In what follows, we are struck by the fact that all human beings are extraordinarily similar in composition -99.9% similar. So what is it that makes one person taller than another, or with better eyesight, or destined to acquire a disorder later in life? Can science finally crack the genetic code while we are still infants so that we may take preventive measures? Can science examine the DNA of an embryo and forecast all of that baby’s predispositions? Also provided is a list of a select 20 of the most commonly inherited disorders, as well as answers to the ethical questions that have arisen as a result of advances made in genomics -i.e. the science of the complete DNA of a human being.

 The evolution of genetics

After thousands of years of cross-pollinating and tinkering on the edges of genetics, scientific breakthroughs seem to be happening of late at a frantic pace. Soon the words “It’s genetic” will no longer carry that frightful finality, for researchers are fast unraveling the mysteries of heredity. Today the landscape is dominated by concepts such as gene splicing, gene cloning, “designing” babies, creating highly specialized drugs, and the further development of that long, winding molecule called deoxyribonucleic acid -DNA.

Genetic predispositionsThe “father” of modern genetics is universally considered to be the Augustinian monk Gregor Mendel who lived in what became later the Czech Republic. In experiments conducted on peas between 1856 and 1863, he established many of the principles of modern heredity. By cross-breeding peas in a controlled environment, he was able to manipulate such traits as height, shape, color and more. Mendel also studied the prevalence of traits in subsequent generations of peas. In his published work in 1866, he referred to hidden factors for what we now know as genes.

From cross-breeding to “genomics”

Cross-breeding had been known since well before that however. In Ancient Greece, Aristotle had thought that embryos were produced when semen was restructured by menstrual fluid in intercourse. And before that, prior civilizations had known how to influence the breeding of animals and plants to suit their needs. Thus more than three millennia ago horses were bred for speed in the Near East, and more than four millennia ago, Egyptians succeeded in breeding palm trees for a more abundant and qualitatively superior crop.

The post-Mendel era was subsequently characterized by roughly a few decades of slow advances followed by a century of explosive progress during which scientists from all corners of the globe tackled the bedrock principles of heredity. In that century the focus shifted from Mendel to heredity’s biological components, and from genetics, i.e. the study of genes and how features are handed down generationally, to genomics, i.e. the science of the complete DNA of an organism.

Medicine will always remember this date

A quarter of a century from now, most things in medicine will be referenced in terms of before and after that date –that accomplishment. This of course describes the spectacular announcement on June 26, 2000, that scientists had completed a working draft of the human genome (following a 10-year concerted effort involving hundreds of scientists around the globe and close to $3 billion in outlays). It had been cumbersome and expensive, but they had opened the “book of life” and had heralded the new era in which research is expressed for the most part as “what we had known up to that point” and “what we have learned since”.

Every human feature has a genetic component

Genetic predispositions 1Almost every feature in our body –e.g. our ear, eye color, liver and embedded disorders have a genetic component. That can be inherited or influenced by behavioral factors such as exercise or environmental factors such as tobacco smoke or other toxins. In addition, genetic components also determine our reaction to toxins and to disease. It is therefore important to understand the role of genes and the basic concepts of genetics.

We are all 99.9% Identical

The genome is the genetic blue print of a human (or organism) that is contained in its DNA. It is the sum-total of an organism’s hereditary information, and although people are 99.9% identical in their genetic make-up, differences in the remaining 0.1% is what health and disease is all about. Through the study of genomics and the interaction with the environment, scientists are better able to understand why some people get sick from certain infections while others do not. Mankind is now firmly anchored on the path of functional genomics and new insights into cancer, inherited disease, and the discovery of new vaccines and therapies.

Understanding Predispositions

A genetic predisposition translates into a greater likelihood of developing certain things, such as traits, allergies, diseases, temperament, a certain level of intelligence or many other features. It is not always the case that persons with predispositions should always end up with whatever they were predisposed for. The effect of the environment or other as-yet unidentified genes can also have an effect. Thus people who have predispositions are not certainly going to “express” the genes they inherited. Those genes can remain “unexpressed”. There are genes however that are always expressed, such as Huntington’s disease. Anyone with a predisposition to Huntington’s will eventually catch the disease, irrespective of other factors.

