Brain Diseases and Disorders
This section covers the most common brain disorders and explain at physiological level what is happening to the brain. More than 1,000 disorders of the brain and nervous system result in more hospitalizations and lost productivity than any other disease group, including heart disease and cancer.
What Can Go Wrong?
- Neurodevelopmental disorders occur early in life and are related to disruptions in early organization and development of the nervous system.
- Neurodegenerative disorders involve the progressive degeneration of certain neurons within the brain, and often involve the formation of plaques within diseased cells.
- Psychiatric disorders involve disturbances in mood or behaviour. These include disorders such as anxiety or depression.
- Other problems include tumors or abnormal growths as well as infection.
Note that there are many different terms to describe these disorders, with some overlap. Oftentimes, many of these disorders are comorbid, meaning that someone with one certain brain disorder is also likely to have another (i.e. Depression and Anxiety).
Neurodevelopmental Disorders
Neurodevelopmental disorders are a group of conditions which emerge in early to mid-childhood, characterized by developmental deficits such as impaired social and/or academic skills, lack of self-control and difficulties managing emotions. These disorders are caused by impaired growth of or damage to the central nervous system during early brain development.
Each type of neurodevelopmental disorder has its own characteristic symptoms, which can be treated and sometimes even cured through appropriate behavioral or chemical therapies. Approximately 1% of the population is affected by neurodevelopmental disorders not including the family members who care for them.
| Disorder | Symptoms | Causes | Treatments |
| Autism Spectrum Disorders (ASD) | Deficits in social communication and interaction, restrictive repetitive patterns of behavior, unusual sensory behaviors. | Exact causes are unknown. Genetic predisposition to the disorder combined with premature birth, embryonic exposure to alcohol and certain medications or other environmental triggers are the suspected causes of the disorder. | No medications exist that can cure ASD or treat its core symptoms. Certain medications can improve functions impaired by ASD, while various forms of talk and behavior therapy are used to treat each individual’s specific symptoms. |
| Tourette’s Syndrome (a tic disorder) | Presence of motor and vocal tics, ie. sudden rapid recurrent arrhythmic motor movements or vocalizations. Three to four times more prevalent in males than females. | Exact causes are unknown, but genetic causes with environmental triggers are suspected. Abnormalities in basal ganglia and frontal lobe circuits are suspected to play a role, along with neurotransmitter defects. | There exists no cure. However, medications such as neuroleptics are used to suppress tics, along with behavioral therapy. Both medications and therapy are also used to treat any co-occurring conditions. |
| Down Syndrome (Trisomy 21) | Short stature, abnormal fingerprints, heart defects, poor muscle tone, delayed intellectual development. | An extra chromosome 21. | Treatments are based on each individual’s physical and intellectual needs. These include speech-language, physical, occupational and emotional and behavioral therapies. Assistive technologies such as hearing amplification devices, movement bands and touchscreen computers alleviate stress due to symptoms. |
Neurodegenerative disorders
Neurodegenerative disorders are age-related diseases that degenerate (damage and/or destroy) neurons, resulting in difficulties with movement and/or cognitive impairment. All neurodegenerative diseases exhibit some combination of neuronal cell loss, nervous tissue atrophy, glial cell loss and harmful protein aggregates (build-up of misfolded proteins in cells which disrupt normal cell function). The mechanisms behind that neuronal damage include oxidative stress (imbalance of free radicals which can lead to tissue damage), mitochondrial dysfunction, loss of growth factors (molecules which support neuron development) and neuroinflammation (inflammation of nerve tissue).
The risk of contracting a neurodegenerative disease increases with age (partially due to mitochondrial deterioration and increased likelihood of protein misfolding), and as the elder population continues to grow, neurodegenerative diseases are becoming one of the world’s largest medical burdens.
