In terms of frequency, is estimated at 2 per 100,000, it has identified in different regions of the world. Some clusters of certain types of autosomal dominant cerebellar ataxia reach a prevalence of 5 per 100,000.

In most cases, between the age of 2 and 4 oculomotor signals are present. Between the age of 2 and 8, telangiectasias appears. Usually by the age of 10 the child needs a wheel chair. Individuals with autosomal recessive cerebellum ataxia usually survive till their 20s; in some cases individuals have survived till their 40s or 50s.

There is no known prevention of spinocerebellar ataxia. Those who are believed to be at risk can have genetic sequencing of known SCA loci performed to confirm inheritance of the disorder.

The prevalence of SCA6 varies by culture. In Germany, SCA6 accounts for 10-25% of all autosomal dominant cases of SCA (SCA itself having a prevalence of 1 in 100,000). This prevalence in lower in Japan, however, where SCA6 accounts for only ~6% of spinocerebellar ataxias. In Australia, SCA6 accounts for 30% of spinocerebellar ataxia cases while 11% in the Dutch.

Most patients begin to use a wheelchair for movement around age 30-40. Death usually occurs in their 60s, but some have been reported to live longer.

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.

There is no known prevention of spinocerebellar ataxia. Those who are believed to be at risk can have genetic sequencing of known SCA loci performed to confirm inheritance of the disorder.

Behr syndrome is characterized by the association of early-onset optic atrophy with spinocerebellar degeneration resulting in ataxia, pyramidal signs, peripheral neuropathy and developmental delay.

Although it is an autosomal recessive disorder, heterozygotes may still manifest much attenuated symptoms. Autosomal dominant inheritance also being reported in a family. Recently a variant of OPA1 mutation with phenotypic presentation like Behr syndrome is also described. Some reported cases have been found to carry mutations in the OPA1, OPA3 or C12ORF65 genes which are known causes of pure optic atrophy or optic atrophy complicated by movement disorder.

The inheritance pattern is autosomal recessive. The disorder is caused by a mutation in the SGCG on chromosome 13. The mutation of the SACS gene causes the production of an unstable, poorly functioning SACSIN protein. It is unclear as to how this mutation affects the central nervous system (CNS) and skeletal muscles presenting in the signs and symptoms of ARSACS.

Friedreich's ataxia is the most prevalent inherited ataxia, affecting about 1 in 50,000 people in the United States. Males and females are affected equally. The estimated carrier prevalence is 1:110.

A 1984 Canadian study was able to trace 40 cases of classical Friedreich's disease from 14 French-Canadian kindreds previously thought to be unrelated to one common ancestral couple arriving in New France in 1634: Jean Guyon and Mathurine Robin.

40 cases were diagnosed in northern Italy between 1940 and 1990. The gene frequency for this autosomal recessive condition was estimated at 1 in 218. In 1989, 16 cases on EOCA were diagnosed in children with a mean onset age of 7.1 In 1990, 20 patients affected by EOCA were studied. It was found that the ataxia of this study's participants affected the pyramidal tracts and peripheral nerves.

In terms of the genetics of autosomal dominant cerebellar ataxia 11 of 18 known genes are caused by repeated expansions in corresponding proteins, sharing the same mutational mechanism. SCAs can be caused by conventional mutations or large rearrangements in genes that make glutamate and calcium signaling, channel function, tau regulation and mitochondrial activity or RNA alteration.

The mechanism of Type I is not completely known, however Whaley, et al. suggest the polyglutamine product is toxic to the cell at a protein level, this effect may be done by transcriptional dysregulation and disruption of calcium homeostasis which causes apoptosis to occur earlier.

NPCA is a syndrome and can have diverse causes. It has a genetic basis and inheritance is considered to be autosomal recessive. However, autosomal dominant variety has also been reported. There may be familial balanced translocation t(8;20)(p22;q13) involved.

Onset : Early childhood

Progression: Chronic progressive

Clinical: Cerebellar ataxia plus syndrome / Optic Atrophy Plus Syndrome

Ocular: Optic atrophy, nystagmus, scotoma, and bilateral retrobulbar neuritis.

Other: Mental retardation, myoclonic epilepsy, spasticity, and posterior column sensory loss. Tremor in some cases.

Musculoskeletal

Contractures, lower limbs, Achilles tendon contractures, Hamstring contractures, Adductor longus contractures

Systemic

Hypogonadotrophic hypogonadism.

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.

The hereditary ataxias are categorized by mode of inheritance and causative gene or chromosomal locus. The hereditary ataxias can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner.

- Many types of autosomal dominant cerebellar ataxias for which specific genetic information is available are now known. Synonyms for autosomal-dominant cerebellar ataxias (ADCA) used prior to the current understanding of the molecular genetics were Marie's ataxia, inherited olivopontocerebellar atrophy, cerebello-olivary atrophy, or the more generic term "spinocerebellar degeneration." (Spinocerebellar degeneration is a rare inherited neurological disorder of the central nervous system characterized by the slow degeneration of certain areas of the brain. There are three forms of spinocerebellar degeneration: Types 1, 2, 3. Symptoms begin during adulthood.)

- There are five typical "autosomal-recessive" disorders in which ataxia is a prominent feature: Friedreich ataxia, ataxia-telangiectasia, ataxia with vitamin E deficiency, ataxia with oculomotor apraxia (AOA), spastic ataxia. Disorder subdivisions: Friedreich's ataxia, Spinocerebellar ataxia, Ataxia telangiectasia, Vasomotor ataxia, Vestibulocerebellar, Ataxiadynamia, Ataxiophemia, Olivopontocerebellar atrophy, and Charcot-Marie-Tooth disease.

