A spotlight on ‘DNA’: the molecule of life

HD-Africa         April 25^th 2021

Author: Grace Njoroge a budding rare disease expert with a passion for Genetic counselling and advocacy

April 25^th is ‘DNA day’, a day that we celebrate the scientific advances in DNA, approximately 152 years since DNA was first isolated by Friederich Miescher. DNA is a chemical molecule carrying the genetic instructions of life for all organisms. The DNA molecule comprises of two strands that are organized into a double helix (twisted ladder) made up of a sugar and phosphate backbone. Attached to this sugar-phosphate backbone are 4 letters or bases namely A-adenine, T-thymine, G-guanine and C-cytosine. It is the precise pairing and ordering of these bases into the DNA sequence that determines the unique characteristics of each organism.  Errors occuring in the sequence of the 4-letter alphabet of the DNA molecule result in changes (mutations) that are associated with genetic disorders.

Years of studying this molecule responsible for encoding life’s biological instructions, DNA, has spanned great discoveries like its double helix structure in 1953 thanks to the work of James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin. In 1977, Fredrick Sanger developed rapid DNA sequencing techniques which are used to determine the order of bases in a strand of DNA. Through these advancements, it was possible to map diseases using DNA polymorphisms, with Huntington’s disease being the first disease to be gene mapped in 1983.

In efforts to better understand DNA’s functionality, an international collaborative research program, the Human Genome Program (HGP), was started with a common goal of mapping and identifying all the genes of human beings. A gene is the basic physical and functional unit of heredity – it carries the information that determines an individual’s traits. The HGP project was completed in 2003, providing a wealth of information about the genetic composition of human beings which continues to be used in understanding unknown genes and studying genes associated with diseases.

Genes play a role in the occurrence of diseases both infectious and non-communicable diseases like cancer and also rare diseases. Diseases classified as genetic disorders are caused by a mutation or variation of a specific or group of genes. Among these genetic disorders are, rare diseases, that currently affect 3.5% – 9.5% of the worldwide population, with 72% of the know 7,000 rare diseases being genetically linked. Currently, only 5% of rare diseases have approved treatments. The ability to rapidly sequence human DNA following the Human Genome Project allows scientists and researchers to study the metabolic pathways of these diseases and in turn identify possible treatments.

A pivotal discovery of the Human Genome Project was the revelation that all human beings are 99.9% genetically identical. However, the reference genomes used to build the Human Genome Project database were not inclusive of the African genome which is known to have the most variants. This is however changing thanks to ongoing work on African genomes. As a result, a recent study of the African genome by H3Africa uncovered about 3.4 million unique gene variants that had never been described before. Studying the African genome and its variations have contributed greatly to the treatment development of some cardiovascular diseases by studying the genetic variants in the PCSK9 gene which codes for a protein that regulates low-density lipoprotein cholesterol (LDL-C) levels. This shows the indisputable benefit and need for further research of the African genome. Humanity has not fully exhausted the benefits our enigmatic molecule of life `DNA`, before us lies a future where tailormade-medicine and gene therapies will become common place. In the meantime, the world continues to enjoy other fringe-benefits brought by the complete mapping of the human genome, in the form of DNA ancestry tracing and DNA fingerprinting. Using Y chromosome mapping the paternal ancestry is revealed, while mitochondrial DNA analysis reveals maternal ancestry. Understanding our ancestral DNA is important in knowing the intricate properties that make us unique, and the likelihood of developing a particular disease based on your genetic makeup. Finally, DNA analysis is a powerful forensics investigation tool, where, just like a fingerprint, each person has a unique DNA profile. This unique DNA profile or fingerprint aids in reliably identifying people involved in a crime. It is undeniable that the discovery of DNA, its structure, and functionality has been one of humanity’s greatest inventions.