Oh me either don't worry - CS with a personal interest in genetics/RCCX.
At a (quick) skim, RCCX can set the terrain for Frye’s “cerebral folate disorder” pattern. The block on 6p21 carries C4A/C4B for complement, CYP21A2 for steroid 21-hydroxylase, and TNXB for tenascin-X, with tight linkage and lots of copy-number shuffling.
How this maps to the folate-receptor autoantibody story and folinic response:
- C4 structure and dosage can raise baseline autoantibody risk. Higher autoantibody risk makes FRAA more likely.
- TNXB variants can track with hypermobility, dysautonomia, and GI dysmotility. Weaker barriers and altered motility increase exposure to food and microbe antigens, which raises chances of receptor-directed autoimmunity like FRAA.
- CYP21A2 alleles can shift cortisol and androgen tone. Stress-hormone tone sets immune thresholds and brain energy demand, which makes folate transport failure hit harder.
- Put together, you get a terrain with more autoimmunity, more redox strain, and more antigen exposure. That combo can yield low CSF folate with normal serum, especially when FRAA blocks FR-α at the choroid plexus. High-dose folinic acid can bypass via the reduced folate carrier and support one-carbon flux.
Likely RCCX culprits to look at: C4 copy number and long vs short C4 with HERV-K(C4), TNXB loss or TNXB–CYP21A2 hybrid alleles, and common CYP21A2 deficiency variants or pseudogene conversions. (And hope you get lucky - much of RCCX still escapes us) These do not prove causation for CFD, yet they explain why this subtype clusters and why folinic acid helps the FRAA-positive group.
So I'd probably say this (might) be a non-verbal type of ASD caused by RCCX, unlike the type caused by dendritic abnormalities.