Huntington’s Disease (HD) is a genetically transferred, progressive neurodegenerative disease that is caused by a defect on chromosome 4. The chromosomal defect is inherited through an autosomal dominant gene and causes a cytosine-adenenine-guanine (CAG) repeat to occur more often than expected. This codes for an abnormality in the protein huntingtin. When huntingtin has mutated, cells are not able to carry out their functions, leading to neuronal death(1). This death causes motor, psychiatric and cognitive abnormalities, which completes the triad of symptoms that are typical of HD.
HD has characteristic signs and symptoms that form a stereotypical clinical presentation. The typical with HD is of European descent and between 30-50 years old. Symptoms are divided into three categories: motor, psychiatric and cognitive. The motor abnormalities, or chorea, fall onto a spectrum of severity. Initially, they may consist of small restless movements. Eventually, involuntary choreoathetoid movements of the extremities, head and face are apparent. These movements are the hallmark of HD and lead to extreme disability.
While the chorea may be the most striking feature of HD, psychiatric and behavioral disturbances are generally the first to present, occurring decades before movement abnormalities are noted(2). These consist of depression, anxiety, irritability and extreme anger. Psychotic disturbances can also be problematic for these patients.
Cognitive decline will also affect patients with HD. They experience defects in memory, judgment and reasoning along with a decreased ability to plan and organize. Studies have shown that tracking motor planning/speed and sensory-perceptual processing are the best indicators of a patient’s cognitive ability, particularly when a patient is pre-diagnosis(3). As the cognitive abilities decline, dementia will set in and continue to progress.
DIAGNOSIS AND EVALUATION
Diagnosis and evaluation of HD can be accomplished through symptomatic diagnosis, imaging studies and genetic evaluation. Symptomatic diagnosis is made by the combination of motor, psychiatric and cognitive abnormalities discussed previously. For those portraying abnormalities consistent with HD, questionnaires such as the Symptom Checklist 90 Revised (SCL-90-R) can be helpful. The SCL-90-R is completed by the patient and is designed to evaluate all components of HD(4). Other scales such as the Unified Huntington’s Disease Rating Scale (UHDRS) and the HD-specific Quality of Life Instrument (H-QoL-I)(7) can also help to evaluate functioning, severity and treatment effectiveness. The PREDICT-HD study suggests that considering all potential factors and taking a multidimensional approach for those at risk for HD can lead to treatment initiation before significant functional deterioration(5).
Neuroimaging studies are used to diagnose and evaluate the rate of neurodegeneration. A CT may show loss of...