Gender-Specific Medicine and the

Genome:A Complex and Evolving

Tale

Marianne J. Legato, M.D., F.A.C.P.

Professor of Clinical Medicine, Columbia University

Director, Partnership for Gender-Specific Medicine at Columbia

Adjunct Professor of Medicine, Johns Hopkins

The past twenty years have witnessed a profound series of changes in our approachto and our achievements in biomedical investigation.

As a result, we have a radically new viewof normal human biology and the pathophysiology of disease and indeed,of the nature of life itself.

Instead of “what are the differencesbetween male and female?”,many scientists are asking: “What does it mean to be human?”

Traditional Biomedical Research Has

Made men normative for the entire population. Paradoxically, there has not been a systematic consideration of their unique, gender-specific features.

Not grappled with the extraordinarily difficult and most important issue of teasing out what characteristics are hard-wired as a result of biological sex and which are the consequence of social forces and environment.

Critics of the biomedical model

have demonstrated that:

“What is normal depends on who is being compared to whom,that many diseases have social and environmental causesthat illness rates and severity vary from place to place, and that the values underlying medical research, practice,theories and knowledge are deeply biased by the practice situations and social characteristics of the dominantgroup of medical professionals-physicians.”

J. Lorber. Gender and the Social Construction of Illness. SagePublications, Thousand Oaks, CA 1997. Quoted by Bird CE in10.1016/50277-9536(98)00420-X

What Influences “Health”?

Biomedical and sociologic experts often disregard and even disparage each other, particularly when funding is scarce.

Assumptions about health influence practice (The notion that women are relatively immune to coronary artery disease is still deep seatd in medical practice.)

There are gender differences in health behaviors of men and women the level of attention given to preserving male and

female health the societal roles expected of males and females.

These patterns may shift over time.

Anne Fausto- Sterling: without absolute social equality we cannot know the absolute differences between men and women.

What Influences Biomedical Investigation?

Public interestThe investigator:

Innate ability.

Previous experiences andtraining.

Prejudices and misconceptions.

1990-2010: How Far Have We Come

and Where are We Now? We are more aware of the extent and

complexity of the sex and gender specific properties of living organisms.

We are exploring how the intricate dance between the genome, hormones and the environment creates the phenotype.

We are inserting mechanical components into humans, including into their brains. We are also creating completely mechanical entities; robots capable of heretofore unimagined complex maneuvers.

The new age of synthetic biology is transforming our understanding of what constitutes life. For the first time in the history of the world we have the power to generate new forms of life, themselves capable of reproduction.

Modern Scientific Investigation:1940’s to 1980’s

The Bikini View of Women’s Health

The New Science of Gender-Specific MedicineAnd the Beginning of the Genomic Era

2000:GenomicMedicine

2003:ENCODE

1994-2000

Gender-

Specific

Medicine

1988-Direct

Investigation of Women

2010:

Synthetic Biology

2000:Robots

Some Important Issues Is it ever possible to separate what is

hard-wired into the organism by virtue of biological sex and what is the result of the impact of other factors on the phenotype?

What is the impact of biological sex on gene expression?

Given the complexity of how the phenotype is determined, how powerful/useful will the delineation of an individual’s genome be in predicting disease and in choosing therapy?

To what extent will mechanical parts augment human abilities? What does it mean to be ‘human’?

What role will synthetic biology play in the nature of life on this planet?

Is it ever possible to separate what is hard-wired into the organism by virtue

of biological sex and what is the result of the impact of other factors

on the phenotype?

“Sex-specific?”

“Gender-specific?”

(It is impossible to separate the organism from its

experience.)

“There is no gene-controlled inheritable trait that cannot be altered by the environment…Humans enter the world as a work-in-progress…Nature/nurture is not an either/or duality but, rather, represents a both/and type of complementarity.”

Leonard Schlain. Sex. Time and Power. Penguin Books. New York. 2003.

The Complex Dance Between the Genome And Experience:

Environmental Epigenomics.

