Choose a Trait or Disease:

Scientists first decide what they want to study, like diabetes, cancer, height, or eye color.

Collect DNA Samples:

They collect DNA from two groups of people:

• Cases: People who have the disease or trait.
• Controls: People who do not have the disease or trait.

Genotyping:

Scientists use machines to scan each person’s DNA.

They look at hundreds of thousands, sometimes millions, of tiny DNA differences called SNPs (Single Nucleotide Polymorphisms).

Statistical Analysis:

Scientists compare how often each SNP appears in cases versus controls.

• If a SNP appears more often in people with the disease, it might be linked to the disease.

Identify Important SNPs:

If a SNP shows a strong connection to the disease, it could point to a gene that affects the disease.

Scientists wanted to understand why some people develop Type 2 Diabetes.

• They collected DNA from thousands of people with diabetes and thousands without diabetes.
• They scanned their DNA and found that people with certain changes near a gene called TCF7L2 had a higher risk of getting diabetes.
• This was an important discovery because TCF7L2 helps control blood sugar in the body.

Thanks to this GWAS:

• Scientists now understand more about how diabetes develops.
• New drugs are being studied that target the pathways involving TCF7L2.
• People can be tested for this genetic risk to help prevent diabetes earlier.

Find Disease Genes:

It helps find which genes are involved in diseases.

Better Treatments:

Understanding genes helps scientists create better and more targeted treatments.

Personalized Medicine:

Doctors can use a person’s genetic information to suggest better treatments or prevention methods.

Predict Risk:

It can help predict who might be more at risk for certain diseases.

• Breast Cancer:
• GWAS found DNA changes in genes like BRCA1 and BRCA2 linked to a high risk of breast cancer.
• Height:
• Many SNPs were found that help explain why some people are taller or shorter.
• Heart Disease:
• Scientists found several genes that raise the risk of heart attacks, helping create better medicines.

• Small Effects:
• Most DNA changes found by GWAS only slightly increase or decrease disease risk.
• Does Not Find Exact Cause:
• GWAS often finds areas near genes but not always the exact change causing the disease.
• Needs Many People:
• Big studies (with tens or hundreds of thousands of people) are needed for reliable results.
• Mostly European Data:
• Many early GWAS were done mostly with European populations, so results might not apply to all ethnic groups. Newer studies are trying to fix this.