Neurodegenerative Diseases

August 13, 2020 Rima Medical Science 0

What are neurodegenerative diseases?

  • Neurons are the building blocks of our nervous system which consist of brain and spinal cord. Our brain is complex organ with vast number of pathways, which control our thoughts, emotions, our ability to reason and communicate with the outside world.
  • Neurons communicate with each other to perform every function of the brain. Neurons normally don’t reproduce or replace themselves, so when they are damaged or die, they cannot be replaced by body.
  • Neurodegenerative disease is an umbrella term used for a range of conditions which primarily affects the neurons in the human brain. They are among the most complicated disease that affects the brain. Neurodegeneration is the progressive loss of structure and function of neurons, including death of neurons.
  • Neurodegenerative diseases cause our brain and nerves to deteriorate over time. They can affect our mental activities, change our personality, cause confusion and affect movement.
  • There is no cure for any neurodegenerative disease till date. The treatment available provide only symptomatic care and slows progression of disease.

Some common neurodegenerative diseases are:

  • Alzheimer’s Disease.
  • Parkinson’s Disease.
  • Huntington’s Disease.
  • ALS (Amyotrophic Lateral Sclerosis)

Alzheimer’s Disease

  • It is the most common neurodegenerative disease in the world and is the most common cause of dementia- continuous decline in thinking, behavioral and social skills. It is one of the top 10 leading cause of death in the United States.
  • The main symptom of Alzheimer’s disease is memory loss which persists and worsen over time affecting the ability to function at work or home. The patient with Alzheimer may repeat statement or questions, get lost in familiar places, forget the name of family members or common objects and have difficulty in concentration and thinking. It also affects the ability to make reasonable judgement and decisions (wearing summer clothes in winter) and to perform familiar tasks like cooking or playing game.
  • Pathologically, it is characterized by intracellular neurofibrillary tangles and extracellular amyloid plaques.
  • Its exact cause is not understood till date. It is caused by combination of genetic, environmental and lifestyle factors. The risk factors include increasing age, sex (women are at greater risk than men), family history and genetics (more risk with AD affected mother than father), presence of cardiovascular disease, history of head injury and poor sleep patterns.
  • Currently available treatment includes acetylcholinesterase inhibitors (rivastigmine), NMDA receptor antagonist (memantine), . These drugs slows the progression of disease and provide symptomatic relief but fail to achieve a definite cure.
  • Many researches are ongoing to know about unrevealed aspects of Alzheimer’s disease.

Parkinson’s Disease (PD)

  • It is a neurodegenerative disorder which mostly affect the motor activities. The signs and symptoms may vary. The common signs and symptoms include motor symptoms which are tremor which usually begins in a limb, bradykinesia (slow movement), slurred speech, stiff and rigid muscles, gait and balance problems. Non-motor symptoms include depression, cognitive impairment and sleep behavior disorders. These non-motor symptoms become troublesome in later stages of PD.
  • Most of the symptoms occur due to death of neurons producing chemical messenger called dopamine. Decreased dopamine level causes abnormal brain activity leading to impaired movement and other symptoms of Parkinson’s disease.
  • The presence of lewy bodies (accumulation of abnormal alpha-synuclein) in substantia nigra neurons of PD patients is topic of interest among researchers.
  • Risk factors include age, heredity and sex. PD usually begins at the age of about 60. However, some individuals may have ‘early-onset PD’ which usually begins before age 50. Men are more prone to develop PD than women.
  • Treatment strategy involves pharmacological approaches (mainly with levodopa preparations with or without dopamine agonist, MAO-B inhibitor) and non-pharmacological approaches (exercise, physical, occupational and speech therapies).

Huntington’s Disease

  • It is also known as Huntington’s chorea and is a rare, inherited, neurodegenerative disorder characterized by unwanted choreatic movements, dementia and behavioral and psychiatric disturbances.
  • The symptoms generally start between the age of 30s or 40s. In some cases, the symptoms start before age 20 and is known as Juvenile Huntington’s Disease of JHD. The movement disorders associated includes chorea (involuntary jerking or writhing movements), slow or abnormal eye movements, impaired posture and difficulty in speech or swallowing. Cognitive disorders include lack of impulse control, difficulty in learning new information, lack of focus on tasks and slowness in processing thoughts. Psychiatric disorder associated are depression, mania or bipolar disorder.
  • The starting symptoms in JHD may be slightly different and include difficulty in paying attention, drop in school performance, seizures, frequent falls, contracted and rigid muscle.
  • Common cause of death include pneumonia or other infections, injury due to falls and complications due to difficulty in swallowing.
  • It is caused by mutation in the HTT gene which is involved in giving instructions for making a protein called huntingtin. The exact function of this protein is unclear. In normal HTT gene, the CAG segment is repeated about 10-35 times whereas in people with HD, it may repeat from 36 to over 120 times. Those with greater than 39 CAG repeats are certain to develop the disease while people with 36-39 repeats may or may not develop it.
  • It is inherited in an autosomal dominant matter which means having a change in only of 2 copies of HTT gene is enough to cause the disease.
  • Its management is based on treating symptoms to improve quality of life.

Amyotrophic Lateral sclerosis (ALS)

  • ALS is also called Lou Gehrig’s disease after a baseball player who was diagnosed with it. It causes deterioration of motor neurons leading to their death.
  • It primarily affects the upper and lower motor neurons leading to motor and extra-motor symptoms. Early symptoms include muscle twitching, cramping, weakness, slurred speech and difficulty in speech or swallowing. As the disease progresses, people become weaker and are eventually wheel-chair dependent. Death may result from respiratory failure.
  • There are various types of ALS, distinguished by symptoms. It may be familial (inherited) or sporadic (not inherited). About 90-95 % cases are not inherited.
  • The FDA approved treatment are riluzole and endaravone. Other treatments help to relieve symptoms and improve quality of life.

How we can prevent neurodegenerative diseases?

Though we cannot completely prevent occurrence neurodegenerative diseases, we can follow some tips which help us to prevent or delay symptoms of these diseases. Some important tips include:

  • Eating foods rich in different kind of nutrients like omega-3 fatty acids, folate, choline, vitamin B-12 and vitamin E.
  • Regular physical activity help to protect against dementia ad PD.
  • Being involved in cognitive activities like chess, play word puzzle, playing an instrument etc.
  • Meditation can help improve cognition and memory.

References

  1. https://www.mayoclinic.org/diseases-conditions/alzheimers-disease/symptoms-causes/syc-20350447
  2. https://rarediseases.info.nih.gov/diseases/6677/huntington-disease
  3. https://rarediseases.info.nih.gov/diseases/5786/amyotrophic-lateral-sclerosis
  4. https://www.niehs.nih.gov/research/supported/health/neurodegenerative/index.cfm
  5. Kumar a, Ekavali AS. A review on Alzheimer’s disease pathophysiology and its management: an update. Pharmacological Reports. 2015; 67(2): 195-203.
  6. Khanahmadi M, Farhud DD, Malmir M. Genetic of Alzheimer’s Disease: A Narrative Review Article. Iran J Public Health. 2015; 44(7): 892–901.
  7. Armstrong MJ, Okun MS. Diagnosis and Treatment of Parkinson Disease: A Review. JAMA. 2020; 323(6): 548-560.
  8. Radhakrishnan DM, Goyal V. Parkinson’s disease: A Review. Neurology India. 2018; 66(7): 26-35.
  9. Hardiman O, Al-Chalabi A, Chio A, Corr EM, Logroscino G, Robberecht W et al. Amyotrophic lateral sclerosis. Nature Reviews Disease Primers. 2017; 3(17071).