There is no cure or treatment for GSS. It can, however, be identified through genetic testing. GSS is the slowest to progress among human prion diseases. Duration of illness can range from 3 months to 13 years, with an average duration of 5 or 6 years.

GSS is one of a small number of diseases that are caused by prions, a class of pathogenic proteins highly resistant to proteases.

A change in codon 102 from proline to leucine has been found in the prion protein gene ("PRNP", on chromosome 20) of most affected individuals. Therefore, it appears this genetic change is usually required for the development of the disease.

Survival rates for those diagnosed with typical PKAN is 11.18 years with a standard deviation of 7.8 years.

Patients with severe forms of MJD have a life expectancy of approximately 35 years. Those with mild forms have a normal life expectancy. The cause of death of those who die early is often aspiration pneumonia.

Currently, no research has shown a higher prevalence of most leukodsytrophy types in any one place around the world. There is, however, a higher prevalence of the Canavan disease in the Jewish population for unknown reasons. 1 in 40 individuals of Ashkenazi Jewish descent are carriers of Canavan disease. This estimates to roughly 2.5%. Additionally, due to an autosomal recessive inheritance patterns, there is no significant difference found between affected males and affected females for most types of leukodystrophy including, but not limited to, metachromatic leukodystrophy, Krabbe disease, Canavan disease, and Alexander disease. The one exception to this is any type of leukodystrophy carried on a sex chromosome, such as X-linked adrenoleukodystrophy, which is carried on the X-chromosome. Because of the inheritance pattern of X-linked diseases, males are more often affected by this type of leukodystrophy, although female carriers are often symptomatic, though not as severely so as males. To date, there have been no found cases of a leukodystrophy carried on the Y chromosome.

The prognosis is generally poor. With early onset, death usually occurs within 10 years from the onset of symptoms. Individuals with the infantile form usually die before the age of 7. Usually, the later the disease occurs, the slower its course is.

Neurodegeneration is the progressive loss of structure or function of neurons, including death of neurons. Many neurodegenerative diseases – including amyotrophic lateral sclerosis, Parkinson's, Alzheimer's, and Huntington's – occur as a result of neurodegenerative processes. Such diseases are incurable, resulting in progressive degeneration and/or death of neuron cells. As research progresses, many similarities appear that relate these diseases to one another on a sub-cellular level. Discovering these similarities offers hope for therapeutic advances that could ameliorate many diseases simultaneously. There are many parallels between different neurodegenerative disorders including atypical protein assemblies as well as induced cell death. Neurodegeneration can be found in many different levels of neuronal circuitry ranging from molecular to systemic.

Its occurrence is very rare. The infantile form from birth to 2 years of age. The average duration of the infantile form of the illness is usually about 3 years. Onset of the juvenile form presents between two and twelve years of age. Duration of this form is in most cases about 6 years. The adult form from twelve years and older. In younger patients, seizures, megalencephaly, developmental delay, and spasticity are usually present. Neonatal onset is also reported. Onset in adults is least frequent. In older patients, bulbar or pseudobulbar symptoms and spasticity predominate. Symptoms of the adult form may also resemble multiple sclerosis.

There are no more than 500 reported cases.

HDL1 is an unusual, autosomal dominant familial prion disease. Only described in one family, it is caused by an eight-octapeptide repeat insertion in the "PRNP" gene. More broadly, inherited prion diseases in general can mimic HD.

The Huntington's disease-like syndromes (often abbreviated as HD-like or "HDL" syndromes) are a family of inherited neurodegenerative diseases that closely resemble Huntington's disease (HD) in that they typically produce a combination of chorea, cognitive decline or dementia and behavioural or psychiatric problems.

Exercise in middle age may reduce the risk of Parkinson's disease later in life. Caffeine also appears protective with a greater decrease in risk occurring with a larger intake of caffeinated beverages such as coffee. People who smoke cigarettes or use smokeless tobacco are less likely than non-smokers to develop PD, and the more they have used tobacco, the less likely they are to develop PD. It is not known what underlies this effect. Tobacco use may actually protect against PD, or it may be that an unknown factor both increases the risk of PD and causes an aversion to tobacco or makes it easier to quit using tobacco.

Antioxidants, such as vitamins C and E, have been proposed to protect against the disease, but results of studies have been contradictory and no positive effect has been proven. The results regarding fat and fatty acids have been contradictory, with various studies reporting protective effects, risk-increasing effects or no effects. There have been preliminary indications that the use of anti-inflammatory drugs and calcium channel blockers may be protective. A 2010 meta-analysis found that nonsteroidal anti-inflammatory drugs (apart from aspirin), have been associated with at least a 15 percent (higher in long-term and regular users) reduction of incidence of the development of Parkinson's disease.

