More women than expected are genetically men.
Sex chromosomes usually determine whether you are female or male. Women are XX. Men are XY. However, genetically, a few women are actually men. They grow up as women with a woman’s body, and most only discover well into puberty that they are different. The proportion was higher than expected.
You cannot see it if you do not know what you are looking for. One in 15,000 males is born and grows up as a girl. And neither these girls nor their parents know it. These girls do not discover anything different until puberty.
“Girls born with XY chromosomes are genetically boys but for a variety of reasons – mutations in genes that determine sexual development – the male characteristics are never expressed. They live their lives as girls and then women, and a few can even give birth. Our research, which is the first nationwide survey in the world, shows that this group is up to 50% larger than previously assumed. How these girls discover the facts and talk openly about their situation also varies greatly,” explains Claus Højbjerg Gravholt, who led the study and is Clinical Professor in the Department of Clinical Medicine of Aarhus University.
Together with colleagues, he is investigating why sex chromosome abnormalities occur and therefore how people with XY chromosomes can become women. Two types of genetic mutations mostly make the difference; these were previously referred to as Morris syndrome and Swyer syndrome but are now collectively referred to as disorders of sex development (DSD).
Those women are fit, with smaller breasts, narrow hips, taller than peers etc. But there are more signs and symptoms.
This has nothing to do with sexual preferences, or whether they are heterosexual, lesbian or they have some other sexual preferences.
In 2008, doctors reported a curious case report about a woman who gave birth despite the majority of her cells having XY chromosomes, typically held by people who are biologically male. A woman from Croatia sought medical attention when at 17-years-old she had not yet developed breasts, nor had her first period. Upon examination, the doctors didn’t find much out of the ordinary, aside from the absence of these signs of female puberty. Her genitals appeared normal, she had pubic hair and facial acne, was tall, thin, and intelligent. The only sign other unusual medical sign apparent to the doctors was that she had a hypoplastic uterus (her uterus was abnormally small). However, when they looked at her blood, they found that she had 46,XY, a disorder of sex development. What is interesting in this case is that the mother was 46,XY too according to a karyotype on her blood, and had gone through female puberty and given birth to her daughter despite the majority of her cells containing XY chromosomes. The team examined the mother, who had a typical female appearance, breasts, and external genitalia, though her pubic hair was sparse. Though her blood was found to be 46,XY, samples taken from elsewhere around her body were not so. Cells in her skin were found to be 80 percent 46,XY and 20 percent 45,X, indicating Turner Syndrome with mosaicism. This is where female individuals are missing an X chromosome in some cells but not others. Where one chromosome is missing from all cells, it is simply Turner Syndrome, and can cause much more prominent symptoms, such as a webbed neck, heart defects, swollen limbs, and infertility. More interestingly, her ovaries were found to be predominantly 46,XY (93 percent 46,XY and 6 percent 45,X), i.e. her ovaries contained chromosomes typically found in the cells of male individuals.
Girls with Swyer syndrome have an XY chromosomal makeup (as boys normally do) instead of an XX chromosomal makeup (as girls normally do). Despite having the XY chromosomal makeup, girls with Swyer syndrome look female and have functional female genitalia and structures including a vagina, uterus and fallopian tubes. Girls with Swyer syndrome lack sex glands (ovaries). Instead of sex glands, women with Swyer syndrome have “gonadal streaks”, in which the ovaries do not develop properly (aplasia) and are replaced by functionless scar (fibrous) tissue. Because they lack ovaries, girls with Swyer syndrome do not produce sex hormones and will not undergo puberty (unless treated with hormone replacement therapy). Mutations in several different genes are known to cause Swyer syndrome.
“Morris syndrome is now called 46,XY DSD: androgen insensitivity syndrome. These people have an extremely high level of testosterone and other male sex hormones, but the testosterone does not affect the foetal cells that usually develop into male sexual organs because of a mutation in the androgen receptor gene. These people therefore have male chromosomes but are women socially and in external appearance. They do not have internal female sexual organs, and they form testicles that remain concealed in the abdominal cavity.”