Chapter 21, Problem 20P

Interpretation Introduction

Interpretation:

The evidence to support the generational increase in the number of CAG repeats should be described.

Concept introduction:

Huntington's disease is a neurodegenerative disorder dominantly transmitted having a variation in age of occurrence having an average age of $\text{40}$ years. Huntington's disease is a disorder of tri nucleotide repeat caused due to an increase in the number of repeats of the CAG sequence in HD gene. Repeats ranging around $\text{40}$ or more are linked with expression of disease, whereas repeats having $\text{26}$ and less in number are normal. Repeats having numbers between these are not linked with the disease expression but might cause expansion in transmission paternally resulting to the disease in offspring. The disease is progressive from generation to generation which means in later generations the number of CAG repeats increases and age of onset of symptoms decreases.