MJD can be diagnosed by recognizing the symptoms of the disease and by taking a family history. Physicians ask patients questions about the kind of symptoms relatives with the disease had, the progression and harshness of symptoms, and the ages of onset in family members.

Presymptomatic diagnosis of MJD can be made with a genetic test. The direct detection of the genetic mutation responsible for MJD has been available since 1995. Genetic testing looks at the number of CAG repeats within the coding region of the MJD/ATXN3 gene on chromosome 14. The test will show positive for MJD if this region contains 61-87 repeats, as opposed to the 12-44 repeats found in healthy individuals. A limitation to this test is that if the number of CAG repeats in an individual being tested falls between the healthy and pathogenic ranges (45-60 repeats), then the test cannot predict whether an individual will have MJD symptoms.

Computed tomography (CT) scans of people with PD usually appear normal. MRI has become more accurate in diagnosis of the disease over time, specifically through iron-sensitive T2* and SWI sequences at a magnetic field strength of at least 3T, both of which can demonstrate absence of the characteristic 'swallow tail' imaging pattern in the dorsolateral substantia nigra. In a meta-analysis, absence of this pattern was 98% sensitive and 95% specific for the disease. Diffusion MRI has shown potential in distinguishing between PD and Parkinson plus syndromes, though its diagnostic value is still under investigation. CT and MRI are also used to rule out other diseases that can be secondary causes of parkinsonism, most commonly encephalitis and chronic ischemic insults, as well as less frequent entities such as basal ganglia tumors and hydrocephalus.

Dopamine-related activity in the basal ganglia can be directly measured with PET and SPECT scans. A finding of reduced dopamine-related activity in the basal ganglia can rule out drug-induced parkinsonism, but reduced basal ganglia dopamine-related activity is seen in both PD and the Parkinson-plus disorders so these scans are not reliable in distinguishing PD from other neurodegenerative causes of parkinsonism.

To gain a better understanding of the disease, researchers have retrospectively reviewed medical records of probands and others who were assessed through clinical examinations or questionnaires. Blood samples are collected from the families of the probands for genetic testing. These family members are assessed using their standard medical history, on their progression of Parkinson's like symptoms (Unified Parkinson's Disease Rating Scale), and on their progression of cognitive impairment such as dementia (Folstein Test).

Standard MRI scans have been performed on 1.5 Tesla scanners with 5 mm thickness and 5 mm spacing to screen for white matter lesions in identified families. If signal intensities of the MRI scans are higher in white matter regions than in grey matter regions, the patient is considered to be at risk for HDLS, although a number of other disorders can also produce white matter changes and the findings are not diagnostic without genetic testing or pathologic confirmation.

There are five sub-types of MJD that are characterized by the age of onset and range of symptoms.

The sub-types illustrate a wide variety of symptoms that patients can experience. However, assigning individuals to a specific sub-type of the disease is of limited clinical significance.

- Type I is distinguished by arrival between the ages of 10 and 30 and represents approximately 13% of individuals. It usually has fast development and severe rigidity and dystonia.

- Type II is the most common sub-type (approximately 57% of individuals with MJD ) and typically begins between 20 and 50 years of age . It has an intermediate progression and causes symptoms that include spasticity, exaggerated reflex responses and spastic gait, ataxia and upper motor neuron signs.

- Type III MJD has a slow progression. Patients typically have an onset between the ages of 40 and 70 and represent approximately 30% of MJD patients. Symptoms include muscle twitching, tingling, cramps, unpleasant sensations such as numbness, pain in the feet, hands and limbs and muscle atrophy. Nearly all patients experience a decline in their vision such as blurred vision, double vision, inability to control eye movements, and loss of capability to distinguish color. Some patients also experience Parkinsonian symptoms.

- Type IV is distinguished by Parkinsonian symptoms that respond particularly well to levodopa treatment.

- Type V appears to resemble Hereditary Spastic Paraplegia; however, more research is needed to conclude the relationship between Type V MJD and hereditary spastic paraplegia.

Diagnosis of MSA can be challenging because there is no test that can definitively make or confirm the diagnosis in a living patient. Clinical diagnostic criteria were defined in 1998 and updated in 2007. Certain signs and symptoms of MSA also occur with other disorders, such as Parkinson's disease, making the diagnosis more difficult.

Both MRI and CT scanning frequently show a decrease in the size of the cerebellum and pons in those with cerebellar features. The putamen is hypodense on T2-weighted MRI and may show an increased deposition of iron in Parkinsonian form. In cerebellar form, a "hot cross" sign has been emphasized; it reflects atrophy of the pontocereballar fibers that manifest in T2 signal intensity in atrophic pons.