- There have been reported cases where a polyglutamine expansion may lengthen when passed down, which often can result in an earlier age-of-onset and a more severe disease phenotype for individuals who inherit the disease allele. This falls under the category of genetic anticipation.

Ataxia with telangiectasia is a rare form ataxia that causes chromosomal instability, sensitivity to ionizing radiation, disrupted stress-activated signal transduction pathways and radioresistant DNA synthesis.

The genes that underlie majority of the symptoms for the different types of ataxia are still unknown. A productive cure is still unavailable to prevent the brain degeneration associated with ataxia.

Oculomotor ataxia accompanies gait ataxia which causes dysarthria, muscle weakness, loss of joint position sense and limb dysmetria. In some cases, patients have shown mental retardation and loss of myelinated axons.

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.

People with A-T have a highly increased incidence (approximately 25% lifetime risk) of cancers, particularly lymphomas and leukemia, but other cancers can occur. When possible, treatment should avoid the use of radiation therapy and chemotherapy drugs that work in a way that is similar to radiation therapy (radiomimetic drugs), as these are particularly toxic for people with A-T. The special problems of managing cancer are sufficiently complicated that treatment should be done only in academic oncology centers and after consultation with physicians who have specific expertise in A-T. Unfortunately, there is no way to predict which individuals will develop cancer. Because leukemia and lymphomas differ from solid tumors in not progressing from solitary to metastatic stages, there is less need to diagnose them early in their appearance. Surveillance for leukemia and lymphoma is thus not helpful, other than considering cancer as a diagnostic possibility whenever possible symptoms of cancer (e.g. persistent swollen lymph glands, unexplained fever) arise.

Women who are A-T carriers (who have one mutated copy of the ATM gene), have approximately a two-fold increased risk for the development of breast cancer compared to the general population. This includes all mothers of A-T children and some female relatives. Current consensus is that special screening tests are not helpful, but all women should have routine cancer surveillance.

Spinocerebellar ataxia type 13 (SCA13) is a rare autosomal dominant disorder, which, like other types of SCA, is characterized by dysarthria, nystagmus, and ataxia of gait, stance and the limbs due to cerebellar dysfunction. Patients with SCA13 also tend to present with epilepsy, an inability to run, and increased reflexes. This cerebellar dysfunction is permanent and progressive. SCA13 is caused by mutations in KCNC3, a gene encoding a voltage-gated potassium channel K3.3. There are two known mutations in this gene causative for SCA13. Unlike many other types of SCA, these are not polyglutamine expansions but, rather, point mutations resulting in channels with no current or altered kinetics.

The life expectancy of people with A-T is highly variable. The average is approximately 25 years, but continues to improve with advances in care. The two most common causes of death are chronic lung disease (about one-third of cases) and cancer (about one-third of cases).

Harding ataxia, also known as Early onset cerebellar ataxia with retained reflexes (EOCARR), is an autosomal recessive cerebellar ataxia originally described by Harding in 1981. This form of cerebellar ataxia is similar to Friedreich ataxia including that it results in poor reflexes and balance, but differs in several ways, including the absence of diabetes mellitus, optic atrophy, cardiomyopathy, skeletal abnormalities, and the fact that tendon reflexes in the arms and knees remain intact. This form of ataxia is characterized by onset in the first 20 years, and is less severe than Friedreich ataxia. Additional cases were diagnosed in 1989, 1990, 1991, and 1998.

A few SCAs remain unspecified and can not be precisely diagnosed, but in the last decade genetic testing has allowed precise identification of dozens of different SCAs and more tests are being added each year. In 2008, a genetic ataxia blood test developed to test for 12 types of SCA, Friedreich's ataxia, and several others. However, since not every SCA has been genetically identified some SCAs are still diagnosed by neurological examination, which may include a physical exam, family history, MRI scanning of the brain and spine, and spinal tap.

Many SCAs below fall under the category of polyglutamine diseases, which are caused when a disease-associated protein (i.e., ataxin-1, ataxin-3, etc.) contains a large number of repeats of glutamine residues, termed a polyQ sequence or a "CAG trinucleotide repeat" disease for either the one-letter designation or codon for glutamine respectively. The threshold for symptoms in most forms of SCA is around 35, though for SCA3 it extends beyond 50. Most polyglutamine diseases are dominant due to the interactions of resulting polyQ tail.

The first ataxia gene was identified in 1993 and called "Spinocerebellar ataxia type 1" (SCA1); later genes were called SCA2, SCA3, etc. Usually, the "type" number of "SCA" refers to the order in which the gene was found. At this time, there are at least 29 different gene mutations that have been found.

The following is a list of some of the many types of "Spinocerebellar ataxia".

Others include SCA18, SCA20, SCA21, SCA23, SCA26, SCA28, and SCA29.

Four X-linked types have been described (, , , ), but only the first of these has so far been tied to a gene (SCAX1).

The progression of symptoms varies widely between each case of FXTAS; the onset of symptoms may be gradual, with progression of the disease spanning multiple years or decades. Alternatively, symptoms may progress rapidly.

FXTAS has shown strong age-dependent penetrance, afflicting older permutation carriers with greater prevalence. Male carriers, age 50 and above have a 30% chance of acquiring FXTAS, while male carriers, age 75 and above, have a 75% chance of developing FXTAS. While initially described to affect male carriers, female carriers of the FMR1 gene mutation have also been found to develop FXTAS. However, due to X-inactivation, female carriers are much less likely to develop classic ataxia and tremor signs for FXTAS, instead demonstrating symptoms such as fibromyalgia, thyroid disease, hypertension, and seizures.

Non-progressive congenital ataxia (NPCA) is a non-progressive form of cerebellar ataxia which can occur with or without cerebellar hypoplasia.