A Parent OT of a non-verbal level 2 child has put together a lot of work that hypothesizes autism is the impact of cells under stress due to genetics and then causing epigenetics to happen.

University of California San Diego School of Medicine has released a study that autism can arise from prolonged cellular stress response during critical developmental stage, similar to what Kimberly has discovered and put forward.

If it is, I would look at it the other way. These children that can be impacted by genetics causing stress need this stress & trauma release of crying and play to be optimal. This can be supported by the environment and caregiver education on childrens natural stress release and how to support their cry effectively. Unlike what is currently being taught by the psych industry of emotional supression. Whilst Autism is the genetics, the spectrum is the environmental impact and presentation of stress.

Early autoimmune challenges & inflammation could also be a source of stress impacting the development of this stress release system as its the same parts of the nervous system, like the vagus nerve. It's about getting a child out of any overload or reducing the source of inflammation e.g. food related or biological, making sure their cry is healthy or no other underlying conditions. Then meeting where the child is at developmentally with play and up-skilling from there. e.g. Attachment play starts at 2, before that peak a boo would be used instead of hide and seek. Contingent games with cause and effect around verbal sound and laughter could help non-verbal children. Some children have gestalt learning styles, one might have to identify that and then teach the play and developmental milestones again to support this stress release.

Fragile-x has reduced cognitive function, developmental milestones are harder and you have more frustration and stress to release, e.g. you would cry more as you struggle to figure out why you can't put the circle into the square hole. Understanding your caregiver to build the internal working model is harder. Learning the back and forth of play is harder. All these things cause this release to malfunction and invisible stress to build up.

The Highly Sensitive - Studies show that stressed Dad's sperm active epigenetics that increase sensitivity in their children. Either Parental stress and trauma gets passed on that increases nervous system sensitivity https://pmc.ncbi.nlm.nih.gov/articles/PMC7837765/. These children need to cry and release their bigger emotions meaning they have higher attachment needs and risk of this release malfunctioning and going into overload. Acquired autism is often this profile going into overload at 4 months old when sensory leaps causing more distress along with medical procedures like vaccines (not the vaccine content, just the need to cry more and the stress of the procedure) or 2-3 years old when testing the rules of the world causes too much stress as they go through the often delayed "terrible two's" along with the stress of separation at pre-schools/day cares.

Giftedness - Is similar too the highly sensitive. There is a high nervous system intensity that goes with the gifted profile means there is more emotions to release and a need to cry for longer, this hyper sensitivity is what can lead to the beautiful mind trope. Learning play can be hard from being at different developmental levels to peers all putting this stress release function at risk. People say IQ isn't from trauma but stress is what makes muscles grow, if you have the genetics for high IQ, it's the mapping of logic when building the internal working model of a failed attachment that works the brain increasing your empathy, logical and mapping of concepts abilities. The nervous system intensity is stress to the brain. Stress is what develops muscles and the brain. It impacts the development of networks as areas get over or under worked causing the 'spiky development' of twice exceptional children.

Incubator Babies - When left in an incubator or orphanage studies showed children's cry shuts down when left to cry it out with no one coming. This is why skin on skin is also seen as very important. This cry shutting down, separation trauma and other possible early medical traumas that fail to get resolved, puts the baby into overload impacting the parental attachment forming when they are finally out of an incubator. The more sensitive the babies nervous system the more at risk they are. This is why not all incubator babies end up autistic.

There are probably a million other sources and causes due to genetics and biology. e.g. As the nerves that do trauma do temperature, inflammation and autoimmune, they can all be sources of stress of this system and stress into the brain. When you suffer from inflammation you get headaches, vision and sound become more sensitive, this extra sensitivity can be enough to cause a child to go into an overload if it is prolonged over a period of time and could be possible sources.

ADHD could be someone with an higher nervous system energy with an impacted release that uses special interests to sooth their senses and learn but never went into overload (Often seen in gifted people who are known for higher intensity), impacting how they learn as brain networks develop. If they have gone into overload that would also be the AuADHD profile.

The impact of Hyper or Hypo sensitivity in the nervous system impacts what the insular cortex and supporting brain networks have to integrate and process influence presentations. If a brain is bombarded with sensory overload and has to build brain networks by processing this data, the faster the input the faster the brain learns to work like an athletes muscle being trained. The increase in empathy, the increase in logical reasoning or pattern mapping seen in the sensitive profile and gifted at the extreme end of the spectrum. Hypo sensitivity could cause a lack of stimulation impacting the growth and speed of these network.

Opposite to the above article, hypo nervous systems that have lower sensory input to the brain could lead to reduced cognitive function and impact development of neuro-networks and cause neurodiversity.