The Effect of Huntington's Disease on the Basal Nuclei: A Review

Huntington's disease is an autosomal dominant trinucleotide repeat disorder that causes the progressive degeneration of the basal nuclei. This degeneration leads to clinical symptoms affecting voluntary movement, cognitive impairment, and psychiatric disorders. The patient affected by this disease demonstrates anticipation, meaning that even though there is normal embryological development, the signs and symptoms appear at an earlier age as the gene is continually passed throughout subsequent generations. The degeneration occurs due to the accumulation of the protein Huntingtin that destroys the medium spiny neurons located in the caudate and putamen, collectively termed the striatum. Four pathways converge onto the striatum known as the "input" center. These consist of the motor loop, oculomotor loop, association loop, and limbic loop. In each of these loops, the striatum maintains an inhibitory gamma-aminobutyric acid (GABA)-ergic function. The imbalance of the inhibitory versus excitatory input directly relates to the symptoms seen in Huntington's disease such as the inability to control voluntary movements termed chorea, the inability to control voluntary saccadic ocular movements, the cognitive inability to plan and determine the direction of movement, and the inability to control the emotional and motivational aspects of the movement. There is currently no cure for Huntington's disease but there is a symptomatic treatment for the chorea and psychiatric conditions. Further research is being done to determine the pathophysiology behind the Hungtintin protein to allow for a targeted treatment regimen while also looking into reliable biomarkers for the progression of Huntington's disease.