Neurodegenerative diseases are also difficult to accurately diagnose, as there are no objective imaging or laboratory tests which can confirm diagnoses based on clinical symptomatic criteria. Since currently available therapies only treat the symptoms of neurodegeneration, patients with these disorders progressively get worse, and costs of treatment continue to skyrocket without many beneficial results.
| Disease | Symptoms | Neuropathology | Causes | Treatments |
| Alzheimer’s disease (AD) | significant cognitive decline, memory impairment, difficulty in verbal fluency and naming. | Atrophy in temporal and parietal cortex, amyloid plaques, neurofibrillary tangles (tau protein aggregates). | Hypothesized causes include: Neuronal cell loss, protein misfolding, deposition of excessively phosphorylated tau proteins in neuron cell bodies and processes. Genetics and vascular conditions play a role. | The medications Acetylcholinesterase inhibitors and memantine can somewhat improve cognitive function, but there is no long term cure. |
| Parkinson’s disease (PD) | Resting tremor, bradykinesia (slowness of movement), rigidity, gait imbalance, cognitive impairment, psychiatric symptoms (often depression and anxiety), autonomic dysfunction, sleep disturbances, loss of sense of smell and constipation occur sometimes 10 years prior to other symptoms | Loss of dopaminergic neurons within the substantia nigra with associated Lewy bodies (abnormal protein aggregates). | Genetics, environmental factors (such as exposure to pesticides), buildup of protein aggregates (plaques and tangles). | Most medications boost dopamine neurochemistry, countering the loss of dopaminergic neurons; these include Levadopa, monoamine oxidase inhibitors, and catechol-o-methytransferase. Other therapies include surgical intervention and deep brain stimulation. |
| Amyotrophic Lateral Sclerosis (ALS) Also known as Lou Gehrig’s disease | Weakness and atrophy first develop in one muscle group (eg. in one limb) then spread to other parts of the body until the patient eventually develops respiratory failure. | Loss of lower motor neurons in the anterior horn of the spinal cord and cranial motor nuclei, degeneration and loss of upper motor neurons in the motor cortex (especially Betz cells). | 5-10% of ALS is inheritable, caused by mutations in one of several genes. These genetic factors interact with exposure to toxins and pesticides, smoking, warfare and/or certain viruses to cause ALS.. | The medication Riluzole, a glutamate blocker, extends patient lifespan a few months; no other therapy has slowed or stopped disease progression. |
| Huntington’s disease (HD) | Adult onset HD: psychiatric illness (depression, anxiety, behavioral disturbances), executive cognitive impairment, motor dysfunction (excessive involuntary movements, incoordination, bradykinesia, impaired eye movements). Juvenile HD: akinesia, rigidity, cerebellar ataxia (lack of gait control and coordination), seizures. | Atrophy of the striatum and cortex, significant loss of medium spiny neurons and glial cells in the caudate, huntingtin protein aggregates in neuronal nuclei. | CAG trinucleotide expansion (extra repeats of the nucleotides cytosine-adenine-guanine) in the Huntingtin (htt) gene. | Choreic motor dysfunction (involuntary spasmodic muscle jerking)can be treated with dopamine inhibitors (tetrabenazine, dopamine receptor antagonists). Comorbid psychiatric disorders can be treated with antidepressants or dopamine receptor antagonists (for psychosis). |
Psychiatric disorders
| Disorder | Symptoms | Causes | Treatments |
| Generalised Anxiety Disorder | Hyperactive fear response and worrying that impedes daily functioning | Genetic predisposition; trauma (particularly childhood abuse and neglect); hypothalamic-pituitary-adrenal axis dysregulation | Psychotherapies, such as cognitive behavioural therapy; selective serotonin reuptake inhibitors; benzodiazepines |
| Major Depressive Disorder | Sadness, anhedonia (inability to feel pleasure), and rumination often accompanied by psychosomatic changes in appetite, sleep, and libido | Genetic predisposition; dysregulation of emotional processing network | Psychotherapies, such as cognitive behavioural therapy; selective serotonin reuptake inhibitors; electroconvulsive therapy |
| Bipolar Disorder | Cyclic episodes of depression (resembles Major Depressive Disorder) and mania (characterised by increased energy and may include hallucinations and delusions) | The exact cause is unknown but there are a number of possible factors including genetic predisposition, brain-chemical imbalances, hormonal imbalances, and environmental factors. | Symptoms are typically treated with psychotherapy and a combination of medications that may include mood stabilizers, antipsychotics, and (controversially) antidepressants. |
| Schizophrenia | Anhedonia, disorganised thought, hallucinations, and delusions | Genetic predisposition and prenatal stressors; use of stimulant drugs | First-generation antipsychotics help to relieve hallucinations and delusions; second-generation antipsychotics help to relieve a wider range of symptoms |