A definitive diagnosis can only be made pathologically on finding abundant glial cytoplasmic inclusions in the central nervous system.

A physician will initially assess for Parkinson's disease with a careful medical history and neurological examination. People may be given levodopa, with any resulting improvement in motor impairment helping to confirm the PD diagnosis. The finding of Lewy bodies in the midbrain on autopsy is usually considered final proof that the person had PD. The clinical course of the illness over time may reveal it is not Parkinson's disease, requiring that the clinical presentation be periodically reviewed to confirm accuracy of the diagnosis.

Other causes that can secondarily produce parkinsonism are stroke and drugs. Parkinson plus syndromes such as progressive supranuclear palsy and multiple system atrophy must be ruled out. Anti-Parkinson's medications are typically less effective at controlling symptoms in Parkinson plus syndromes. Faster progression rates, early cognitive dysfunction or postural instability, minimal tremor or symmetry at onset may indicate a Parkinson plus disease rather than PD itself. Genetic forms with an autosomal dominant or recessive pattern of inheritance are sometimes referred to as familial Parkinson's disease or familial parkinsonism.

Medical organizations have created diagnostic criteria to ease and standardize the diagnostic process, especially in the early stages of the disease. The most widely known criteria come from the UK Queen Square Brain Bank for Neurological Disorders and the U.S. National Institute of Neurological Disorders and Stroke. The Queen Square Brain Bank criteria require slowness of movement (bradykinesia) plus either rigidity, resting tremor, or postural instability. Other possible causes of these symptoms need to be ruled out. Finally, three or more of the following supportive features are required during onset or evolution: unilateral onset, tremor at rest, progression in time, asymmetry of motor symptoms, response to levodopa for at least five years, clinical course of at least ten years and appearance of dyskinesias induced by the intake of excessive levodopa.

When PD diagnoses are checked by autopsy, movement disorders experts are found on average to be 79.6% accurate at initial assessment and 83.9% accurate after they have refined their diagnosis at a follow-up examination. When clinical diagnoses performed mainly by nonexperts are checked by autopsy, average accuracy is 73.8%. Overall, 80.6% of PD diagnoses are accurate, and 82.7% of diagnoses using the Brain Bank criteria are accurate.

A task force of the International Parkinson and Movement Disorder Society (MDS) has proposed diagnostic criteria for Parkinson’s disease as well as research criteria for the diagnosis of prodromal disease, but these will require validation against the more established criteria.

Genetic testing can confirm a neuroferritinopathy diagnosis. A diagnosis can be made by analyzing the protein sequences of affected individuals and comparing them to known neuroferritinopathy sequences.

Blood tests usually come back normal in affected individuals, so they do not serve as a reliable means of diagnosis. Blood tests can show low serum ferritin levels. However, this is unreliable as method of diagnosis, as some patients show typical serum ferritin levels even at the latest stages of neuroferritinopathy. Cerebral spinal fluid tests also are typically normal.

Ferritin found in the skin, liver, kidney, and muscle tissues may help in diagnosing neuroferritinopathy. More cytochrome c oxidase-negative fibers are also often found in the muscle biopsies of affected individuals.

In diagnosing autosomal dominant cerebellar ataxia the individuals clinical history or their past health examinations, a current physical examination to check for any physical abnormalities, and a genetic screening of the patients genes and the genealogy of the family are done. The large category of cerebellar ataxia is caused by a deterioration of neurons in the cerebellum, therefore magnetic resonance imaging (MRI) is used to detect any structural abnormality such as lesions which are the primary cause of the ataxia. Computed tomography (CT) scans can also be used to view neuronal deterioration, but the MRI provides a more accurate and detailed picture.

There is no cure for spinocerebellar ataxia, which is currently considered to be a progressive and irreversible disease, although not all types cause equally severe disability.

In general, treatments are directed towards alleviating symptoms, not the disease itself. Many patients with hereditary or idiopathic forms of ataxia have other symptoms in addition to ataxia. Medications or other therapies might be appropriate for some of these symptoms, which could include tremor, stiffness, depression, spasticity, and sleep disorders, among others. Both onset of initial symptoms and duration of disease are variable. If the disease is caused by a polyglutamine trinucleotide repeat CAG expansion, a longer expansion may lead to an earlier onset and a more radical progression of clinical symptoms. Typically, a person afflicted with this disease will eventually be unable to perform daily tasks (ADLs). However, rehabilitation therapists can help patients to maximize their ability of self-care and delay deterioration to certain extent. Researchers are exploring multiple avenues for a cure including RNAi and the use of Stem Cells and several other avenues.

