April 29, 2022 - Written By: Maria Arini Lopez, PT, DPT
What is the Human Genome?
A genome is defined as the complete set of genes or genetic material in an organism.
Each human being has a distinctive genome made up of 4 nucleic acids—adenine (A), cytosine (C), guanine (G), and thymine (T). These nucleic acids pair together (A with T and C with G) in a sequence or unique arrangement to form that individual's deoxyribonucleic acid (DNA).
DNA is the genetic material which carries information that is passed down from parents to their child. Human DNA is found in 23 pairs of chromosomes located within each cell's nucleus. The nucleus is effectively a control center responsible for cellular growth and metabolism.
What are Genes?
Genes are segments or regions within DNA that contain the code to make one specific protein with a particular function in the body.
It is estimated that each human has around 30,000 genes. Variations of these genes, known as mutations, may cause genetic diseases to develop.
History of Unlocking the Human Genome
The Human Genome Project (HGP) was declared complete in April of 2003 even though initial drafts of the human genome were made available as early as June of 2000. But the HGP draft of the human genome was neither complete nor completely accurate.
Even though the HGP draft of the human genome was a sequence of roughly three billion letters, it was missing eight percent of the genes.
Over two decades later, researchers participating in the Telomere-to-Telomere (T2T) Consortium have produced the most complete draft of the human genome to date, addressing the remaining eight percent of the genome, with exception to the sex-determining Y chromosome.
These previously uncharted sections of the human genome consisted of very long, repetitive segments of DNA found at the end of the short arms of 5 different chromosomes, called telomeres, and the more difficult to access, denser portions in the center (called the centromere) of the chromosomes.
Two new DNA sequencing technologies— Oxford Nanopore DNA sequencing and the PacBio HiFi DNA sequencing—allowed these scientists to read much longer portions of the human genome with nearly perfect accuracy. Two decades ago, technology simply was not capable of analyzing these more difficult regions of the genome which have now come to light.
With these advanced methods, the scientists revealed over 200 million base pairs of sequence, predicting 1956 new genes, 99 of which are suspected to code for proteins. They also discovered around 2 million genetic variations within 622 medically relevant genes.
What does this Scientific Breakthrough Mean for the Rare Disease Community?
Over 80% of rare diseases are genetic in origin. The origins of some diseases remain unknown to this day, resulting in many individuals going undiagnosed.
This nearly-completed sequence greatly improves the research community’s ability to discover the origins of novel rare genetic diseases, finally bringing an end to several diagnostic odysseys endured by countless rare disease patients and their families, and providing deeper clarity into the biological implications of certain genetic mutations. This genome sequence will undoubtedly serve as a firm foundation for the development of effective treatments and potential cures for over 5600 rare genetic diseases.
The lives of millions of people living with at least one rare disease depends not only on an accurate diagnosis, but also on obtaining access to individualized treatments tailored to address their unique medical situations. Given the role whole genome sequencing can play in identifying and diagnosing debilitating human diseases, it is vital that whole genome sequencing becomes an affordable and accessible precision medicine diagnostic tool in the near future.
References and Resources
Human Genome Project FAQ. Genome.gov. Accessed April 19, 2022.
International Consortium Completes Human Genome Project. Genome.gov. Accessed April 21, 2022.
Nurk S, Koren S, Rhie A, et al. The complete sequence of a human genome. Science. 2022;376(6588):44-53. doi:10.1126/science.abj6987
University of California, Berkeley. Scientists have finally sequenced the complete human genome – and revealed new genetic secrets. SciTechDaily. Published April 3, 2022. Accessed April 19, 2022.
Researchers generate the first complete, gapless sequence of a human genome. Genome.gov. Accessed April 19, 2022.
Image: X Chromosome Sheme, DNA, Telomeres Are Protective Caps On The End Of Chromosomes, Short Arm, Long Arm. Dreamstime. Stock Vector - Illustration of short, sheme: 136091556. Accessed April 19, 2022.
Maria Arini Lopez, PT, DPT
Maria Arini Lopez, PT, DPT, CSCS, CIMT, CMTPT is a freelance medical writer and Doctor of Physical Therapy from Maryland. She has expertise in the therapeutic areas of orthopedics, neurology, chronic pain, gastrointestinal dysfunctions, and rare diseases, especially Ehlers Danlos Syndrome.