Why? Is it the genes, hormones, immune system – or behavior – that make men more susceptible to disease?
I see it as an interaction of all these factors and it is not unique to the SARS-Cov-2 virus – different responses between men and women are typical of many diseases in many mammals.
The numbers are bleak
In Italy and China the death of men is more than double the death of women. In New York City men are about 61 percent of patients died. Australia is preparing to have it similar results, although here it is mostly in 7Age groups 0-79 and 80-89.
One major variable in COVID-19 severity is age. But this cannot explain the gender bias seen globally because of the increase in male mortality rates the same in every age group from 30 to 90+. Women also live an average life six years longer than men, so there are more older women than men in a vulnerable population.
But then we must ask why men are more susceptible to diseases that put them at greater risk of COVID-19.
Men and women are biologically different
Men and women are different in their sex chromosomes and their genes. Women have two intermediate copies of chromosomes (called X). Men only have a single X chromosome and a small Y chromosome that contains several genes.
One of these Y genes (SRY) directs the embryo to become male by starting testicular development in the XY embryo. Testes make male hormones and hormones make babies develop as men.
In the absence of SRY, the ovaries form and make female hormones.
This is the hormone that controls most of the differences that are clearly visible between men and women – genitals and breasts, hair type and body – and has a big influence on behavior.
Y chromosome and hormones
The Y chromosome contains almost no gene other than SRY but is full of repetitive sequences (“junk DNA”).
Maybe “toxic Y” can lose regulation for aging. This can accelerate aging in men and make them more susceptible to viruses.
But a bigger problem for men is the male hormone released by the action of SRY. Testosterone levels are involved in many diseases, especially heart disease, and can affect age.
Men are also harmed by them low estrogen level, which protects women from many diseases, including heart disease.
Male hormones also influence behavior. Testosterone Levels has been credited with large differences between men and women in risk behaviors such as smoking and drinking too much alcohol, as well as reluctance to heed health advice and seek medical help.
Extreme difference in smoking rates between men and women in China (nearly half of men smoke and only 2% of women) can help explain the very high ratio of male deaths (more than double women). Not only is smoking a serious risk factor for any respiratory disease, but it also causes lung cancer, a further risk factor.
Smoking rates are lower and not gender based in many other countries, so risky behavior cannot in itself explain gender differences in COVID-19 deaths. Maybe the sex chromosome has another effect.
Two X chromosomes are better than one
The X chromosome contains more than 1,000 genes with functions in everything including routine metabolism, blood clots and brain development.
The presence of two X chromosomes in XX women gives a buffer if the genes in one X mutate.
XY males do not have these X chromosome reserves. That’s why boys suffer from many sex-related diseases such as blood disease (Poor blood clotting).
The number of X chromosomes also has a large effect on many metabolic characters separate from the effects of sex hormones, as revealed by studies in mice.
Not only do females have multiple doses of many X genes, but they can also have the benefit of two different versions of each gene.
This X effect explains why males die at a higher rate than females at every age from birth.
And another male problem is the immune system.
We have known that for a long time women have a stronger immune system than men. This is not all good, because it makes women more susceptible to autoimmune diseases such as lupus and multiple sclerosis.
But it gives women the advantage when it comes to vulnerability to viruses, because many studies in rats and humans to show. This helps explain why men are more susceptible to many viruses, including SARS and MERS.
There are at least 60 immune response genes on the X chromosome, and it seems that this higher dose and has two different versions gives women a broader spectrum of defenses.
Sex differences in disease – the big picture
Gender differences in frequency, severity and efficacy of treatment for many diseases are shown a long time ago. COVID-19 is part of a larger pattern in which men lose – at every age.
This isn’t just humans – this applies to most mammals.
Are sex differences in disease susceptibility merely a side effect of genetic and hormonal differences? Or are they, like many other traits, chosen differently in men and women because of differences in life strategies?
His recommended that male mammals spread their genes by winning competition for partners, so controlling risky behavior hormones is a plus for men.
It is also recommended that female mammals be selected for traits that enhance their ability to care for young children, hence their immune system is stronger. This makes sense for most mammals for centuries.
So the gender bias in COVID-19 death is part of a much bigger picture – and a much older picture – about sex differences in genes, chromosomes, and hormones that lead to very different responses to all types of diseases, including COVID -19.
Jenny Graves, Honorable Professor of Genetics, La Trobe University
Updated Date: April 20 2020 14:58:29 IST
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