Early-onset Alzheimer's disease, also called early-onset Alzheimer's, or early-onset AD, is Alzheimer's disease diagnosed before the age of 65. It is an uncommon form of Alzheimer's, accounting for only 5-10% of all Alzheimer's cases. Approximately 13% of the cases of early-onset Alzheimer's are familial Alzheimer's disease, where a genetic predisposition leads to the disease. The other incidences of early onset Alzheimer's, however, share the same traits as the 'late onset' form of Alzheimer's disease, and little is understood about how it starts.

Non-familial early onset Alzheimer's can develop in people who are in their thirties or forties, but that is extremely rare. The majority of people with early-onset Alzheimer's are in their fifties or early sixties.

Familial Alzheimer's disease (FAD) or early onset familial Alzheimer's disease (EOFAD) is an uncommon form of Alzheimer's disease that usually strikes earlier in life, defined as before the age of 65 (usually between 50 and 65 years of age, but can be as early as 15) and is inherited in an autosomal dominant fashion, identified by genetics and other characteristics such as the age of onset. It accounts for approximately half the cases of early-onset Alzheimer's disease. Familial AD requires the patient to have at least one first degree relative with a history of AD. Non-familial cases of AD are referred to as "sporadic" AD, where genetic risk factors are minor or unclear.

While early-onset familial AD is estimated to account for only 3.5% of total Alzheimer's disease, it has presented a useful model in studying various aspects of the disorder. Currently, the early-onset familial AD gene mutations guide the vast majority of animal model based therapeutic discovery and development for AD.

Prevalence data regarding this disorder remains incomplete, however it is estimated that anywhere between 1 in 1,000,000 to 3 in 1,000,000 individuals will be afflicted with this disorder (based upon observed cases in a population), but once again this is only an estimate as the disease is so rare it is difficult to statistically and accurately ascertain.

Pick's disease is a term that can be used in two different ways. It has traditionally been used as a term for a group of neurodegenerative diseases with symptoms attributable to frontal and temporal lobe dysfunction. Common symptoms that are noticed early are personality and emotional changes, as well as deterioration of language. This condition is now more commonly called frontotemporal dementia by professionals, and the use of "Pick's disease" as a clinical diagnosis has fallen out of fashion. The second use of the term (and the one now used among professionals) is to mean a specific pathology that is one of the causes of frontotemporal lobar degeneration. These two uses have previously led to confusion among professionals and patients and so its use should be restricted to the specific pathological subtype described below. It is also known as Pick disease and PiD (not to be confused with pelvic inflammatory disease (PID) or Parkinson's disease (PD)). A defining characteristic of the disease is build-up of tau proteins in neurons, accumulating into silver-staining, spherical aggregations known as "Pick bodies".

Batten disease is a fatal disease of the nervous system that typically begins in childhood. Onset of symptoms is usually between 5 and 10 years of age. Often it is autosomal recessive. It is the most common form of a group of disorders called the neuronal ceroid lipofuscinoses (NCLs).

Although Batten disease is usually regarded as the juvenile form of NCL (or "type 3"), some physicians use the term Batten disease to describe all forms of NCL. Historically, the NCLs were classified by age of disease onset as infantile NCL (INCL), late infantile NCL (LINCL), juvenile NCL (JNCL) or adult NCL (ANCL). At least 20 genes have been identified in association with Batten disease, but juvenile NCL, the most prevalent form of Batten disease, has been linked to mutations in the "CLN3" gene.

It was first described in 1903.

Parkinson-plus syndromes are usually more rapidly progressive and less likely to respond to antiparkinsonian medication than PD. However, the additional features of the diseases may respond to medications not used in PD.

Current therapy for Parkinson-plus syndromes is centered around a multidisciplinary treatment of symptoms.

These disorders have been linked to pesticide exposure.

The prevalence and incidence remain unknown but FTDP-17 is an extremely rare condition. It is caused by mutations in the MAPT gene, which encodes a microtubule-binding protein. Over 100 families with 38 different mutations in the tau gene have been identified worldwide. The phenotype of FTDP-17 varies not only between families carrying different mutations but also between and within families carrying the same mutations.

PD invariably progresses with time. A severity rating method known as the Unified Parkinson's disease rating scale (UPDRS) is the most commonly used metric for clinical study. A modified version known as the MDS-UPDRS is also sometimes used. An older scaling method known as the Hoehn and Yahr scale (originally published in 1967), and a similar scale known as the Modified Hoehn and Yahr scale, have also been commonly used. The Hoehn and Yahr scale defines five basic stages of progression.

Motor symptoms, if not treated, advance aggressively in the early stages of the disease and more slowly later. Untreated, individuals are expected to lose independent ambulation after an average of eight years and be bedridden after ten years. However, it is uncommon to find untreated people nowadays. Medication has improved the prognosis of motor symptoms, while at the same time it is a new source of disability, because of the undesired effects of levodopa after years of use. In people taking levodopa, the progression time of symptoms to a stage of high dependency from caregivers may be over 15 years. However, it is hard to predict what course the disease will take for a given individual. Age is the best predictor of disease progression. The rate of motor decline is greater in those with less impairment at the time of diagnosis, while cognitive impairment is more frequent in those who are over 70 years of age at symptom onset.

