Chapter 21, Problem 8P

Interpretation Introduction

Interpretation:

Huntington's disease is an inherited neurological ailment with a variable age of onset. A protein called huntingtin has a sequence of repeated glutamine residues, all encoded by CAG. The number of repeated CAG triplets is expanded in Huntington's disease, apparently as the result of replication errors. The age of onset is related to the number of CAG triplets in the repeat region; the more glutamine codons, the earlier the onset. The experimental evidence, using Southern blotting, that is consistent with this finding should be explained.

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. The children of the parents who are Huntington's disease carriers of the gene have a chance to inherit the disease by $\text{50\%}$.

The symptoms of the disease include cognitive impairment, mood disorders and behavioral changes which are chronic in nature and progress with the course of time and illness. Huntington's disease is a disorder of trinucleotide 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.