Huntington’s is a progressive disease that is caused by mutations in the huntingtin (HTT) gene. Symptoms of the disease include movement disorders, psychiatric abnormalities, cognitive and behavioral issues, and problems with feeding and communication.
Symptoms related to movement in Huntington’s disease include chorea (involuntary jerking or writhing movements), dystonia (muscle problems, such as rigidity), slow or abnormal eye movement, abnormal gait, posture or balance, and difficulty in speech or swallowing.
Movement impairment earlier in the disease course includes slight uncontrollable movements of the face and jerking, flicking, or fidgety movements of the limbs and body. As the disease progresses, the involuntary movements tend to occur more often and become more extreme.
In more advanced disease states, this may change and the patient’s movements may become slower as the muscles become more rigid.
Cognitive and behavioral impairment
Cognitive and behavioral impairments in Huntington’s disease include difficulty in organizing, prioritizing, and focusing on tasks, lack of flexibility or a tendency to get stuck on a thought or behavior, lack of impulse control, lack of awareness of one’s own behavior, slowness in processing thoughts, and difficulty learning new information.
Huntington’s patients often show a lack of emotion and may not recognize the needs of others. Patients can also display aggression, excitement, apathy, anti-social behavior and anger. As the disease progresses, they may develop a lack of interest in hygiene and self-care.
Depression is the most common psychiatric disorder in patients with Huntington’s disease. This occurs due to injury to the brain and not simply as a reaction to receiving a diagnosis. Depression can cause patients to feel irritable, sad, or apathetic, experience social withdrawal, insomnia, and fatigue, and may have frequent thoughts of death or suicide.
Other psychiatric disorders that occur in Huntington’s patients include obsessive-compulsive disorder, a condition with recurrent, intrusive thoughts and repetitive behaviors.
Mania is another disorder associated with Huntington’s disease. It causes elevated mood, hyperactivity, impulsive behavior, and feelings of high self-esteem.
Patients with Huntington’s disease may also experience bipolar disorder, which is a condition with alternating episodes of depression and mania.
Weight loss is common in patients with Huntington’s disease, particularly as it progresses. Patients with the disease do have a good appetite. However, they can find eating tiring, frustrating, and messy as the muscles of the mouth and throat do not work properly due to the loss of muscle control. This can sometimes lead to choking and recurrent chest infections.
Patients with Huntington’s also tend to have communication problems as they have difficulty putting thoughts into words and slurred speech patterns. They understand what is being said, but may not be able to respond. As the disease progresses, patients can become less responsive and more withdrawn.
Variability in Huntington’s symptoms
Huntington’s disease can have a variable course depending on each patient. Most people experience symptoms in their 30s or 40s, but it can also occur earlier or later in life. This difference in age of onset has been found to be related to the mutation that causes Huntington’s, a CAG trinucleotide repeat extension in the HTT gene.
Healthy people have 35 or fewer CAG repeats in the HTT gene, while Huntington’s patients can have repeats ranging from 36 to 120. Many studies have suggested that the length of CAG repeats is correlated with the age of onset and severity of the symptoms; patients with fewer CAG repeats tend to have a later disease onset and milder symptoms compared to those with longer repeats.
The variability of symptoms experienced by people with Huntington’s disease has also been found to be correlated with the degeneration of different regions of the brain. For example, patients with mainly mood symptoms show a degeneration in regions of the brain called the striatum or the cerebral cortex, while patients with mainly motor symptoms tend to have marked degeneration in the primary motor cortex with some degeneration in the striatum.
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