Research updates
15 - Ethics and the Gene Map page 5
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5. The Human Genome Project Link to the Medical Research Council web site
 
What is the point of the Human Genome Project?
So what are the reasons for spending $2 billion (actually, less than half the profit made by BT in 1997) sequencing the entire human genome? The simplest answer is the medical benefits that are expected to follow. Determining the sequence of a gene often helps researchers to begin to unravel how the gene works. This can help in the design of new treatments for diseases.

Microscope view of chromosome 9 at 10,000 x magnification.
In the case of tuberous sclerosis, this is only just beginning. It seems that both the TSC1 and TSC2 genes are tumour suppressor genes. The absence of the proteins made by either of these genes may lead to a breakdown in the control of cell growth. A mutation in either of these genes therefore makes it more likely that the person develops tumours. These tumours can occur in a variety of organs including the heart, the kidneys and the brain. In the brain they can be seem with MRI (magnetic resonance imaging) scans. It is these brain tumours that are responsible for the seizures and associated mental problems.
Linkage studies showed that two separate genes, one on chromosome-9 and on on chromosome-16 were involved. Each of these two genes is responsible for about half the cases of tuberous sclerosis. The gene on chromosome-16, known as TSC2, was sequenced in 1993 but the gene on chromosome-9, TSC1, took longer to find (it had already been sequenced by the time it was found). Having spent years unsuccessfully attempting independently to map and sequence it, the research groups in the race agreed in 1996 to collaborate. Sharing all the information between them helped speed progress and success finally came in 1997. Sue Povey describes herself as being "so excited, so excited" the night they realised that they had cracked it. The finding was published on 8 August 1997 in the prestigious journal Science.
Where is TSC1?
Figure 5 shows a diagram of one strand of chromosome–9. The shorter arm of the chromosome is called 9p, the longer 9q. The longer arm is divided into three regions, numbered 1, 2 and 3. Region 1 is the region nearest to the centromere, region 2 is further away and region 3 is further still. Each region is divided into visible bands. Region 3 of chromosome-9 was originally divided into four bands but has now been further subdivided so that a total of 6 bands are recognised within the region: 31, 32, 33, 34.1, 34.2 and 34.3 - in each case the first digit, 3, refers to the region and the other digits refer to the band. The TSC1 gene falls within the 9q34 region - i.e. chromosome-9, arm q, region 3, band 4.
Figure 5. Roll over the highlighted words to show the sequence of diagrams
We can zoom into this region to see precisely where TSC1 is located. This picture shows a part of 9q34 that is 1.2 mega bases long. The TSC1 gene is only one gene in this region and is 60 kilo bases long.

1 megabase = 1,000,000 bases;   1 kilobase = 1,000 bases.

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We can zoom in further to see the structure of the TSC1 gene. The DNA of gene TSC1 is made of 23 exons with introns in between. The whole of the DNA is transcribed to messenger RNA (mRNA), which is then processed to remove the introns, which degrade and disappear. Finally, the processed mRNA is translated into a protein.
Treating tuberous sclerosis
At present, treatment for tuberous sclerosis simply involves trying to deal with the wide variety of symptoms. Understanding the molecular basis of the condition, increases the likelihood of finding treatments which will prevent the harmful symptoms from occurring. It should also help to explain just why the condition is so variable in its effects, with some people hardly being affected and others disabled for life. Looking much further ahead, now that the genetics of tuberous sclerosis are being unravelled, the possibility of gene therapy being used one day either to prevent or to treat the condition comes a step closer.