I took another look at the biotin-related genes, now that I've more than doubled my sample size of genetic data for ME patients
I also took a look at the known and suspected biotin transporters. Controls are now matched by maternal haplotype, as an approximation for matching by ethnicity.
SNPs listed in bold red font are known missense mutations, and ones in purple font are known pathogenic missense mutations. Purple boxes indicate a genotype present in less than 1% of the population, red is 1 - 2.5% prevalence, orange is 2.5 - 5% prevalence, and yellow is 5 - 10% prevalence. Some results are blacked out for the ME patients and their matched controls because the new 23andMe chip doesn't test those SNPs anymore, and it makes things rather unbalanced if the controls have 23 sets of genotypes to look at when the patients only have 16.
Basically even the pathogenic mutations shown here typically don't cause disease by themselves. Though they can result in complete enzyme deficiency if one heterozygous mutation is combined with another. For BTD (as discussed earlier in this thread), rs13078881 reduces BTD enzyme activity by about half. In the general population and in the control group, prevalence is around 2%, yet is 8.7% for our ME patients.
The transporters (SLC5A6, SLC16A1, SLC19A3) look completely normal for the ME patients. But if adding together the rare genotypes occurring in BTD and HLCS, weighted based on rarity (10 for purple, 5 for red, 2 for orange, 1 for yellow), the ME patients would be 211, versus 58 for the controls. So nearly 4 times as much rarity in those genes for ME patients compared to the controls.
So interesting stuff, especially since biotin deficiency can cause many ME symptoms. Also, the major source of biotin is produced by gut bacteria, which could be another source of a problem for those of us with dysbiosis. Though it's hard to find any research clearly stating which bacteria are most responsible for biotin production, and there also doesn't seem to be much data regarding how the biotin gets from those bacteria to where it's needed.