Brain MRI shows vermis atrophy or hypoplasic. Cerebral and cerebellar atrophy with white matter changes in some cases.

Diagnosis of MSS is based on clinical symptoms, magnetic resonance imaging (MRI) of the brain (cerebellar atrophy particularly involving the cerebellar vermis), and muscle biopsy.

It can be associated with mutations of the SIL1 gene, and a mutation can be found in about 50% of cases.

Differential diagnosis includes Congenital Cataracts Facial Dysmorphism Neuropathy (CCFDN), Marinesco–Sjögren like syndrome with chylomicronemia, carbohydrate deficient glycoprotein syndromes, Lowe syndrome, and mitochondrial disease.

The diagnosis of A-T is usually suspected by the combination of neurologic clinical features (ataxia, abnormal control of eye movement, and postural instability) with telangiectasia and sometimes increased infections, and confirmed by specific laboratory abnormalities (elevated alpha-fetoprotein levels, increased chromosomal breakage or cell death of white blood cells after exposure to X-rays, absence of ATM protein in white blood cells, or mutations in each of the person’s ATM genes).

A variety of laboratory abnormalities occur in most people with A-T, allowing for a tentative diagnosis to be made in the presence of typical clinical features. Not all abnormalities are seen in all patients. These abnormalities include:

- Elevated and slowly increasing alpha-fetoprotein levels in serum after 2 years of age

- Immunodeficiency with low levels of immunoglobulins (especially IgA, IgG subclasses, and IgE) and low number of lymphocytes in the blood

- Chromosomal instability (broken pieces of chromosomes)

- Increased sensitivity of cells to x-ray exposure (cells die or develop even more breaks and other damage to chromosomes)

- Cerebellar atrophy on MRI scan

The diagnosis can be confirmed in the laboratory by finding an absence or deficiency of the ATM protein in cultured blood cells, an absence or deficiency of ATM function (kinase assay), or mutations in both copies of the cell’s ATM gene. These more specialized tests are not always needed, but are particularly helpful if a child’s symptoms are atypical.

Diagnosis is suspected clinically and family history, neuroimaging and genetic study helps to confirm Behr Syndrome.

Treatment for MSS is symptomatic and supportive including physical and occupational therapy, speech therapy, and special education. Cataracts must be removed when vision is impaired, generally in the first decade of life. Hormone replacement therapy is needed if hypogonadism is present.

Diffuse, symmetric white matter abnormalities were demonstrated by magnetic resonance imaging (MRI) suggesting that Behr syndrome may represent a disorder of white matter associated with an unknown biochemical abnormality.

Only symptomatic treatment for the management of disturbances can be indicated for affected individuals. The genetic origin of this disease would indicate gene therapy holds the most promise for future development of a cure. But at this time no specific treatments for Flynn–Aird syndrome exist.

Gillespie syndrome is a heterogeneous disorder, and can be inherited in either an autosomal dominant or recessive manner. Autosomal dominant inheritance indicates that the defective gene responsible for a disorder is located on an autosome, and only one copy of the gene is sufficient to cause the disorder, when inherited from a parent who has the disorder.

Autosomal recessive inheritance means the defective gene responsible for the disorder is located on an autosome, but two copies of the defective gene (one inherited from each parent) are required in order to be born with the disorder. The parents of an individual with an autosomal recessive disorder both carry one copy of the defective gene, but usually do not experience any signs or symptoms of the disorder.

PAX6 gene analysis can also be helpful to distinguish between autosomal dominant aniridia and Gillespie syndrome. However Atypical Gillespie syndrome is associated mutation with "PAX6 gene".

To illucidate the underlying genetic defects karyotyping and the search for de novo translocations especially of chromosome X and 11 should be performed.

Different types of ataxia:

- congenital ataxias (developmental disorders)

- ataxias with metabolic disorders

- ataxias with a DNA repair defect

- degenerative ataxias

- ataxia associated with other features.

Clinical diagnosis is conducted on individuals with age onset between late teens and late forties who show the initial characteristics for the recessive autosomal cerebellar ataxia.