Since current therapies improve motor symptoms, disability at present is mainly related to non-motor features of the disease. Nevertheless, the relationship between disease progression and disability is not linear. Disability is initially related to motor symptoms. As the disease advances, disability is more related to motor symptoms that do not respond adequately to medication, such as swallowing/speech difficulties, and gait/balance problems; and also to levodopa-induced complications, which appear in up to 50% of individuals after 5 years of levodopa usage. Finally, after ten years most people with the disease have autonomic disturbances, sleep problems, mood alterations and cognitive decline. All of these symptoms, especially cognitive decline, greatly increase disability.

The life expectancy of people with PD is reduced. Mortality ratios are around twice those of unaffected people. Cognitive decline and dementia, old age at onset, a more advanced disease state and presence of swallowing problems are all mortality risk factors. On the other hand, a disease pattern mainly characterized by tremor as opposed to rigidity predicts an improved survival. Death from aspiration pneumonia is twice as common in individuals with PD as in the healthy population.

In 2013 PD resulted in about 103,000 deaths globally, up from 44,000 deaths in 1990. The death rate increased from an average of 1.5 to 1.8 per 100,000 during that time.

Incidence can vary greatly from type-to-type, and from country-to-country.

In Germany, one study reported an incidence of 1.28 per 100,000.

A study in Italy reported an incidence of 0.56 per 100,000.

A study in Norway reported an incidence of 3.9 per 100,000 using the years from 1978 to 1999, with a lower rate in earlier decades.

Batten disease is a terminal illness; the FDA has approved Brineura (cerliponase alfa) as a treatment for a specific form of Batten disease. Brineura is the first FDA-approved treatment to slow loss of walking ability (ambulation) in symptomatic pediatric patients 3 years of age and older with late infantile neuronal ceroid lipofuscinosis type 2 (CLN2), also known as tripeptidyl peptidase-1 (TPP1) deficiency. Palliative treatment is symptomatic and supportive.

The symptoms of Pick's disease include difficulty in language and thinking, efforts to dissociate from family, behavioral changes, unwarranted anxiety, irrational fears, CBD (Compulsive buying disorder, or oniomania), impaired regulation of social conduct (e.g., breaches of etiquette, vulgar language, tactlessness, , misperception), passivity, low motivation (aboulia), inertia, over-activity, pacing and wandering. It is a characteristic of Pick’s disease that dysfunctional, argumentative, or hostile social conduct is initially exhibited towards family members and not initially exhibited in a workplace or neutral environment. The changes in personality allow doctors to distinguish between Pick's disease and Alzheimer's disease. Pick's disease is one of the causes of the clinical syndrome of frontotemporal lobar degeneration which has three subtypes. Pick's disease pathology is associated more with the frontotemporal dementia and progressive nonfluent aphasia subtypes than the semantic dementia subtype.

The disease is caused by a mutation in the ATXN3 gene, which is located on chromosome 14q. The gene contains lengthy irregular repetitions of the code "CAG", producing a mutated protein called ataxin-3. (Normally, the number of copies is between 13 and 41.) MJD is an autosomal dominant disease, meaning that if either parent gives the defective gene to a child, the child will show symptoms of the disease. Therefore, if one parent suffers from this disease and the other parent does not, there will be a 50% chance of their child inheriting the disease.

The pons (a structure located on the brain stem) is one of the areas affected by MJD. The striatum (a brain area connected to balance and movement) is also affected by this disease, which could explain both of the main motor problems cause by MJD: the tightening and twisting of the limb and the abrupt, irregular movements.

In affected cells, this protein builds up and assembles intranuclear inclusion bodies. These insoluble aggregates are hypothesized to interfere with the normal activity of the nucleus and induce the cell to degenerate and die.

Batten disease is a rare and fatal recessive neurodegenerative disorder that begins at birth.

MSA usually progresses more quickly than Parkinson's disease. There is no remission from the disease. The average remaining lifespan after the onset of symptoms in patients with MSA is 7.9 years. Almost 80% of patients are disabled within five years of onset of the motor symptoms, and only 20% survive past 12 years. Rate of progression differs in every case and speed of decline may vary widely in individual patients.

O’Sullivan and colleagues (2008) identified early autonomic dysfunction to be the most important early clinical prognostic feature regarding survival in MSA. Patients with concomitant motor and autonomic dysfunction within three years of symptom onset had a shorter survival duration, in addition to becoming wheelchair dependent and bed-ridden at an earlier stage than those who developed these symptoms after three years from symptom onset. Their study also showed that when patients with early autonomic dysfunction develop frequent falling, or wheelchair dependence, or severe dysphagia, or require residential care, there is a shorter interval from this point to death.