Huntington Disease l: Introduction

Huntington disease is a progressive, autosomal dominant neurodegenerative disorder caused by the expansion of CAG trinucleotide repeats in the HTT gene on the short arm of chromosome 4, in which a three-base DNA sequence is abnormally repeated multiple times.

This repeat expansion leads to the formation of an abnormal huntingtin protein that disrupts normal cellular function.

The disease presents with a triad of motor, cognitive, and psychiatric symptoms. Motor signs include involuntary jerky movements called chorea, slow writhing motions known as athetosis, and sustained muscle contractions called dystonia.

In juvenile-onset cases, often linked to genetic anticipation, symptoms resemble Parkinsonism, including bradykinesia, rigidity, and tremor. As the disease progresses, voluntary motor control declines, leading to slurred speech, difficulty swallowing, and poor coordination.

Cognitive symptoms gradually progress to dementia, while psychiatric features include depression, anxiety, and obsessive-compulsive behaviors.