Genome Research: An Introduction and Primer

chillibreeze writer — Arati Arvind

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In 1990, international scientific community launched a massive program with a price tag of three billion dollars. The primary goal was to reveal the exact sequence of chemical base pairs which make up human DNA and to identify all the genes. Amidst all the criticism, the program which came to called Human Genome Project was concluded in record time, two years ahead of schedule and under budget. Genome is universally defined as the total DNA content of a haploid cell or half the DNA content of a diploid cell.

In April 2003, at a conference to celebrate the completion, it was a poignant moment when James Watson, Director of the project, discussed his own son’s handicaps and expressed hopes that HGP will help in understanding genetic basis of disease and thereby alleviate human suffering The conference ended with a positive note: Human Genome Project is a landmark achievement that promises to usher a new era of molecular medicine to prevent, diagnose, treat and cure disease. This was only the beginning!

The current genome sequence contains 2.85 billion genetic letters As, Ts, Cs, and Gs. It is accurate to an error rate of 1 event per 100,000 bases. To a layman it is all gibberish but to the initiated, it is wealth of knowledge. Embedded in this mass of bases are about 20,000 – 25,000 genes. While the objective of the Human Genome Project is to understand the genetic makeup of the human species, the project also has focused on several other nonhuman organisms such as E. coli, the fruit fly, the laboratory mouse and several pathogens. All this is available On Line, at the click of a button and all for free.

The project had started with ‘sequence now, interpret later’ kind of a philosophy. A rough draft of HGP presented in 2000 that allowed scientists to kick start several biomedical projects globally. Automation and super computers have eased/speeded up the task. Though the data presented stands for a reference genome, every individual has a unique genome and every disease has a genetic basis. Following are some examples of how genomic medicine can make a difference to available methods

Monogenic Diseases: The mapping of human genes is an important step in the development of medicines and other aspects of health care. Alterations in our genes, caused by mutations are responsible for clear hereditary diseases; there are an estimated 5000 of these, examples being sickle cell anemia, cystic fibrosis, Huntington’s disease and so on. Prior to HGP, connecting a gene to a disease was a slow, painstaking and often an inaccurate a process. Today it just takes a couple of days. In 1989, for example, it took nine arduous years to find the gene for cystic fibrosis; eight years later, Parkinson’s disease gene was mapped in only nine days.

Polygenic Diseases: The available sequences are only a first step in fully understanding the genome, because most of the genes involved in producing specific disease and their normal function are there to be deciphered and understood. Already several genes have been identified such as those related to deafness, breast cancer, stroke, diabetes, kidney disease and so on. It would have taken a long time in the absence of data provided by HGP.

DNA Microarrays in Diagnostics: Technological innovations have fueled genomic research. In 1991, researchers developed a method to embed DNA pieces of known sequences into glass squares, and use this array to pull out complementary sequences from a sample of unknown target DNA. These are the DNA Microarrays or DNA Chips that can answer several questions:

Which genes are turned ON in specific cell types?
Which genes are turned ON or OFF, in both host and pathogens in response to a particular disease?
Which drugs will help treat a particular condition in a particular patient?
Which individuals are likely to develop symptoms when exposed to a pathogen/environmental condition?

Seemingly endless questions and answers!

Developing new treatments at the molecular level: How genes work and exactly what happens at the molecular level to cause disease – understanding these has been now simplified. Bioinformatics tools have been used to elucidate drug designing that can lead to more effective therapies. A novel strategy has been tried in the treatment of myelogenous leukemia: a genetic flaw causes the gene product (a protein molecule) with an altered abnormal structure. A small molecule administered can attach to this protein changing its behavior by blocking its activity. Blood counts returned to normal in all patients treated with this drug as indicated by preliminary tests.

Single Nucleotide Polymorphisms SNPs: SNPs have gained much attention lately. These are single bases at a particular locus where individuals have differences in their sequences. These are the most common type of variations among people. Normally they occur once in every 300 bases; on an average, you may find about 10 million SNPs in the human genome. Commonly, they are found in the DNA between genes, acting as biological markers for a disease. Most SNPs have no effect on health or development. However when they occur within a gene or in a regulatory region near a gene, they may play a more direct role in disease by affecting the gene’s function. They have been found to play a role in predicting an individual’s response to certain drugs, susceptibility to environmental toxins, pathogens and risk of developing a particular disease. They are also helpful in tracking inheritance of disease genes in families. Studies are on for identifying SNPs associated with complex diseases such as cancer, diabetes, heart disease and so on.

All this has been briefly stated. Genomic research is a young and fast developing science. With so much relevance to prevent, diagnose, treat and cure, it is time medical fraternity take note of this field. Widespread demand for some such diagnostics can help in making them cost-effective. India with her own kind of disease pattern in populations will need more health management strategies

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—About our writer:

Arati says, "It has always been science for me. After decades of research and some teaching, now it is time to write science - simplified. My garden is a passion too, so is Indian music - not to mention reading, friends, window-shopping…"

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