On January 18, 2017 BioBlast Pharma announced completion of Phase 2a clinical trials of their medication, Trehalose, in the treatment of SCA3. BioBlast has received FDA Fast Track status and Orphan Drug status for their treatment. The information provided by BioBlast in their research indicates that they hope this treatment may prove efficacious in other SCA treatments that have similar pathology related to PolyA and PolyQ diseases.

In addition, Dr. Beverly Davidson has been working on a methodology using RNAi technology to find a potential cure for over 2 decades. Her research began in the mid-1990s and progressed to work with mouse models about a decade later and most recently has moved to a study with non-human primates. The results from her most recent research "are supportive of clinical application of this gene therapy". Dr. Davidson along with Dr. Pedro Gonzalez-Alegre are currently working to move this technique into a Phase 1 clinical trial.

Finally, another gene transfer technology discovered in 2011 has also been shown by Dr. Davidson to hold great promise and offers yet another avenue to a potential future cure.

The degeneration of white matter, which shows the degeneration of myelin, can be seen in a basic MRI and used to diagnose leukodystrophies of all types. T-1 and T-2 weighted FLAIR images are the most useful. FLAIR stands for fluid-attenuated inversion recovery. Electrophysiological and other kinds of laboratory testing can also be done. In particular, nerve conduction velocity is looked at to distinguish between leukodystrophy and other demyelinating diseases, as well as to distinguish between individual leukodystrophies. For example, individuals with X-ALD have normal conduction velocities, while those with Krabbe disease or metachromatic leukodystrophy have abnormalities in their conduction velocities. Next generation multigene sequencing panels for undifferentiated leukodystrophy can now be offered for rapid molecular diagnosis after appropriate genetic counselling.

Due to the condition's rarity, it is frequently misdiagnosed, often as cerebral palsy. This results in patients often living their entire childhood with the condition untreated.

The diagnosis of SS can be made from a typical history, a trial of dopamine medications, and genetic testing. Not all patients show mutations in the GCH1 gene (GTP cyclohydrolase I), which makes genetic testing imperfect.

Sometimes a lumbar puncture is performed to measure concentrations of biopterin and neopterin, which can help determine the exact form of dopamine-responsive movement disorder: early onset parkinsonism (reduced biopterin and normal neopterin), GTP cyclohydrolase I deficiency (both decreased) and tyrosine hydroxylase deficiency (both normal).

In approximately half of cases, a phenylalanine loading test can be used to show decreased conversion from the amino acid phenylalanine to tyrosine. This process uses BH4 as a cofactor.

During a sleep study (polysomnography), decreased twitching may be noticed during REM sleep.

An MRI scan of the brain can be used to look for conditions that can mimic SS (for example, metal deposition in the basal ganglia can indicate Wilson's disease or pantothenate kinase-associated neurodegeneration). Nuclear imaging of the brain using positron emission tomography (PET scan) shows a normal radiolabelled dopamine uptake in SS, contrary to the decreased uptake in Parkinson's disease.

Other differential diagnoses include metabolic disorders (such as GM2 gangliosidosis, phenylketonuria, hypothyroidism, Leigh disease) primarily dystonic juvenile parkinsonism, autosomal recessive early onset parkinsonism with diurnal fluctuation, early onset idiopathic parkinsonism, focal dystonias, dystonia musculorum deformans and dyspeptic dystonia with hiatal hernia.

- Diagnosis - main

- typically referral by GP to specialist Neurological Hospital e.g. National Hospital in London.

- very hard to diagnose as condition is dynamic w.r.t. time-of-day AND dynamic w.r.t. age of patient.

- correct diagnosis only made by a consultant neurologist with a complete 24-hour day-cycle observation(with video/film) at a Hospital i.e. morning(day1)->noon->afternoon->evening->late-night->sleep->morning(day2).

- patient with suspected SS required to walk in around hospital in front of Neuro'-consultant at selected daytime intervals to observe worsening walking pattern coincident with increased muscle tension in limbs.

- throughout the day, reducing leg-gait, thus shoe heels catching one another.

- diurnal affect of condition: morning(fresh/energetic), lunch(stiff limbs), afternoon(very stiff limbs), evening(limbs worsening), bedtime(limbs near frozen).

- muscle tension in thighs/arms: morning(normal), lunch(abnormal), afternoon(very abnormal), evening(bad), bedtime(frozen solid).

- Diagnosis - additional

- lack of self-esteem at school/college/University -> eating disorders in youth thus weight gains.

- lack of energy during late-daytime (teens/adult) -> compensate by over-eating.

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.