The following tests are performed:

- MRI brain screening for cerebellum atrophy.

- Molecular genetic testing for SYNE-1 sequence analysis.

- Electrophysiologic studies for polyneurotherapy

- Neurological examination

Prenatal diagnosis and preimplantation genetic diagnosis (PGD) can be performed to identify the mothers carrying the recessive genes for cerebellar ataxia.

Molecular (DNA) testing for PAX6 gene mutations (by sequencing of the entire coding region and deletion/duplication analysis) is available for isolated aniridia and the Gillespie syndrome. For the WAGR syndrome, high-resolution cytogenetic analysis and fluorescence in situ hybridization (FISH) can be utilized to identify deletions within chromosome band 11p13, where both the PAX6 and WT1 genes are located.

Research on the risk for developing schizophrenia in Ashkenazi Jews and other populations showed that 3q29 microdeletion syndrome leads to a significant higher rate of schizophrenia.

Cytogenetic analysis for fragile X syndrome was first available in the late 1970s when diagnosis of the syndrome and carrier status could be determined by culturing cells in a folate deficient medium and then assessing for "fragile sites" (discontinuity of staining in the region of the trinucleotide repeat) on the long arm of the X chromosome. This technique proved unreliable, however, as the fragile site was often seen in less than 40% of an individual's cells. This was not as much of a problem in males, but in female carriers, where the fragile site could generally only be seen in 10% of cells, the mutation often could not be visualised.

Since the 1990s, more sensitive molecular techniques have been used to determine carrier status. The fragile X abnormality is now directly determined by analysis of the number of CGG repeats using polymerase chain reaction (PCR) and methylation status using Southern blot analysis. By determining the number of CGG repeats on the X chromosome, this method allows for more accurate assessment of risk for premutation carriers in terms of their own risk of fragile X associated syndromes, as well as their risk of having affected children. Because this method only tests for expansion of the CGG repeat, individuals with FXS due to missense mutations or deletions involving "FMR1" will not be diagnosed using this test and should therefore undergo sequencing of the FMR1 gene if there is clinical suspicion of FXS.

Prenatal testing with chorionic villus sampling or amniocentesis allows diagnosis of FMR1 mutation while the fetus is in utero and appears to be reliable.

Early diagnosis of fragile X syndrome or carrier status is important for providing early intervention in children or fetuses with the syndrome, and allowing genetic counselling with regards to the potential for a couple's future children to be affected. Most parents notice delays in speech and language skills, difficulties in social and emotional domains as well as sensitivity levels in certain situations with their children.

All individuals with A-T should have at least one comprehensive immunologic evaluation that measures the number and type of lymphocytes in the blood (T-lymphocytes and B-lymphocytes), the levels of serum immunoglobulins (IgG, IgA, and IgM) and antibody responses to T-dependent (e.g., tetanus, Hemophilus influenzae b) and T-independent (23-valent pneumococcal polysaccharide) vaccines. For the most part, the pattern of immunodeficiency seen in an A-T patient early in life (by age five) will be the same pattern seen throughout the lifetime of that individual. Therefore, the tests need not be repeated unless that individual develops more problems with infection. Problems with immunity sometimes can be overcome by immunization. Vaccines against common bacterial respiratory pathogens such as Hemophilus influenzae, pneumococci and influenza virus (the “flu”) are commercially available and often help to boost antibody responses, even in individuals with low immunoglobulin levels. If the vaccines do not work and the patient continues to have problems with infections, gamma globulin therapy (IV or subcutaneous infusions of antibodies collected from normal individuals) may be of benefit. A small number of people with A-T develop an abnormality in which one or more types of immunoglobulin are increased far beyond the normal range. In a few cases, the immunoglobulin levels can be increased so much that the blood becomes thick and does not flow properly. Therapy for this problem must be tailored to the specific abnormality found and its severity.

If an individual patient’s susceptibility to infection increases, it is important to reassess immune function in case deterioration has occurred and a new therapy is indicated. If infections are occurring in the lung, it is also important to investigate the possibility of dysfunctional swallow with aspiration into the lungs (see above sections under Symptoms: Lung Disease and Symptoms: Feeding, Swallowing and Nutrition.)

