What Are Neurodegenerative Diseases?

Neurodegenerative Diseases are classified as a group of disorders that affect the health of the nervous system, majorly focusing on the Central Nervous System (the brain and the spinal cord). Such diseases are characterized by the degradation and death of neuronal cells- the building blocks of the body’s nervous system-, causing a loss of normal brain function.

Neurodegeneration affects millions of people around the world, with the elderly generation as the primary demographic. Most neurodegenerative diseases do not have a cure. However, treatment for symptom management and disease progression is available. As the population ages, more attention is being paid to neurodegenerative conditions nowadays compared to decades ago; this is leading to a deeper understanding and differentiation of neurodegenerative diseases, resulting in better patient care.

Overview

Neurodegenerative Diseases affect millions of people globally; these conditions primarily affect the elderly population, increasing the requirement for personal care as neuronal degeneration progressively affects quality of life. Some neurodegenerative diseases are cognitive-related, affecting mainly psychological and mental activity, whereas others are motor-neurons-related, resulting in involuntary movements and tremors.¹

What are neurodegenerative diseases?

Neurodegenerative disorders are characterized by the decreased function or cell death of neurons, which are the primary building blocks of the nervous system. Areas of the brain are often affected, and, as the disease progresses, there is a high degree of brain neuron cell death, which is required for the normal function of the Central Nervous System (CNS).¹

What are the symptoms of neurodegenerative disease?

Some of the most common symptoms associated with neurodegenerative disease include:

• Decreased cognitive function (e.g. thinking, learning, reasoning)
• Dementia
• Behavior alterations
• Motor dysfunction 

Neurodegenerative Diseases affect the CNS, which includes the brain and the spinal cord.The anatomical structures that are most frequently affected by these diseases are found in the brain:²

• Hippocampus (linked to long-term memory)
• Limbic system (related to behavior and emotions)
• Entorhinal cortex (linked to memory)

Neurodegenerative diseases can be split into two major groups, depending on the corresponding clinical signs and symptoms observed in the patient:²

• Cognitive dysfunction- e.g. Alzheimer's Disease
• Motor Dysfunction- e.g. Parkinson's Disease

The anatomical structures of the brain and spinal cord affected in motor dysfunction neurodegenerative disorders are:

• Basal ganglia
• Brainstem nuclei
• Cerebral cortex
• Lower motor neurons of the spinal cord
• Thalamus

What is the most common neurodegenerative disease?

The most common neurodegenerative diseases are:

• Alzheimer's Disease
• Parkinson's Disease
• Amyotrophic Lateral Sclerosis (ALS)

Alzheimer's disease

Alzheimer's Disease (AD) is a neurological disorder that affects the integrity of the brain, and results in a massive decrease in brain volume due to the accelerated death of neurons. This leads to memory loss and is a primary cause of dementia- accounting for up to 50-75% of cases.³

Causes

Up to 70% of AD cases are associated with genetic traits, whereas the other 30% are attributed to environmental factors. Genetic traits include mutations in one or more of the major genes currently associated with this disease, such as: PSEN1, PSEN2, APOE, and APP.  The main cause of AD is thought to be the accumulation of misfolded amyloid proteins (called amyloid plaques), which are caused by a mutation in the APP gene.³

Types of AD

• Familial AD- there is a family history of AD in ~0.5% of all cases. Onset happens usually earlier than in sporadic AD, at around 30-50 years of age
• Sporadic AD- the most common form of AD. There is no genetic link found so far

Clinical traits

The major trait of AD is the presence of amyloid plaques and neurofibrillary tangles (NFTs). These are anatomical traits in the brain, formed by the accumulations of misfolded proteins, associated with AD.

