Hi funnylegs4,
Is your friend an adult who didn't have these issues up until recently?

Bone density can be an issue with Vitamin D deficiency and that in turn can cause muscle and joint pain, cramps, fatigue, depression etc.. Some children who are on Autism spectrum are at risk of iron deficiency anaemia also.

I remember another post you wrote mentioning fatigue and I guess it's the same friend as you're talking about here? Both D deficiency and iron deficiency anaemia could make a person fatigued.

It is suspected that there is a link between D deficiency and autism in some people. You could find studies in PubMed if you type in the keywords.

If all these symptoms that your friend is experiencing are new and they haven't always had them then they certainly need to be checked out. It is a spectrum and no one person is going to have exactly the same comorbid conditions. More common comorbidities are conditions like epilepsy, tics, ocd or social anxiety. Things like that. However, that doesn't mean that everyone on the spectrum has them.

Ataxia is something that affects coordination and people with ataxia can have problems with their nerves and muscles. Some medications can cause ataxia as well.

Just curious, but has your friend had any type of illness prior to this all starting? A Strep throat for example or were they ever diagnosed with Rheumatic Fever when young?

Motor impairment would have showed up when young but from what you've said this sounds as if it's come on in adulthood, but I don't know how old your friend is now.

Well, that's just some ideas off the top of my head.
take care there.