Most people with A-T have low lymphocyte counts in the blood. This problem seems to be relatively stable with age, but a rare number of people do have progressively decreasing lymphocyte counts as they get older. In the general population, very low lymphocyte counts are associated with an increased risk for infection. Such individuals develop complications from live viral vaccines (measles, mumps, rubella and chickenpox), chronic or severe viral infections, yeast infections of the skin and vagina, and opportunistic infections (such as pneumocystis pneumonia). Although lymphocyte counts are often as low in people with A-T, they seldom have problems with opportunistic infections. (The one exception to that rule is that problems with chronic or recurrent warts are common.) The number and function of T-lymphocytes should be re-evaluated if a person with A-T is treated with corticosteroid drugs such as prednisone for longer than a few weeks or is treated with chemotherapy for cancer. If lymphocyte counts are low in people taking those types of drugs, the use of prophylactic antibiotics is recommended to prevent opportunistic infections.

If the tests show significant abnormalities of the immune system, a specialist in immunodeficiency or infectious diseases will be able to discuss various treatment options. Absence of immunoglobulin or antibody responses to vaccine can be treated with replacement gamma globulin infusions, or can be managed with prophylactic antibiotics and minimized exposure to infection. If antibody function is normal, all routine childhood immunizations including live viral vaccines (measles, mumps, rubella and varicella) should be given. In addition, several “special” vaccines (that is, licensed but not routine for otherwise healthy children and young adults) should be given to decrease the risk that an A-T patient will develop lung infections. The patient and all household members should receive the influenza (flu) vaccine every fall. People with A-T who are less than two years old should receive three (3) doses of a pneumococcal conjugate vaccine (Prevnar) given at two month intervals. People older than two years who have not previously been immunized with Prevnar should receive two (2) doses of Prevnar. At least 6 months after the last Prevnar has been given and after the child is at least two years old, the 23-valent pneumococcal vaccine should be administered. Immunization with the 23-valent pneumococcal vaccine should be repeated approximately every five years after the first dose.

In people with A-T who have low levels of IgA, further testing should be performed to determine whether the IgA level is low or completely absent. If absent, there is a slightly increased risk of a transfusion reaction. “Medical Alert” bracelets are not necessary, but the family and primary physician should be aware that if there is elective surgery requiring red cell transfusion, the cells should be washed to decrease the risk of an allergic reaction.

People with A-T also have an increased risk of developing autoimmune or chronic inflammatory diseases. This risk is probably a secondary effect of their immunodeficiency and not a direct effect of the lack of ATM protein. The most common examples of such disorders in A-T include immune thrombocytopenia (ITP), several forms of arthritis, and vitiligo.

In at least some case, the gene lesion involves a mutation in the "CSB" gene.

It can be associated with "ERCC6".

EAST syndrome is an autosomal recessive disorder; therefore, it cannot necessarily be prevented. Presence of the four symptoms (epilepsy, ataxia, sensorineural deafness, and salt-wasting renal tubulopathy) and detection of a mutation in the KCNJ10 gene would indicate the presence of this disorder.

There is not yet one method to help EAST syndrome as a whole, but hopefully with continued research, there could be one day.

P. Flynn and Robert B. Aird observed this neuroectodermal syndrome after studying one family whose members suffered a number of neurological symptoms that were consistent from generation to generation. A number of the symptoms overlapped with several known neurological diseases such as Werner syndrome, Refsum syndrome, and Cockayne syndrome, which could be indicative of similar causative origins. However, these syndromes are recessively inherited as opposed to the dominant inheritance seen in the family studied by P. Flynn and Robert B. Aird. About 15% of family members exhibited full-blown symptoms characteristic of the disease while others showed some symptoms that overlapped with the general clinical manifestation of the syndrome.

3q29 microdeletion syndrome is a rare genetic disorder resulting from the deletion of a segment of chromosome 3. This syndrome was first described in 2005.