How Environmental Factors Impact the Phenotype

Environmental factors act bymutating promoter and coding regions of genes modifying CpG methylation at critically labile

genomic regions. (Waterland R and Jirtle R. Nutrition 20:63.2004)

Epigenetic mechanisms include chromatin folding and attachment to the nuclear matrix, packaging of DNA around nucelosomes, covalent modifications of histone tails and DNA methylation. (Dolinoy DC and Jirtle RL.Environ. Mol Mutatgen.49:4.2008)

Regulatory small RNA’s and micro RNA’s impact gene transcription. (Matzke M and Birchler J. Nat Rev Genet 6:24.2005)

How Experience Changes the Brain

Neural changes associated with environmental enrichment: increase in brain size, cortical thickness, neuron size, dendritic branching, spine density, synapses per neuron and glial numbers. (Kolb B and Whishaw IQ. Annu Rev Psychol.49:43.1998)

Modulation of Experience-dependent Change Age: neuronal loss and dendritic growth: an area of controversy. Sex hormones: essential to sex-specific development of the brain and

to maintain the sex-specific characteristics of the brain throughout life. (Stewart J and Kolb B. Behav.Neural Biol.49:344.1988 and Brain Res.654:149. 1994.)

Neurotropins Stress:

chronic excess of glucocorticoids is toxic to neurons. (Sapolsky RM. Stress, the Aging Brain and Mechanisms of Neuronal Death. MIT Press. 1992)

Early life experience and major stressful life events produce dysregulation of serotonergic systems. (Gardner LK et al. Brain Research Elsevier.2009)

June 26,2000:The White House announces the completionof a rough draft of the human genome.

April 14, 2003:The Human Genome Project announcesa much more complete and accurate version.

The New World of Genomic Science

Gender and the Genome:

Why do we have two sexes?How do they differ?Which is hardier?

Sexual Dimorphism is Achieved Not Only by Gonadal Hormones but by the Direct

Effect of X and Y Genes.

The discovery of the gynandromorphiczebra finch: this bird has male plumageand a testis on the right side of the body and female plumage and an ovary on the left side.the brain was also sexually dimorphic; braintissue on the right was genetically male andthat on the left female. The hormonal milieu of the bird was obviously homogeneous.*

*Agate RJ et al. Proc. Natl. Acad Sci USA100:4873 2003

The X chromosome*

Contains 1,098 genes; only 4% of all human genes: gene density is low and gene length is lower than any other of the chromosomes annotated to date. (Furthermore, only 33% of the chromosome is transcribed.)

Only 54 of these genes have functional homologues on the Y chromosome.

Many of the genes that have to do with intelligence may be located on the X chromosome and may be closely linked with a gene dictating preference for intelligent males.

Almost 10% of diseases with a mendelian pattern of inheritance are X-linked.

*Ross MT et al. The DNA sequence of the human X chromosome. Nature 434:325-337. 2005.

“Functional or developmental themes have rarelybeen ascribed to whole chromosomes in eukaryotes.

instead, individual chromosomes appear to contain motleyassortments of genes with extremely heterogeneous patterns

of developmentally regulated expression.

We speculated that the human Y chromosome might be a

functionally coherent exception…”*

*Lahn BT and Page DC. Functional Coherence of the Human Y chromosomeScience.278:675-680.1997

The Y Chromosome:a New View

The Y Chromosome:Revising the Wasteland Model*

It is an unique chromosome: Common ancestry and persistent relationship with the X

chromosome Present only in males Does not combine with its partner along 95% of its

length (called the NRY or non-recombining portion of the Y chromosome)

Tendency of its genes to degenerate during evolution Unique coherence of gene content

Contains 78 genes (almost double the previously known tally) which make up <1% of the genome.They encode only 28 distinct proteins.

The Y chromosome can repair itself as a result of its palindromic structure. A backup copy of each of the genes they contain exists at each end of the sequence.

Lahn BT and Page DC. Functional Coherence of the Human Y Chromosome. Science 278:675-680.1997

Male Driven Evolution*Almost all new mutations are derived from

the father. (Makova KD and Li WH. Nature 416:624-26.2002)

Oocytes spend most of their lives in relative dormancy . Sperm are produced in huge numbers and have much higher metabolic requirements.

Male: female mutations in primates is about 3-6:1. Mutations result fromReplication errorsDNA fragmentation

Variability in the male germ line creates the genetic diversity that fuels the evolutionary process.

