Final answer:
CAG trinucleotide repeat diseases are characterized by the expansion of the CAG sequence in a gene, leading to protein misfolding and neuronal damage in various neurodegenerative disorders. DNA diagnostics can identify these expanded repeats, which typically affect gene expression and protein function.
Step-by-step explanation:
A characteristic molecular feature of CAG trinucleotide repeat diseases is the expansion of a specific trinucleotide sequence within a gene. These diseases, which can be classified as a group of biomarkers, are caused by an increased number of copies of the CAG codon sequence, leading to excessively long stretches of the same amino acid being produced. The build-up of these repeats affects the proper functioning of proteins and is associated with various neurodegenerative disorders.
For example, in Huntington's disease, the affected gene produces a protein with an abnormally long polyglutamine tract due to the expansion of CAG repeats. This alteration leads to protein misfolding and aggregation, ultimately causing neuronal cell damage and clinical symptoms of the disease. DNA diagnostic techniques can identify these expanded repeats, which are often found within the non-coding regions (introns) of the gene but can still influence gene expression and protein function.