DeSanctis–Cacchione syndrome is an extremely rare disorder characterized by the skin and eye symptoms of xeroderma pigmentosum (XP) occurring in association with microcephaly, progressive mental retardation, retarded growth and sexual development, deafness, choreoathetosis, ataxia and quadriparesis.

There are no current treatments or cures for the underlying defects of FXS. Management of FXS may include speech therapy, behavioral therapy, sensory integration occupational therapy, special education, or individualised educational plans, and, when necessary, treatment of physical abnormalities. Persons with fragile X syndrome in their family histories are advised to seek genetic counseling to assess the likelihood of having children who are affected, and how severe any impairments may be in affected descendants.

The cause of Primrose syndrome is currently unknown. This condition is extremely rare and seems to spontaneously occur, regardless of family history.

In the case studied by Dalai et al. in 2010, it was found that an abnormally high amount of calcitonin, a hormone secreted by the thyroid gland to stabilize blood calcium levels, was present in the blood serum. This suggests that the thyroid gland is releasing an abnormal amount of calcitonin, resulting in the disruption of calcium level homeostasis. No molecular cause was found, but an expanded microarray analysis of the patient found a 225.5 kb deletion on chromosome 11p between rs12275693 and rs1442927. Whether or not this deletion is related to the syndrome or is a harmless mutation is unknown. The deletion was not present in the patient's mother's DNA sample, but the father's DNA was unavailable.

The common symptoms in all reported cases of primrose syndrome include ossified pinnae, learning disabilities or mental retardation, hearing problems, movement disorders (ataxia, paralysis, and parkinsonism among others (likely due, in part, to calcification of the basal ganglia), a torus palatinus (a neoplasm on the mouth's hard palate), muscle atrophy, and distorted facial features. Other symptoms usually occur, different in each case, but it is unknown whether or not these symptoms are caused by the same disease.

Aniridia may be broadly divided into hereditary and sporadic forms. Hereditary aniridia is usually transmitted in an autosomal dominant manner (each offspring has a 50% chance of being affected), although rare autosomal recessive forms (such as Gillespie syndrome) have also been reported. Sporadic aniridia mutations may affect the WT1 region adjacent to the AN2 aniridia region, causing a kidney cancer called nephroblastoma (Wilms tumor). These patients often also have genitourinary abnormalities and intellectual disability (WAGR syndrome).

Several different mutations may affect the PAX6 gene. Some mutations appear to inhibit gene function more than others, with subsequent variability in the severity of the disease. Thus, some aniridic individuals are only missing a relatively small amount of iris, do not have foveal hypoplasia, and retain relatively normal vision. Presumably, the genetic defect in these individuals causes less "heterozygous insufficiency," meaning they retain enough gene function to yield a milder phenotype.

- AN

- Aniridia and absent patella

- Aniridia, microcornea, and spontaneously reabsorbed cataract

- Aniridia, cerebellar ataxia, and mental deficiency (Gillespie syndrome)

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.

Three main approaches have been used to prevent or reduce the incidence of Tay–Sachs:

- Prenatal diagnosis. If both parents are identified as carriers, prenatal genetic testing can determine whether the fetus has inherited a defective gene copy from both parents. Chorionic villus sampling (CVS), the most common form of prenatal diagnosis, can be performed between 10 and 14 weeks of gestation. Amniocentesis is usually performed at 15–18 weeks. These procedures have risks of miscarriage of 1% or less.

- Preimplantation genetic diagnosis. By retrieving the mother's eggs for in vitro fertilization, it is possible to test the embryo for the disorder prior to implantation. Healthy embryos are then selected and transferred into the mother's womb, while unhealthy embryos are discarded. In addition to Tay–Sachs disease, preimplantation genetic diagnosis has been used to prevent cystic fibrosis and sickle cell anemia among other genetic disorders.

- Mate selection. In Orthodox Jewish circles, the organization Dor Yeshorim carries out an anonymous screening program so that carrier couples for Tay–Sachs and other genetic disorders can avoid marriage.