Huntington’s Disease

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Frontal Lobe.

Frontal Lobe

The frontal lobe is located at the front of the brain and is important for our, ability to communicate, primary motor function (i.e. our ability to consciously move our muscles), emotional expression, speech, problem solving, memory, language, judgment and social interactions (making social decisions, knowing when to do things, suppressing impulses)

Brain image with basal-ganglia highlighted.

Basal Ganglia and Huntington’s Disease

The basal ganglia are located deep in the brain and control voluntary movements, affects spatial awareness, balance and coordination, and our ability to move on from a thought or task as well as prioritising tasks.   Memory formation and storage as well as complex emotional responses are also controlled from this region. The basal ganglia have strong connections to the frontal lobes and damage to the basal ganglia can also lead to impaired functioning of the frontal lobes.

Every one of us carries the Huntingtin gene, which assists nerve cells in functioning effectively. For those with HD, their HD gene is faulty which causes the symptoms of HD. This disease does not discriminate between race, gender, ethnicity and age. Whilst HD might not be well known within the wider community, it is not as rare as most people think. In fact, it could affect someone you know.

What is HD?

Huntington’s Disease (HD) is caused by an expansion of the Huntingtin gene which results in brain cell death. The regions of the brain affected are the basal ganglia and frontal lobe. These regions are responsible for motor movement control and coordination, cognition, personality and emotions. Deterioration in these regions of the brain results in significant impairments in one’s ability to think, feel and move. Whilst people are born with a faulty copy of the gene, they do not have HD at birth, but rather onset predominantly occurs in young-middle adulthood (35– 50years). There is a juvenile form of Huntington’s disease (JHD) that presents before the age of 20 and, although rare, it is more rapidly progressive.

The Genetics of HD

We all have a huntingtin gene. It is located on chromosome 4 which means that it is not linked to our gender – both men and women can be affected equally. When a child is conceived, it inherits half of its DNA from mum and the other half from dad. If they have a parent with HD, they could inherit either a healthy HD gene or the faulty HD gene. If they inherit the faulty copy this means that at some point in their life they will also develop the symptoms of HD. However, if they inherit a healthy (normal) copy of the gene from the parent with HD, this means that they will not develop HD nor pass it on to future generations.

Who is affected?

Being a genetic disease, each child of an affected parent has a 50% chance of inheriting the faulty Huntingtin gene. HD both directly and indirectly affects the following:

  • Diagnosed with Huntington’s disease – this is someone who has been formally diagnosed and is showing symptoms (symptomatic) of HD.
  • Tested gene positive after predictive testing – this is someone who is not symptomatic but will eventually develop symptoms of HD as they have inherited the faulty gene from their affected parent.
  • At-risk of developing Huntington’s disease – this is someone with a parent who has HD but has not had gene testing themselves.   This person is unaware if they have two ‘working copies’ of the HD gene or if they have inherited one ‘faulty copy’.
  • Tested gene negative after predictive testing – this is someone who has been tested and does not carry the faulty gene. This person has two ‘working copies’ of the gene. They are considered to be genetically not at risk and will not develop symptoms of HD.
  • Carers of persons identified above
  • Symptomatic- this is a person who is displaying symptoms of HD but have not been formally diagnosed by a HD specialist

Symptoms

The onset of symptoms typically occurs in middle adulthood (35-50 yrs of age) but may develop at any age. There is no specific order or sequence in which the symptoms present and they can vary between individuals and family members. For example some people may have significantly impaired movements and balance but may only be experiencing minor cognitive impairment.

Physical

HD is most widely known for its physical symptoms, specifically the jerky involuntary movements also known as chorea. However for individuals suffering from HD, they may experience physical symptoms other than involuntary movements and can include the following:

  • Involuntary movements
  • Impaired balance & coordination
  • Swallowing difficulties
  • Slurred speech & impaired communication

Emotional / Psychological

HD affects the regions of the brain responsible for our emotions and personality. Degeneration of brain cells in these regions can lead to a person displaying a range of different emotional disorders and/or personality changes. These changes can initially be subtle and become more prominent as the disease progresses. HD can affect normal responses to everyday situations. Some of the following psychological changes might be experienced:

  • Depression & anxiety
  • Obsessive compulsive behaviour
  •  Psychosis
  • Personality changes

Cognitive

Different to the physical symptoms, cognitive symptoms are harder to identify without a formal cognitive assessment. Like with some of the emotional symptoms, cognitive changes can be subtle at first and have a limited impact on a persons’ independence and daily activities. However, as the disease progresses, HD progressively impairs cognitive function which can result in the following:

  • Memory difficulties
  • Impaired thinking, planning & organising tasks
  • Rigidity in thought patterns
  • Impulsive & disinhibited behaviours
  • Perseveration (a fixation on a thought, idea or feeling)

‘Symptom Watching’

The practice of ‘symptom watching’ is common. Symptom watching occurs when people are carefully noting all their actions and behaviours and associating them with symptoms of HD. Symptom watching is a natural and understandable response to being at risk or gene positive. Many of the symptoms of HD such as fumbling, moodiness or forgetfulness are also experienced by the general population not at risk of HD. Symptom watching is a normal response to having HD in your family. However, if you feel that it is having a negative impact on your life, it’s important to seek professional advice from someone you trust for example your GP, psychologist or counsellor, HD specialist, Huntington’s Victoria.