*Aitken RJ and Krausz C. Oxidative stress, DNA damage and the Y chromosome. Reproduction122:497-506.2001

Given the complexity of how the phenotype is determined, how powerful/useful will the delineation of an individual’s

genome be in predicting disease and in choosing

therapy?

“Skepticism about genomics runs high….Some …perceive genomics research as a low-yield

investment at best and as a dangerous opportunity cost at worst, which undercuts efforts

to address social and environmental causesof ill health.”

Combining Genomics with Epidemiology:

Balancing Population Based with Individually Targeted

Prevention/Treatment Strategies. Is increasing attention to genomics

useful for the public health? Will it widen the gap between richer and poorer members

of society? Will it reinforce racial stereotyping? Will it lead researchers to miss factors that contribute to

disparities more substantially than genomics?

The new science of human genome epidemiology: assesses* Prevalence of gene variants in different populations Magnitude of disease risk associated with gene variants Magnitude of disease risk associated with gene-gene and gene-

environment interactions Validity and effectiveness of genetic tests for screening and

prevention.Khoury MJ et al. Am J Prev Med 33(4).310-317.2007

“The question of how genes are definedand regulated is deceptively simple.

The emerging picture of gene regulationdepicts interdependent layers and webs

of control consisting of interactions of DNA withregulatory proteins and RNA molecules that are

akin to the interactions that occurin computer circuitry.”*

Feero WG et al. N Engl. J. Med 362:21.May 27, 2010

The Human Genome Project:Is It the Holy Grail?*:

The Notion of Biological Determinism

“The assumption that genes are the carrier of our destiny... places reductionist explanations to behavior above all others and, in so doing, allocates other causes such as environment to subsidiary roles.”

Genes are not the determinant mechanism in a biological process, but part of an interaction between the genes and the organism as a whole.

Organicism: a more complex and less popular view, which maintains that reductionism is inadequate to explain living systems. It maintains that one must look at the organizational structure of the organism, not just its disparate parts.

Morse A. Searching for the Holy Grail: the Human Genome Project and Its Implications.J Law& Health.13:1-34.1998.

“The idea that the human genome can be the

Rosetta Stone for disease ignores physical, chemical

and environmental factors.*

Keller EF. Master Molecules, in ARE GENES US? Carl F. Cranor ed. 1994.

What is the impact of biological sex on gene expression?

The Genetic Gender Gap: The Sexually Dimorphic

Gene* Thousands of genes showed sexual dimorphism in liver, adipose

and muscle; hundreds of genes were sexually dimorphic in brain.

These differences are highly tissue specific; thousands of genes identified were involved in tissue-specific biological functions and/or pathways relevant to common diseases and showed tissue-specific chromosomal enrichment.

Only 27 genes showed consistent direction , i.e. all female or all male biased in all tissues.

A significant portion of sexually dimorphic genes are located on the sex chromosomes, but some are carried on autosomes as well.

*Yang X et al. Tissue-specific expression and regulation of sexually dimorphicGenes in mice. Genome Research.16:995-1004.2006

Sex Impacts Gene Expression*

“We saw striking and measurable differencesin more than half of the genes’ expression patternbetween males and females. We didn’t expect that.no one has previously demonstrated this geneticgender gap at such high levels.”**

*Yang et al. Genome. 2006 **Thomas Drake, C0 investigator

The Genomic Era

Is manipulating the genome interfering with evolution orby definition, a continuation

of the process?

What Scientists are Doing

Taking genes out and inserting others.

Creating biologic specimens capable of reproduction.

Giving us an increasingly precise picture of who we are and the possibility of changing it.

Evolution is no longer “natural selection”.With the advent of

genetic engineering,we can- and are-

changing very natureof created life.

Imagine:

Human cloning

Engineering the characteristics of new(human?) beings prepared for specificfunctions (like war, for example)

Prolonging the life span indefinitely

Creating new biological systems capableof reproduction (and if this is so, alsocapable themselves of evolution)

Genomic Science and Sex

Will it be an advantage to retain two sexes?

If we eliminate biological sex in new forms of life before we understand the nature and extent of its expression on genes, what will be the consequences to form and function?

Does the study of the impact of sex on gene expression deserve more attention? Genomic scientists are not always considering the impact of biological sex on their data.

