Excluding illnesses that affect specific sex organs (e.g., endometriosis, prostate cancer, uterine cancer), are there any diseases that exclusively (or almost exclusively) affect one sex?
The only example I could think of is ALD (andreno-leuko-dystrophy), which mostly affects males.
I’m sure there must be others.
There are a number of genetic problems based on the X chromosome that normally affect males almost (but not totally) exclusively. The reason for this is that they are recessives and in females the “good” gene on the other X chromosome masks their effects – unless the woman is homozygous for the trait, which happens extremely rarely. Some of these, like hemophilia, would definitely be regarded as illnesses; others, like pattern baldness, would not.
Expanding and clarifying on that;
In females, the “normal” X chromosome will be dominant over the “problem” X chromosome, making them “carriers” of the problem trait but not themselves sufferers from it. In males, of course, the unpaired X chromosome will code for the problem. Like this, with red indicating the problem gene:
Father: XY (no problem)
Mother: XX (no evident problem, but carrier)
Daughters: XX or XX (no problem, half are carriers)
Sons: XY (no problem) or XY (shows problem trait)
Only from a father suffering from the trait (XY) and a mother who is a carrier (XX) will any daughters show the trait, being XX, which will normally happen only extremely rarely.
I beleive color blindness is almost exclusively male. Of course the only reason I know this is becuase a color blind female friend of mine told me how rare it is, so take it FWIW.
Factor VIII hemophilia is manifested in males.
Turner’s syndrome is only seen in females.
Aren’t there some genetic defects which only show in females because the male embryos aren’t viable?
IIRC, females CAN become hemophiliac, but only if a female carrier marries a male hemophiliac. Then ALL of their children will inherit the disease, male and female.
Not exactly. Half the sons and half the daughters of a female carrier and a male hemophiliac will be hemophiliac. Half of the daughters will be carriers, half of the sons will be normal.
Female carrier: XX
Male hemophilaic: XY
Offspring:
Daughters:
XX carrier
XX hemophiliac
Sons:
XY hemophiliac
XY normal
If a female and a male hemophiliac were to marry, then all offspring will be hemophiliac.
Slight clarification: this assumes that the “problem” trait is recessive: there are X-linked dominant diseases as well. Hereditary rickets is an example of this.
True. But an X-linked dominant would not be sex-specific, since having it present on an X chromosome would make you susceptible to it, regarless of whether that chromosome’s “mate” is another X or a Y.
Red-green colorblindness is ten times more common in men than women. Frequently, it’s referred to as exclusively male although I am living proof that it is not. The statistic I heard was 1/2 of 1% of women in the world are colorblind which makes it statistically rare but, in a population of 6 billion+, makes for a rather large absolute number measured in millions.
Other forms of colorblindness, such as achromotopsia (which is rare no matter how you look at it) affect both sexes equally.
Turner’s syndrom is only seen in females because it involves having an unmatched X chromosome (she is one short of a full complement). The male equivalent, an unmatched Y, is completely non-viable and will not survive even very far into gestation.
Factor VIII hemophilia CAN manifest in women, but it is exceedingly rare. A few cases have cropped up in the past century or so since medical care has enabled boys with hemophilia to regularly live long enough to reproduce, and enough of them have done so that chance has brough sufferers and carriers together, but once the girls hit puberty they have a distressing tendency to come near to bleeding to death once a month or so.
Well, a female would have twice the chance to get it as a male, having two Xs which could be bad. But dominant genetic disorders are very rare, since they’re easily selected against evolutionarily.
While we’re here, what’s the mechanism by which normal vision can be dominant over colorblindness in females? As I understand it, in each of a normal woman’s cells, one of the two X chromosones, chosen randomly, is deactivated. This selection occurs early in embryonic development, and when those cells split, the daughter cells have the same chromosone deactivated as the parent cell, so large contiguous patches of the adult body will have the same chromosone. It seems like an eye, or even both eyes together, should be small enough to be contained entirely within one of those homogenous patches, which would mean (if my understanding were correct) that a woman with only one colorblindness gene could still be colorblind, if her eyes just happened to be formed from cells with the “good” chromosone deactivated. What am I missing, here?
Oops, already answered.
Two slight hijacks on colorblindness:
What genetic mechanism would result in the 10:1 skew towards males? That seems like an odd situation – way too high for a sex-linked recessive, but also a statistically significant ratio indicating that some sex-linked selection is at work.
