Donate
Huntington’s disease (HD) is a progressive, genetic neuropsychiatric
disorder that causes the dysfunctioning and/or death of neurons (nerve
cells) in the brain. As a result, a gradual decline in the physical and
mental abilities occurs overtime generally during the middle age years
(though the age at onset is variable from 1-70 years). Every child of a
patient with HD usually has a 50% chance of inheriting the disease. This
does not mean 50% of all the children of a patient will be affected. For
each child, it is same as the chance of getting a head or a tail when you
flip a coin. It is not dependent on the gender of the person. Both genders
are equally at risk.
Symptoms usually appear between the ages of 30 to 50 years, and worsen over
a period of 10 to 20 years as per the reports from the western countries. The
situation is different in India where the awareness is less and treatment options
are largely inaccessible.
There are broadly 3 domains that are affected.
1) Motor,
2) behavioural (psychiatric),
3) intellectual (cognition)
Dancing like movements (chorea), posturing of body parts (dystonia), tightness in the body (rigidity), slowness (bradykinesia), swallowing difficulty (dysphagia), unclear speech (dysarthria) etc.
Personality changes such as uncontrollable anger, emotional lability,
apathy, mood swings/depression, anxiety, obsessive thoughts,
repetitive/compulsive behaviour, suspiciousness, fear of harm etc.
Caution: Behavioural symptoms can be overrated in at risk individuals.
Unless the symptoms cause disruption in daily life and functionality, it is
not advisable to attribute them to HD.
Forgetfulness, lack of attention, verbal deficits, impaired judgment, disinhibited behaviour or lacking social awareness
Sleep and circadian rhythm disturbances, weight loss, hypothyroidism and
Diabetes Mellitus.
Not every patient have all the above features but
most of them have more than one domain affected. More the number of features,
stronger the suspicion of HD.
The mutation that causes the disease is the abnormal length of a repeat sequence (CAG) in the Huntingtin (HTT) gene which is named after George Huntington. The repeat sequence when crosses a threshold of 35 can cause HD but not in every case. CAG repeat >/40 causes HD in almost all cases (fully penetrant). This abnormal length of CAG results in a faulty protein that is sticky and becomes the garbage inside the neuron (nerve cell) apparently causing its malfunction and death. The more CAG repeats one has, the earlier the disease kicks in. Why and how this happens due to long CAG repeats is not fully understood but probably is due to the increased stickiness among several other factors.
Unlike many neurological conditions which rely on probabilistic diagnostic tests, HD has a definitive diagnosis through a genetic test that measures the CAG repeats in the HTT gene. Also, the test result is not just a categorical positive or negative but puts patients on a continuum of outcomes based on the number of repeats. While CAG repeat is not the only determinant of disease outcome, it is the definitive marker of the occurrence of HD.
HD has no complete cure. It means one cannot effectively stop the neurons to die with the existing treatments but the symptoms are treatable. Chorea (dancing movements) can be effectively treated with drugs like Tetrabenazine and several psychiatric drugs immensely benefit the patients suffering from anxiety, depression, psychosis, OCD etc. Besides pills, many rehabilitation measures such as speech therapy, swallowing therapy, physiotherapy, counselling are very helpful. These things can greatly increase the quality of life and one should not be discouraged to see a doctor and be on follow up because of the lack of complete cure.
The course of HD with respect to age at onset and progression is drastically variable from individual to individual. The description here applies to majority of the cases but not all. Though often patients present to a neurologist with choriform movements as the presenting symptom, there can be subtle or gross personality changes and psychiatric disturbances before the motor onset which are ignored by majority of the patients. Hence chorea forms the hallmark of the disease. In certain cases, the psychiatric disturbances are so severe before the onset of chorea that they present to psychiatrist and HD may skip the consideration if they do not reveal the family history of movement disorder. In the early phases of chorea, the movements are subtle, often appearing as semi-purposeful such as brushing the hair with the hand. These kind of stereotypical or repetitive movements are seen in many diseases and sometimes with no disease. It may start in one body part and gradually involve many body parts and be generalized. Symptoms occur based on the parts involved e.g. walking disturbances when lower limbs and trunk are affected, difficulty in speech when muscles in and around mouth are affected, breathing difficulty when the chest muscles are affected etc. In this middle phase, one or more of these symptoms start appearing along with inattention. Many people are partially dependent on care takers for daily activates. It is important for the caretakers to let the affected individuals be independent otherwise the disease symptoms aggravate and the abilities diminish over time. Simultaneous to the movement disorder, patients experience varied behavioural symptoms and impaired intellectual capacity to varied extent. It can also result in loss of job as seen in most cases. In later stages, the symptoms worsen to the extent of full dependence on the caretaker for daily activates and become totally dysfunctional. Frequent choking, frequent falls, breathing difficulty and severe weight loss are the hallmarks of the late stage. HD is not fatal by itself and major causes of death include choking resulting in aspiration pneumonia and falls resulting in intracranial bleeds. In all stages of HD, weight loss can be an important complication that can correspond with worsening symptoms and should be countered by adjusting the diet and maintaining appetite.
Every child of a parent with HD has a 50/50 chance of inheriting the expanded gene that causes the disease. If the child has not inherited this expanded gene, he or she will never develop the disease and cannot pass it on to their children i.e. HD will not skip a generation and reappear in the lineage. In case if there is no parent affected and it is a new mutation, then the siblings of such patient could be considered as at risk even if the parents are normal. The children of at risk individuals can be considered at risk but the direct risk can be established only if the parent shows symptoms. It is recommended that unless there is an affected parent or sibling, there should not be any worry for the grossly uncertain and remote possibilities.