Huntington’s disease is a hereditary and progressive neurodegenerative disease characterized by uncontrolled movement, mental instability, and loss of cognitive function. It can be divided into five stages of disease progression.
Stage 1: Early stage
The early stage starts at disease onset and lasts for approximately eight years. During the early stage, the patient already has been diagnosed with Huntington’s disease, but is fully functional at home and at work. He or she usually maintains typical pre-disease levels of independence when it comes to everyday activities such as finances, home responsibilities, and activities of daily living, which include eating, dressing, bathing, etc. At this stage, patients typically do not experience impaired motor symptoms, but may experience mild cognitive symptoms and psychiatric changes.
Stage 2: Early intermediate stage
The early intermediate stage of Huntington’s can last between three and 13 years from disease onset. In the early intermediate stage, the patient is still functional at work, but at a lower capacity. He or she is mostly able to carry out daily activities despite some difficulties and usually requires only slight assistance with daily functions.
At this stage, the patient also may be unable to work and require major assistance in one basic function, while other basic functions are carried out independently. Chorea, which is irregular involuntary movement in multiple areas of the body, may develop at this stage.
Stage 3: Late intermediate stage
The late intermediate stage lasts between five and 16 years from disease onset. In this stage, the patient no longer can conduct work or manage household responsibilities. He or she will require substantial help for daily financial affairs, domestic responsibilities, and activities of daily living. The patient’s ability to think also may become more impaired. Psychiatric and behavioral symptoms, including irritability, anxiety, and impulsiveness may become evident. In general, cognitive, psychiatric, and motor features worsen at this stage.
Stage 4: Early advanced stage
The early advanced stage lasts between nine and 21 years from disease onset. The patient is not independent at this stage, but still can reside in their home with help from either family or professionals, although their needs may be better met at an extended care facility. The patient will require substantial assistance in financial affairs, domestic responsibilities, and most activities of daily living. He or she will be aware of which activities have to be done, but will require major assistance to act on them.
Stage 5: Advanced stage
The advanced stage lasts between 11 and 26 years from disease onset. Patients with Huntington’s disease at the advanced stage need total support in daily activities from professional nursing care. Chorea lessens at this stage, but Parkinsonism increases, which includes slowness, stiffness, teeth grinding, and abnormal limb postures. The ability to walk and maintain an upright posture also worsens and there is an increased incidence of falls. Speech can become difficult at this stage and the patient may go through periods of confusion and screaming. The ability to swallow also can worsen, and there can be extreme fluctuations in blood pressure and temperature.
Patients with Huntington’s disease usually die 15-20 years after the symptoms first appear. The cause of death usually is a complication of Huntington’s, such as pneumonia, heart failure, or infection.
Variability in disease severity and progression
It is thought that the variability in disease severity and rate of progression among people with Huntington’s is linked to the genetic mutation causing the disease. Huntington’s is caused by a mutation in the HTT gene. This mutation is in the form of a CAG trinucleotide repeat expansion. Although the exact reason for this is unknown, multiple studies have suggested that the number of the CAG repeats is inversely correlated with the age of onset of the symptoms and disease severity; patients with fewer CAG repeats showing the symptoms of the disease when they are older have a slower disease progression and reduced symptom severity.
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