Physical therapists can assist patients in maintaining their level of independence through therapeutic exercise programmes. One recent research report demonstrated a gain of 2 SARA points (Scale for the Assessment and Rating of Ataxia) from physical therapy. In general, physical therapy emphasises postural balance and gait training for ataxia patients. General conditioning such as range-of-motion exercises and muscle strengthening would also be included in therapeutic exercise programmes. Research showed that spinocerebellar ataxia 2 (SCA2) patients with a mild stage of the disease gained significant improvement in static balance and neurological indices after six months of a physical therapy exercise training program. Occupational therapists may assist patients with incoordination or ataxia issues through the use of adaptive devices. Such devices may include a cane, crutches, walker, or wheelchair for those with impaired gait. Other devices are available to assist with writing, feeding, and self care if hand and arm coordination are impaired. A randomised clinical trial revealed that an intensive rehabilitation program with physical and occupational therapies for patients with degenerative cerebellar diseases can significantly improve functional gains in ataxia, gait, and activities of daily living. Some level of improvement was shown to be maintained 24 weeks post-treatment. Speech language pathologists may use both behavioral intervention strategies as well as augmentative and alternative communication devices to help patients with impaired speech.

In terms of a cure there is currently none available, however for the disease to manifest itself, it requires mutant gene expression. Manipulating the use of protein homoestasis regulators can be therapuetic agents, or a treatment to try and correct an altered function that makes up the pathology is one current idea put forth by Bushart, et al. There is some evidence that for SCA1 and two other polyQ disorders that the pathology can be reversed after the disease is underway. There is no effective treatments that could alter the progression of this disease, therefore care is given, like occupational and physical therapy for gait dysfunction and speech therapy.

Due to the wide range of genetic disorders that are presently known, diagnosis of a genetic disorder is widely varied and dependent of the disorder. Most genetic disorders are diagnosed at birth or during early childhood, however some, such as Huntington's disease, can escape detection until the patient is well into adulthood.

The basic aspects of a genetic disorder rests on the inheritance of genetic material. With an in depth family history, it is possible to anticipate possible disorders in children which direct medical professionals to specific tests depending on the disorder and allow parents the chance to prepare for potential lifestyle changes, anticipate the possibility of stillbirth, or contemplate termination. Prenatal diagnosis can detect the presence of characteristic abnormalities in fetal development through ultrasound, or detect the presence of characteristic substances via invasive procedures which involve inserting probes or needles into the uterus such as in amniocentesis.

Prognosis strongly depends on which subtype of disease it is. Some are deadly in infancy but most are late onset and mostly manageable.

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.

Not all genetic disorders directly result in death, however there are no known cures for genetic disorders. Many genetic disorders affect stages of development such as Down syndrome. While others result in purely physical symptoms such as muscular dystrophy. Other disorders, such as Huntington's disease show no signs until adulthood. During the active time of a genetic disorder, patients mostly rely on maintaining or slowing the degradation of quality of life and maintain patient autonomy. This includes physical therapy, pain management, and may include a selection of alternative medicine programs.

Though it is only definitively diagnosed by a genetic test, autosomal dominant porencephaly type I can be suspected if the disease is known to run in the family or if someone shows symptoms. CT scanning or MRI may be useful in indicating a diagnosis. COL4A1 may be mutated in other diseases that need to be distinguished, including brain small vessel disease with hemorrhage and HANAC syndrome. CADASIL syndrome is caused by a mutation in a different gene, but may cause similar symptoms. Sporadic porencephaly is another disorder that can appear similar.

The most useful information for accurate diagnosis is the symptoms and weakness pattern. If the quadriceps are spared but the hamstrings and iliopsoas are severely affected in a person between ages of 20 - 40, it is very likely HIBM will be at the top of the differential diagnosis. The doctor may order any or all of the following tests to ascertain if a person has IBM2:

- Blood test for serum Creatine Kinase (CK or CPK);

- Nerve Conduction Study (NCS) / Electomyography (EMG);

- Muscle Biopsy;

- Magnetic Resonance Imaging (MRI) or Computer Tomography (CT) Scan to determine true sparing of quadriceps;

- Blood Test or Buccal swab for genetic testing;

While the clinical picture may point towards the diagnosis of the Roussy–Lévy syndrome, the condition can only be confirmed with absolute certainty by carrying out genetic testing in order to identify the underlying mutations.

Amniocentesis or chorionic villus sampling can be used to screen for the disease before birth. After birth, urine tests, along with blood tests and skin biopsies can be used to diagnose Schindler disease. Genetic testing is also always an option, since different forms of Schindler disease have been mapped to the same gene on chromosome 22; though different changes (mutations) of this gene are responsible for the infantile- and adult-onset forms of the disease.

This condition is very rare, only affecting one in two million people. It is more common in females than in males. There are several hundred cases in the United States, 25 known cases in the United Kingdom, and less than that in Australia and New Zealand.