Dentatorubral-pallidoluysian atrophy (DRPLA) is a genetic condition caused by a dominant allele of the ATN1 gene.
Explain what is meant by the term dominant allele.
The symptoms of DRPLA usually include progressive dementia, involuntary muscle spasms (chorea), and coordination problems. There is currently no cure.
Scientists have established that the severity and age of onset of DRPLA are related to the number of CAG trinucleotide repeats in the ATN1 gene.
People can undergo a genetic test to find out if they carry the mutated allele and the exact number of CAG repeats they have.
The graph below shows the relationship between the number of CAG repeats and the age at which symptoms first develop.
Discuss how useful the genetic test and the graph are for a person whose parent has been diagnosed with DRPLA.
A potential therapeutic approach involves using small interfering RNA (siRNA) molecules. These siRNA molecules bind specifically to the mRNA transcribed from the mutant ATN1 gene, triggering its enzymatic cleavage and degradation.
Explain how this drug could prevent or delay the onset of DRPLA symptoms.