Diagnosis

AD is diagnosed upon clinical assessment of its principal symptoms, such as cognitive impairment. Some of the techniques used for the detection and diagnosis of AD are:

• Blood tests- these are related to cognitive function and include full blood count (FBC), renal function, thyroid function, and vitamin B12/folate levels.
• Magnetic Resonance Imaging (MRI) of the brain
• Positron Emission Tomography (PET) imaging 
• Genetic Testing

Treatment

There is no cure for AD. However, treatment options usually try to target symptoms and prevent further progression of the disease. Treatment is also targeted at different stages. Some of the medications used for AD are:

• Acetyl-cholinesterase inhibitors (AChEIs) (donepezil, galantamine, and rivastigmine)
• Memantine 

Parkinson's disease

Parkinson's Disease (PD) is a neurodegenerative disorder characterized by motor dysfunction and involuntary movement. PD affects around 1-2% of the population over the age of 50.⁴

Symptoms

• Resting Tremors
• Bradykinesia (slow movement and speed)
• Cognitive impairment

Types of PD

• Familial PD - ~10% of cases are linked to genetic inheritance
• Sporadic PD- ~90% of PD cases are of unknown origin

Causes

Genetic and Environmental causes or both

Diagnosis

Diagnosis is usually given upon clinical examination and signs and symptoms evaluation by a professional. Some signs that are crucial for PD diagnosis include:⁵

• Resting tremors
• Bradykinesia (slowness of  movement)
• Reduced olfaction (sense of smell)
• Postural instability 
• Micrographia (abnormally small and cramped handwriting)

Treatment

Although there is no cure for Parkinson's Disease, there are options for treatment that could help patients with motor dysfunction associated with PD. Current medication includes:

• Levodopa- the most commonly prescribed treatment and a precursor to the dopamine neurotransmitter that motor cells use to function. Long-term use can provoke motor complications and dyskinesia (involuntary movements of the face, trunk, legs, or arms)
• Dopamine agonists- shown to prevent motor complications from starting too soon. These treatments are usually less effective than Levodopa

If Levodopa is used as the initial treatment of PD and side effects (such as dyskinesia) are experienced, the administration of additional medication such as dopamine agonists, catechol0-methyltransferase inhibitors, and monoamine oxidase- B inhibitors is suggested.

Amyotrophic lateral sclerosis (ALS)

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease associated with high risk of mortality. ALS is associated with quick progression since approximately 50% of patients die within 30 months of diagnosis, and 20% survive for 5-10 years after the onset of symptoms.⁶ The incidence of ALS is 5.4/100,000 in Europe and 3.4/100,000 in North America.⁷

Causes 

Causes of ALS could be both environmental and genetic factors. 

• Familial ALS- Approximately 5-10% of cases are due to genetic factors. It is caused by inherited mutations in different genes: SOD1, TARDBP, FUS
• Sporadic ALS- Men are at higher risk of developing ALS (1:350) than women (1:400)

Clinical traits

The average age of ALS onset is 58-63 years for sporadic ALS, and 47-52 years for familial ALS. Some of the characteristics of this disease include:

• Limb-onset ALS- difficulty whilst performing normal motor tasks. Limb onset ALS can be upper motor neuron (UMN) or lower motor neuron (LMN) associated. This trait is present in around 70% of ALS patients
• Bulbar-onset ALS- difficulty associated with specific actions (such as speaking and swallowing) where limb-related motor problems can develop in later stages. This trait is present in around 25% of ALS patients
• Muscular atrophy- loss of muscle mass
• Weight loss- Approximately 50-60% of ALS patients display hypermetabolism (accelerated metabolic activity)
• Respiratory involvement/failure- trait observed in ~5% of ALS patients

Diagnosis

Diagnosis is mainly established by clinical signs assessment focused on:

• UMN- upper motor neuron involvement
• LMN - lower motor neuron involvement

Treatment

• Riluzole- it is suggested that this treatment prolongs survival for up to 3-6 months
• Percutaneous gastrostomy tube- insertion of a feeding tube through the skin. This method is applied in patients with excessive weight loss

5) Add a header called “Summary” at the end of the article discussing the key points and anything else you think needs to be added. 

Summary

Neurodegenerative diseases are characterized by neuronal death, with many leading to loss of quality of life, or increased risk for mortality. The target population is Most neurodegeneration occurs in the ageing population. These types of diseases are mostly of unknown background, although onset can be influenced by both genetic and environmental factors. Some of the most common neurodegenerative diseases are Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis. No cure for neurodegenerative conditions is available to date, but research and advances in medicine are ongoing. Nowadays, more screening methods are being performed, allowing the diagnosis of these illnesses at an early and more manageable stage.