Searching among all of our 20,000 or so genes for a few that are involved in a complex disease can be quite costly and time consuming. That is why researchers often use what they and others know about a disease to narrow their focus down to a smaller number of "candidate genes".

A smart way to start narrowing down the number of candidate genes is by looking at what we already know. As part of the scientific process, researchers routinely publish their discoveries in journals. Other researchers read the journal articles and then build on these past discoveries.

Protein biochemist - Studies protein structure and function, and how proteins interact with one another. Provides a basic understanding of the problem.

Clinician - Treats patients for nicotine addiction. Provides access to patients and collects DNA samples from nicotine addicts and their family members.

DNA Analyst - Can rapidly analyze the DNA sequence from hundreds of blood samples. Analyzes and compares the DNA sequences of nicotine addicts and non-addicts.

Researchers often work together, or collaborate, to tackle a problem from several angles at once. This allows researchers to pool their areas of expertise to everyone's benefit.

In order to determine whether a gene is associated with nicotine addiction, a protein biochemist might need to collaborate with both a clinician and a DNA analyst.

How can a difference in someone's gene sequence cause a behavioral change, like being more susceptible to nicotine addiction?

After collecting DNA from several people with nicotine addiction and ADHD, you analyze their CHRNA4 gene sequences to determine which alleles they carry.

Upon comparing addicts with ADHD to non-addicts and addicts without ADHD, you determine that allele 2 seems to be significantly more common in addicts with ADHD.

However, not everyone who has allele 2 is addicted, and not everyone who is addicted has allele 2. Clearly, there is more to this story than this one gene. Such is the nature of complex diseases. Nicotine addiction and ADHD are complex diseases affected by many genes and environmental factors.

CHRNA4 is just one gene that may play a role in addiction. The next step is to identify other addiction genes and determine how they work together to produce this complex disease.

Understanding these genes' roles and how they interact can help lead to more effective treatments for nicotine addiction.