapping conditions? I think that I'd personally continue to have him evaluated and treated for the eye issue and the other one you are concerned about while still working diligently with intervention for autistic symptoms. Here is a bit of a simplistic article on things that look like autism but aren't. https://www.webmd.com/brain/autism/autism-similar-conditions#1 You can look into 22q11.2 deletion syndrome as suggested as that is something that mimic's autism and is genetic and the suggestion to look into lead poisoning is sound as well.
What types of intervention do you do? My son is now a teenager. He had a very difficult time early on. We were told he'd never attend school without an aid. He does. He has straight A's in honor classes, participates in sports and band and has a few good friends. Intervention was absolutely key. Small steps. And whatever he worked on in therapy, we reinforced all week at home. I became his personal therapist and I also have a son a year younger than him that got to do all of the same things with him. We made it into a lot of games and as fun as possible. To this day, my son battles a lot of GI issues, processes slowly, and has social skills issues. His fine motor is that of a 9 year old even though he is 15. But we emphasize the positives and overall, he is doing very well. So, I highly recommend intervention, therapy, and focusing on the positives in life. Let me know if you need to talk!
And btw, there is also this, which may or may not be relevant:
Mitochondrial Citrate Transporter-dependent Metabolic Signature in the 22q11.2 Deletion Syndrome
"Nine of ∼30 genes involved in 22qDS have the potential of disrupting mitochondrial metabolism... Metabolite differences between 22qDS children and controls reflected a shift from oxidative phosphorylation to glycolysis..."
Ocular findings associated with chromosome 22q11.2 duplication.
"Because of the high incidence of conditions that could affect visual development, we recommend that children with 22q11.2 duplication syndrome have a complete ophthalmological examination..."
In that study, 1 out of 19 had nystagmus, which happened to resolve spontaneously.
So that seems like it's worth a look, Rachanne.
There's also lead poisoning. Please let me know what you think, and also whatever might develop from these possibilities. Good luck.
"is there any diseases that mimic autism and also cause the nystagmus that I should request testing for"
Some quotes from that page:
There are a variety of physical and behavioral disorders that have been linked to 22q11.2 deletion syndrome. The syndrome has the potential to impact every system in the body and can therefore lead to a wide-range of health issues.
The majority of these patients also have congenital heart defects
Gastrointestinal problems, including constipation, and GERD
Growth problems, sometimes associated with growth hormone deficiency
Developmental delays, including both language and motor skills delays