“If the molecular, cellular, and genetic machineryused to conceive, develop, and operate a human

were designed rather than the result of evolution, humans would be different

and life would look different.”*

*Olshansky et al. What if Humans were Designed to Last? The Scientist. 21(3).28

What are scientists worrying about?

Consider the Impact OfGenomic Science On

The environment

Economics

The nature and number of living beings

The redistribution of power (planned and unplanned)

“I chide Goldblatt* for the incredible naiveté he and the Defense Sciences Office displayedin not thinking its plans to enhancehumans would arouse controversy….didn’t it occur to anybody that youwere playing with fire?”

Joel Garreau(in Radical Evolution)

*Michael Goldblatt, former head of the Defense Science Office

What Scientists are Saying

We are changing the rate and mechanisms of the evolution of living things profoundly.

If there is a choice between preserving the earth in a viable state or continuing the human race, we will probably opt to continue the race.

“My guess is that if the question of human extinction isever posed clearly, people will say that it’s all very well to say we’ve been a part of nature up to now, but that at thisturning point in the human race’s history, it is surely essential that we do something about it; that we fix the genome to get of ridof the disease that’s causing the instability, if necessary, we clonepeople known to be free from the risk, because that’s the only wayin which we can keep the human race alive.

A still, small voice may at that stage ask, but right does thehuman race have to claim precedence for itself. To which my guess is the full-throated answer would be, sorry, the humanrace has taken a decision, and that decision is to survive. And,if you like, the hell with the rest of the ecosystem.”

Sir John Maddox, Former editor of Nature

Synthetic biology:

The ability to create livingorganisms from inert chemicals.

These new entities will probably be capable themselves of reproduction and of evolution into newforms.

Venter’s group has just reported the design, synthesisand assembly of a genome and its transplantation into a recipient cell to create new cells that are controlled only by the synthetic chromosome.*

Gibson DG et al. Sciencexpress./www.sciencexpress.org/20 May 2010/Page 1.

Venter’s Achievement:Reactions

Obama urges Presidential Commission for the Study of Bioethical Issues to focus on the research: “This development raises the prospect of important benefits….at the same time it raises genuine concerns…”.

George Church: “This milestone and many like it should be celebrated…But…the semi-synthetic myobacterium is not changed from the wild state in any fundamental sense. Printing out a copy of an ancient text isn’t the same as understanding the language.”

Arthur Caplan: “Venter and his colleagues have shown that the material world can be manipulated to produce what we recognize as life…Christianity, Islam and Judaism, among other religions, have maintained that a soul constitutes the explanatory essence of at least human life….All of these…views are cast into doubt by the demonstration that life can be created from non-living parts…”

Martin Fussenegger: “Venter…calls this ‘going from reading our genetic code to the ability to write it.” It may sound scary, but there is no guarantee that what will be written will make sense.”

"Ever since the discovery of nuclear fission, the possibility of powerful explosives based on it had been very much in my mind, as it had in that of many other physicists. We had some understanding of what this might do for us in the war, and how much it might change the course of history.”

“I am become death, destroyer of worlds.”

Doctor Atomic

Professor of Genetics at Harvard Medical School Director of the Center for Computational Genetics.

“…synthetic biology shares the potential…to generatenew entities that reproduce and evolve at will.

Whether we believe that these are immediate, distantor imaginary threats, the concerns are real….in additionto a code of professional ethics for synthetic biologists,

we need to watch for the rare cases where they transgress.”

George Church

Doctor Genomic

“Given the momentum and international characterof research in synthetic biology, it is already too late to impose a moratorium, if indeed onewas ever contemplated.”*

Tucker and Zilinskas: The Problems and Perils of Synthetic Biology. In The New Atlantis. AJournal of Technology and Society.

Prometheus, who gave men fire.

What Are Areas of Special Interest

As We Go Forward? Focusing a gender-specific lens on men, so that we can

better understand their greater vulnerability compared with women.

Expanding the current science of gender-specific medicine and testing its value in clinical practice.

Urging the exploration of the impact of biological sex on both the naturally occurring and synthetically created/altered genome.

Encouraging the colloquium between jurists, ethicists and scientists about the legal and moral implications of genomic science and synthetic biology.