Broomstick, would you be willing to discuss (here or in a new MPSIMS or other thread) how you perceive the world? I mean, I can visualize the idea that two colors look identical to you – I’m part of the large group that sees indigo as simply a dark blue, the color that “colonial blue” would be the pastel of, rather than a distinct hue. Obviously, when the top (or left) stoplight bulb is glowing, you know to stop, and to go when the bottom (or right) one comes on. And no doubt Christmas decorations in red-and-green must look bizarre to you. But do you perceive any difference between what non-colorblind people would see as “red” and what they’d see as “green”? Is there a contrast that displays itself to you in some way? Please don’t take offense if this is too personal, but the idea of variations in perception has always intrigued me, and you’re the sort of person who can give clear, coherent answers about it.
Similarly, Klinefelter’s syndrome (trisomy XXY) is only seen in males. Other trisomies of the sexual chromosomes are XXX (female) and XYY (male).
Does post-partum depression count?
You aren’t missing anything.
It is entirely possible that a woman could be colorblind under the scenario you describe and it probably does happen.
I recall reading about some instances where a person was colorblind in one eye and not the other - probably due to this sort of situation.
Or a lack of detection.
Despite being accepted to art school and working as a professional artist, my color vision “problems” weren’t detected until I applied for a 3rd class medical for a pilot’s license. Clearly, “defective color vision” (the term the FAA uses) is not nearly as handicapping as the general public seems to think.
Routine screening for color vision problems isn’t done for boys - it is often skipped entirely for girls in the belief that girls are never colorblind. So, unless you screen everyone you can’t discount the possibility that the 10:1 ratio has a large sampling error in it.
I’ve discussed this in several other threads, related to vision and related to flying.
First of all, not everyone who has variant color vision is truly color blind - technically I have deuteranomolous trichromacy. That’s a fancy way of saying my eyes don’t see the green part of the spectrum as well as the average human does. So I do, in fact, see the color green, particularly when it’s a deeply saturated hue. Where I have problems is with pastels (where there is less light in the affected color range reflected towards my eyes) and tertiary colors (where other hues compete for attention with the weakly detected green).
So, for example, I have a coat that for years I’ve thought of as a brown. Maybe a greenish brown/bronze in some lights, but basically when I look at it I see brown. Apparently everyone else sees green. A sort of brownish, subdued green, but green nonetheless. What people describe as “emerald green” I’d probably call blue. So where the debate would arise between you and me is in colors that are straddling the line between clearly delinated “green” and other shades.
Traffic lights are supposed to have a blue component in the green lenses to make it easier for people with color vision problems (including those who truly lack the ability to see green, which also occurs). Well, some of them do and some of them don’t. I have found that people with normal color vision frequently can’t see these differences that, to me, are obvious.
In aviation, quality control for standard colors is apparently much better than for traffic lights. The US standard is that you can reliably perceive certain colors as different from each other and identify them, not that you can see them “correctly”. Thus, although what the FAA calls “green” I perceive as “blue”, since I can consistently and reliably distinguish it from other colors used for signals and such I have an unrestricted license. If I was not able to do this I would have been issued a restricted license that would only permit me to fly in conditions where distinguishing key colors are not critical to safety.
Another area where color vision differences are significant are with camoflague - the standard “camo” used for clothing and tarps is designed to fool normal eyes. In WWII the British sought out and employed those with true red/green colorblindness to use as spotters because their eyes weren’t fooled. That still didn’t make these gentleman and more capable of matching their socks. And that only applies to those with a true lack of perception of part of the spectrum - camo patterns work with folks like me as well as it does for the norm.
As for how this has affected my life - well, probably not much since it wasn’t caught until my 30’s. It may well have had an effect on some of my artwork, but not in any untoward way. I do find that some color combinations I can’t stand others can and vice versa, but that may or may not have anything to do with my different color perception. When wearing certain colors I will have my husband double-check my attire to avoid fashion offenses, but for the most part I avoid such situations/color combinations entirely.
It may be that the more severe the color perception defect the more the person relies on shape and texture. One of the current authorities on color vision is, oddly enough, only capable of seeing in monochrome. An interesting book on the topic is Oliver Sach’s Island of the Colorblind which discusses achromotopsia, or true complete colorblindness where the eye lacks working color receptors. Those folks pretty clearly perceive the work in a very different manner.
Hemochromatosis, a disease caused by (or defined as) too much iron in the blood, affects mainly males, because women lose a lot of iron every month during menstruation, so it’s much harder for them to build it up to dangerous levels.