I know the following article isn't related exclusively to infectious diseases, but it does somewhat pertain to the class because 1) we discussed chromosomes and genes last class, and 2) we know that there are viral agents of cancer.
As published in the latest edition of Nature, researchers have proposed a theory as to why people with Down syndrome rarely get cancer (people with Down syndrome are only about one-tenth as likely to get solid-tumor cancer as people without the syndrome). People with Down syndrome have an extra copy of chromosome 21 so instead of the usual two copies, they have three chromosomes. Chromosome 21 carries 231 genes including the RCAN1 gene which encodes a protein that suppresses the blood vessel growth needed for tumor growth. Scientists have theorized that the presence of an extra copy of this gene would result in more protein production and thus a possible anti-cancer effect.
The researchers from Harvard Medical School compared two sets of mice - one set had the extra RCAN1 gene while the other set had the normal pair. All mice were then surgically implanted with melanoma or lung tumors. Results showed that the set of mice with the additional protein had less than half as much tumor growth and fewer blood vessels surrounding those tumors as did the set of mice with the usual two genes. An analysis of human fetal tissues also showed that Down fetal tissues had nearly twice as much protein encoded by the RCAN1 gene as did normal tissues.
I know there are a lot of times when students get bogged down by the details of biology; we wonder why we have to memorize all the steps of the Krebs cycle or understand growth factor cascades. But articles like this always remind me that basic biology isn't just information restricted to a textbook; it has real implications, and understanding the biology of a disease facilitates opportunities for interventions.
For the complete journal article: http://www.nature.com/nature/journal/vaop/ncurrent/pdf/nature08062.pdf