Genetic vs. behavioral or environmental diseases

The answer to what percentage of what happens to people is genetic versus behavioral or environmental depends on the individual and on the predispositions. We saw how in Huntington’s disease –as well as in cystic fibrosis, sickle cell anemia, Downs syndrome and some other diseases- the inherited genes will always result in the disease. Other, more complex diseases (e.g. type 2 diabetes or rheumatoid arthritis) depend to significant levels on behavioral influences. Thus a predisposition for type 2 diabetes can be viewed merely as a warning prompting lifestyle changes. Add to that multifactorial diseases that have behavioral as well as genetic components, type 2 diabetes again being a good example, for it has several genes that contribute to it. Other diseases are almost 100% behavioral, e.g. lung cancer, while yet others are 100% environmental, e.g. infectious diseases. A person who grows up in an abusive household may not be genetically predisposed to mental illness, but is certainly environmentally prone to it.

Genetic awareness and prevention or treatment

Is it useful for people to know that they are predisposed to certain diseases? Of course it is. They can discuss further tests with their physicians, catch the disease in an early stage, and remain alert to other symptoms that may show up. If someone for example has a family history of breast cancer and genetic tests indicate that they have one of the relevant mutations, they can then make sure to have regular mammography exams. Familial breast cancer is one of the complex diseases that may not necessarily express itself. Nevertheless, such individuals can benefit from being aware of their heredity predispositions.

Genetic testing

Genetic testing involves the analysis of a person’s DNA. Genetic tests are very specific and are used primarily for the following reasons:

  • Genetic predispositions 2Predictive testing is offered to a person who has a family history of a genetic disease, but has not yet developed symptoms
  • Diagnostic testing used to confirm or rule out a suspected genetic disease in a person with symptoms of the disease
  • Prenatal testing is performed during pregnancy to test the fetus for a genetic disease when there are reasons for the suspicions
  • Preimplantation testing is done on embryos produced through in vitro fertilization that are at increased risk of having a serious genetic disease

How genetic testing may soon affect all of us

It is hoped that genomics will accomplish for genetic disease what vaccines keep doing for infectious disease. Genomics is the way forward toward in preventing the manifestations of genetic disease. More significantly, the cost of “sequencing” is coming down fast. It is hoped that in the next few years research laboratories will be able to determine the entire genome sequence of every person at birth for less than $1,000. This compares with current costs in excess of $10,000 for a complete sequencing. This genomic roadmap at birth will enable doctors to prescribe specific tests for each individual as well as a recipe for a lifestyle that will improve one’s health by attacking a genetic disease before it expresses itself. Imagine a world in which each individual is in control of their inherited package. Patients will know what the risks are if they smoke, over-eat or lead a sedentary life style.

Next: significant clues for treating common diseases

The science of genomics paved the way for researchers to understand the basic structure of the genome. The last few years have been consumed with understanding the biology of disease, and while great strides have been made, very little of this research has yet to have a direct impact on patient health. That is what the next period will be about –understanding and developing the science of genomic medicine. Only after scientists have developed a firm grip on how genomic medicine can influence disease will advances begin pouring into the field of patient care. In the next 10 to 25 years, an expanding body of scientific knowledge about gene and disease biology will likely identify the genetic basis of most single-gene inherited disorders. Pathways that are thus involved in single-gene disorders may hold significant clues for the diagnosis and treatment of common disease.

There are four types of inherited diseases

Genetic predispositions 3A genetic disorder is a disease caused by the abnormalities of a person’s genetic material –i.e. a person’s genome.

  • Single-gene or monogenic: This type is caused by mutations that occur in the DNA sequence of one gene. A disorder occurs when a gene is mutated and can’t carry out its normal functions, causing disease. There are in excess of 6000 known single-gene disorders, and some will occur in roughly 1 out of every 200 births. Examples would be Huntington’s disease, cystic fibrosis, and other diseases.
  • Multifactorial or complex: This type is caused by a mix of environmental factors and mutations in multiple genes. It has a more complex structure that makes it more difficult to diagnose. Multifactorial inheritance is linked to high blood pressure, diabetes, Alzheimer’s disease, heart disease, arthritis, cancer, and other disorders.
  • Chromosomal: Chromosomes consist of DNA and protein and are located in the nucleus of each cell. Because chromosomes are carriers of genetic material, defects can result in disease. Down syndrome is a common disorder that occurs as a result of chromosomal disorders.
  • Mitochondrial: This is a rare type that is caused by mutations in the nonchromosomal DNA of mitochondria. Mitochondria are the cell’s power producers. They convert energy into forms that are usable by the cell. Examples of mitochondrial diseases would include Myopathy (a disease of muscle tissue), Acidosis (an excessively acidic condition of the body, dementia (a chronic disorder of the mental processes, and other.

