How much is attributed to nature? This is called genetics. How much is attributed to nurture? This is known as epigenetics, the environment. Dr. Mark A. Cruz posed these questions to a room of doctors of multiple disciplines during a session of the Airway Focused Dentistry Mini-Residency he co-developed. He then highlighted the history of DNA.
In 1953, two scientists were sipping on local ales before they announced the "secret of life" – DNA. Ten years later, the genetic code was discovered. DNA technology became a reality in 1970s. The first biotech company was established in 1977, which was eventually followed by the FDA's approval of the first recombinant DNA product – human insulin. In 1988, the Human Genome Project was initiated and completed in 2003.
"So, we pretty much had mapped out the entire human gene at the cost of a billion dollars," Cruz said.
The Human Genome Project identified over 30,000 discreet structural and regulatory proteins within 23 pairs of human chromosomes. Each gene can produce eight to 10 variations, or isotypes, through a process called alternative splicing. This process is influenced by the environment and results in several hundred thousand different proteins.
"It was believed that the Human Genome Project would give us the answer to most diseases and dysfunctions, but, interestingly, this couldn't be further from the truth," Cruz said. "In fact, they mapped only a few pure genetic diseases or conditions."
DNA has two types of information – the genes encoding the information and the gene regulatory network that specifies the behavior of the gene. He then explained examples of epigenetics, the study of heritable changes that occur without a change in the DNA sequence. The most fundamental action between muscles and bones is mechanical.
This response is truly epigenetic as first described by Conrad Hall Waddington in 1957. It is not inherited but controllable at the level of the gene and leads to a particular phenotype. The phenotype occurs via genetic (genotype) and epigenetic (environmental) influences. Environment plays a major role in the phenotype. Understanding this will help doctors with diagnosis and intervention, Dr. Cruz explained.
For example, dental crowding and various types of malocclusions are far more prevalent in industrial countries or areas as compared to urban populations or more agrarian populations. This is due to inadequate facial growth from diminished mechanical loading. Muscle contraction patterns are an intrinsic part of the way animals interact with their environment.
It began about 10,000 years ago when humans became agrarian, evolving from the hunters/gatherers to controlling their food supply and altering it. Humans' transition from hard to soft foods has occurred in the past 100 years. Dr. Cruz showed a slide that demonstrated the difference between the ancient skull and the modern man.
In 16th and 17th century skulls, the bony structure defining the pharynx is significantly larger than in modern humans. Our craniofacial growth has changed dramatically in the past 500 years, and it has accelerated. Our airways have diminished in size as a result of our environment. We have fundamentally changed as a species. Epigenetics is much more important in determining health and well-being for the genotype throughout life than was initially understood historically, Dr. Cruz explained.
Dr. Cruz studies the history as well as various medical cases and studies of genetics versus epigenetics to better understand the effects on the airway. As Dr. Cruz and other doctors better understand the genetic and environmental effects on craniofacial development and the airway, they believe they will be better able to diagnose and treat airway problems such as sleep disordered breathing.