Much of the content you need to cover for your presentation will be covered (briefly) in reference works, so they are a great place to start.
Before looking for primary literature use Reference Sources to get an overview or your topic.
Use these guides to find general information about genetic disorders. They can also help you to choose a genetic disorder for the assignment.
Once you know a little bit more about your topic, you could also use scholarly review articles to help you narrow down your topic or discover what is currently being researched. Here are a few examples of review articles about cystic fibrosis in cell biology scholarly journals. You can search for your own human disease by typing different keywords into the search box.
Nature cell biology journals - review articles about cystic fibrosis