Commonly inherited diseases and conditions


Among the most commonly inherited diseases




a decrease in number of   red blood cells (RBCs) or less than the normal quantity of hemoglobin in the   blood

Diabetes (type 1   and 2)

A condition that occurs when the body can’t use glucose (a type   of sugar) normally

Parkinson’s Disease

A progressive disorder   of the nervous system that affects your movement

Breast Cancer

A   cancerous growth that inhabits the tissues in the breast. Breast cancer is the most common   cancer in women and the second most common cause of cancer death in women in   the U.S.


Are abnormal reactions of the immune   system that occur in response to otherwise harmless substances


An abnormal expansion of   cavities (ventricles) within the brain that is caused by the accumulation of   cerebrospinal fluid

Cystic Fibrosis

This is a chronic lung   disease in children and young adults. it causes thick, sticky mucus to build   up in the lungs, digestive tract, and other areas of the body

Down Syndrome

This is the most common   and readily identifiable chromosomal condition associated with intellectual   disabilities


Researchers   believe that miscarriages are most frequently the result of random genetic   problems in the developing baby

Huntington’s   Disease

Aprogressive neuro-degenerative   disease causing uncontrolled physical movements and mental deterioration

Bipolar Disorder

One of several psychological disordersof mood characterized usually by alternating episodes of depression and mania

Tourette Syndrome

A neurological disorder   that includes involuntary facial, motor, and vocal tics

Cerebral   Palsy

A disorder of muscle tone or posture that is caused by   abnormal development in the immature brain, most often before birth

Autism   Spectrum disorders

(in   children and adults)

One of a group of developmental disorders   (as Autism and Asperger’s   syndrome) marked by impairments in the ability to communicate and interact   socially

Learning   Disabilities

A condition giving rise to difficulties in acquiring learning   skills to the level expected of those of the same age

Fragile   X Syndrome

A widespread form of mental retardation caused by a faulty   gene on the X chromosome

Macular   Degeneration

A medical condition which usually affects older adults and   results in a loss of vision in the center of the visual field


This describes any of several hereditary blood-coagulation   disorders in which the blood fails to clot normally

Malignant   Hyperthermia

A   hereditary condition in which certain anesthetics (in surgery) cause high   body temperatures and muscle rigidity


Ethical, discrimination, and other practical issues

As the science races forward, ethical, legal, and social concerns about evaluating genetic predisposition have come to light that didn’t exist even recently. Countries like the US have signed laws prohibiting discrimination based on genetic factors, but that hasn’t stopped these and other similar questions from arising. For example:

  • How privacy and confidentiality issues will be controlled
  • Health insurance companies could discriminate against anyone who has genes that might suggest elevated risk for disease
  • Employers could refuse to hire those who might need more time off if they got specific illnesses
  • Employers could screen for people with greater likelihood of intelligence
  • And fundamentally, is it always good to know how you are predisposed? How about getting a diagnosis at infancy about a disease that always expresses itself?
  • Should parents test their embryo for diseases that might result in abortion decisions?

So what can the lay person expect in the coming few years from the ongoinGenetic predispositions 4g research into genomics?

One task for genomics straight ahead is to apply continually refined genome-based strategies for the early identification, diagnosis, and treatment of disorders. Also, to find variations in the DNA sequence among people and determine their significance. These small differences (0.1%) may help predict a person’s disposition for specific disorders and response to certain pharmaceuticals.

In addition, “next-generation sequencing” (NGS) has already been influential and will be key to identifying diseases in the near future. When multiple genes are involved such as in the different cancers, traditional sequencing today remains clumsy and expensive. NGS allows for rapid analysis of multiple genes at a considerably lower cost. Genetic testing panels have come up for hereditary breast, colon, and other cancers.

As the costs of sequencing a human being’s DNA come down, the day will soon be upon us when one can order a kit online, spit into it, and read one’s health future, much like blood results appear now. Whether or not that is desirable is left to each individual. If that does not happen soon enough to affect us, it is bound to impact our children and grandchildren.

About Mike Takieddine, the author:

Mine has been a privileged life, first for having traveled all over as son of a diplomatic family, then for having had the opportunity to study at Oxford, and finally for a gratifying career in business, in geriatric home care, and in writing. I look forward to using this wonderful medium to discuss the various aspects of life that are of interest to my readers.