Last November I wrote that type 1 diabetes, unlike the vast majority of autoimmune diseases, is more common in men than in women. As it turns out, that is only true in populations where type 1 diabetes is more prevalent generally.
A few months ago I was browsing through OMIM (the Online Mendelian Inheritence in Man project). There are lots and lots of genes associated with type 1 diabetes. Two of those genes are located on the x chromosome. In combination with other genes- and ONLY in combination with those genes- one of the x chromosome genes increases susceptibility to type 1 diabetes in people who carry the DR3 marker (commonly found in type 1 diabetics of European descent).
The other one is the FOX regulator gene that I have heard lots about but never in terms that I really understand; it is linked to a whole bunch of complex immune disorders.
So, in populations where the DR3 diabetes genes are common, type 1 diabetes is more common in guys because it is a bit x-linked, and in other populations it is more common in women, because it is an autoimmune disorder.
In case you need a reminder of how X-linked disorders work: everybody has at least one X chromosome (fetuses without x chromosomes are miscarried), and people can have various numbers of x chromosomes. However, most men have one x chromosome and most women have two x chromosomes. Most x-linked disorders are recessive; if a person has one normal allele and one allele for a disorder, the person does not have the disorder. Therefore, having multiple x chromosomes protects you against having the disorder.
For instance, red-green color blindness, which is easily the most common x-linked disorder, occurs in roughly (ROUGHLY) 1 in 8 men, and 1 in 64 women.
That's because it works like this (pretending all sons are XY and all daughters XX):
If the father and mother have all normal color sight genes, none of the kids have this type of colorblindness, no matter the kids' sex.
If the father is colorblind and the mother has two normal color sight genes, none of the kids has this type of colorblindness, no matter the kids' sex.
If the father is colorblind and the mother is a carrier, half the kids are colorblind, no matter the kids' sex.
If the father is colorblind and the mother is colorblind, all the kids are colorblind, no matter the kids' sex.
If the father is not colorblind, and the mother is not colorblind but is a carrier (and roughly 1 in 6 women is), then half of the sons and none of the daughters are colorblind.
If the father is not color blind, and the mother is, all of the sons are color blind and none of the daughters are.