How can dna sequencing be used to identify genetic risk for certain diseases and disorders?

Scientists have sequenced the whole human genome; this means that the normal DNA sequence for the whole of human body is known. Thus, it is now possible to known the specific abnormalities that occur in disease conditions.
This means that people that are at risk of certain diseases can be tested by taking DNA sample from them and then comparing the sequence of their DNA with that of the diseased DNA sequence. 
For instance, pregnant women that are at risk of giving birth to children with down syndrome can be tested in the hospital to find out if the baby inside them have the disorder. This is done by collecting some amniotic fluid from their body, the fluid is then analyse for DNA sequence. If the fetus has down syndrome the pregnancy will be aborted.