Excerpted from: Rethinking Gender-Specific Medicine
One of the most unexpected and valuable benefits of thinking so deeply and meticulously regarding the nature of women’s biology, surprisingly, has been a new view of how to investigate the unique biology of men. Instead of simply assembling male cells, animals or humans for scientific investigation to answer questions and test hypotheses that we assumed would be identical for both sexes, we are asking very different questions about men than we have ever asked before. What are the particular problems of males? How can the information we’ve learned about women be applied to the prevention and amelioration of illness in men? Even the willingness to consider men unique, to look at their issues with the same exclusionary concentration that we have used in our exploration of women is shaping a whole new field of scientific investigation. Here are some of the more fascinating facts about men that are unique to their sex – facts that should prompt us to formulate and address proposals, and in doing so, improve the quality and, importantly, the length of men’s lives.
Men have only one X chromosome. Women enjoy the luxury of two, in spite of the phenomenon of lyonization, in which one of the two is randomly chosen for inactivation and the genes carried on it extensively silenced. Some, however, remain active. These ‘surviving’ genes may have profound effects on structure and function, either directly or through their governance and modulation of other genes. Moreover, lyonization is incomplete until the time of implantation, and this double complement of the genes that are responsible for virtually every aspect of tissue organization and function may give the female not only a different early physiology compared with the male, but a distinct survival advantage. Lyonization also produces what might be viewed as a heterogeneous reserve of genetic material in the female, since the silencing of one of the pairs of X chromosomes is random and not the same for all cells. An equally fascinating difference between the two sexes is the result of the phenomenon of imprinting, in which some genes transmitted to the fetus are expressed only from the maternal allele and others only from the paternal allele. Since the female has an X chromosome from each parent, she can transmit both paternal and maternal X-linked genes; males can only transmit their X-linked genes to females and not to males. These are only a few of the profoundly important sex-specific aspects of mammalian biology that may have far-reaching effects on function and length of life. It is clear that the male fetus is more fragile than the female and, for poorly understood reasons, becoming more so: even though there are more males conceived than females, the ratio of surviving males to females is decreasing throughout the industrialized world 1. In Japan, for example, the male-female ratio of miscarriage has increased steadily from 1.34 in 1972 to 1.72 in 19962. Certainly, the molecular biology of fertilization and implantation would prove a fascinating and important area of future gender-specific investigation.
Legato MJ. Rethinking Gender-Specific Medicine. Women’s Health. 2006;2(5):699-703. doi:10.2217/17455057.2.5.699
1. Davis DL, Gottlieb MB, Stampnitzky JR: Reduced ratio of male to female births in several industrial countries. JAMA 279(13), 1018–1028 (1998).
2. Mizuno R: The male/female ratio of fetal deaths and births in Japan. Lancet 356(9231), 738–739 (2000).