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SOME EARLY DISEASE-CAUSING GENES FOUND USING GENOMIC

Disease name Symptoms Year

SCREENING

identified

Chromosome

Chronic Granulomatous Disease

Poor immune system

1986

X

Duchenne Muscular Dystrophy

Muscle weakness, muscle deterioration

1986

X

Cystic Fibrosis

Difficulty breathing, poor lung function

1989

7

Neurofibromatosis

Benign tumors

1990

17

Fragile-X Syndrome

Mental retardation

1991

X

Huntington's Disease

Uncontrollable movements, brain deterioration

1993

4

Tuberous Sclerosis

Benign tumors

1993

16

Alzheimer's Disease

Loss of memory and brain function

1993

19

Breast Cancer

Tumors in the breast

1994

17

Glaucoma

Loss of eyesight

1997

1

Table 1 The Process of Disease-Gene Discovery

Table 1 The Process of Disease-Gene Discovery

Performing disease-gene discovery requires asking and answering five important questions: What does the disease actually look like? Do genes really play an important role in this disease? Can enough families with enough affected members be found to help study the disease? What are the genes? What do these genes do?

What does the disease actually look like? It may seem obvious that to study the genetics of a disease such as epilepsy (seizures), families with seizure

? sufferers should be studied. However, it is possible that genes are impor tant only in some, not all, types of epilepsy. It may also be true that different genes are important in different types of epilepsy. Thus it may be better not to study all seizures but only one type. For example, it might be better to study seizures that affect only one part of the body or that cause only a loss of consciousness with no effects on the rest of the body. Which type of seizures to study depends mostly on how important genes are for that particular type of disease.

Do genes really play an important role in this disease? There are many ways to see if genes are important in a disease (or a particular subtype of disease) without having to know what the genes are. Figuring this out requires studies that look at information from very large collections of fampopulation studies col- ilies and individuals. These are usually called population studies. lection and analysis of data from large num- One important type of population study looks at a large set of twins to bers of people in a p°p- see how often two identical twins (who have all the same genes) both have a disease and compares that to how often two fraternal twins (who are just like brothers and sisters in that they have only half of their genes in common) both have the disease. If genes are important, the identical twins will share the disease (be concordant) much more often than fraternal twins. For example, in over 80 percent of cases where one identical twin is diagnosed with autism, the other is also diagnosed with the disorder. When one fraternal twin, on the other hand, has autism, the other will have the disorder in only about 5 percent of cases. This suggests that genes have a very strong effect in autism.

Another way to see if genes are important is to look at a large set of adopted children who have the disease and compare how often their adoptive parents have the same disease with how often their natural parents have it. If the rate of the disease is much higher in the natural parents than in the adoptive parents, genes are likely to be important. For example, the fre-

ulation, possibly including related individuals quency of multiple sclerosis in the natural parents of people with multiple sclerosis is about 3 percent. Among the adoptive parents of people with multiple sclerosis, the frequency was much smaller and about the same as the general population.

Yet another way to see if genes are important is to look at the occurrence of the disease in the brothers and sisters of someone who has the disease. If the rate at which brothers and sisters have the disease is much higher than the rate in the overall population, then it is likely that genes are important. Autism again is a good example. The rate at which autism is found in the brothers and sisters of an affected person is about 3 in 100, which does not seem very high. But the rate in the general population is only about one in five hundred (0.2%). It is the comparison of these rates that is important, not just the actual frequencies.

Each of these kinds of studies requires looking at a lot of people and their families, and each will usually take several years to complete. However, such studies are very important, since there is no point in looking for genes that affect a disease if we know that genes are not important. It is only after this information is available and genes are known to be important that the next step can be taken.

Can enough families with enough affected members be found to help study the disease? Depending on the disease, the type of family that can be found for genetic studies may differ a lot. For diseases caused by a mutation in a single gene, families with many affected people can be found. Sometimes these families may have as many as twenty or thirty affected people, over three or four generations. These types of families are usually quite rare, and thus it can take a lot of work to find them. On the other hand, having even a single large family can be enough to allow a gene to be found.

For diseases where genes may have only a moderate effect, smaller families, where only two or three people (usually brothers and sisters) are affected, may be the only ones that can be found. Since such diseases tend to be more common in the general population, it is easier to find these families than to find the very large families. However, the smaller families cannot, by themselves, help much in finding the location of a disease gene. Therefore many such families (usually hundreds) are needed. How the actual process of finding the genes is done depends on the type of families that are studied.

One of the important aspects of finding the families is deciding how to ask them to be part of the study. It is important that each person who participates is told what he is going to have to do. In most cases, participants will just be answering a lot of questions, giving permission to get medical records about their disease, and giving a blood sample. Sometimes additional hospital tests might be needed. Before they can be studied, potential subjects must be asked to participate and must give "informed consent," which simply means that they have been told what they will need to do, what the risks (if any) are, and have agreed that this is fine with them. It is one of the overriding rules of human genetic studies that each person must volunteer for the study, that he gives informed consent, that he has the right to refuse, without the refusal affecting his medical care, and that he can withdraw from the study at any time.

What are the genes? Once the information and blood samples are collected from the families, the process of finding the genes can begin. There

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Understanding And Treating Autism

Understanding And Treating Autism

Whenever a doctor informs the parents that their child is suffering with Autism, the first & foremost question that is thrown over him is - How did it happen? How did my child get this disease? Well, there is no definite answer to what are the exact causes of Autism.

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