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.

The clinical course of BVVL can vary from one patient to another. There have been cases with progressive deterioration, deterioration followed by periods of stabilization, and deterioration with abrupt periods of increasing severity.

The syndrome has previously been considered to have a high mortality rate but the initial response of most patients to the Riboflavin protocol are very encouraging and seem to indicate a significantly improved life expectancy could be achievable. There are three documented cases of BVVL where the patient died within the first five years of the disease. On the contrary, most patients have survived more than 10 years after the onset of their first symptom, and several cases have survived 20–30 years after the onset of their first symptom.

Families with multiple cases of BVVL and, more generally, multiple cases of infantile progressive bulbar palsy can show variability in age of disease onset and survival. Dipti and Childs described such a situation in which a family had five children that had Infantile PBP. In this family, three siblings showed sensorineural deafness and other symptoms of BVVL at an older age. The other two siblings showed symptoms of Fazio-Londe disease and died before the age of two.

Response to treatment is variable and the long-term and functional outcome is unknown. To provide a basis for improving the understanding of the epidemiology, genotype/phenotype correlation and outcome of these diseases their impact on the quality of life of patients, and for evaluating diagnostic and therapeutic strategies a patient registry was established by the noncommercial International Working Group on Neurotransmitter Related Disorders (iNTD).

As of 2015, there are approximately 70 known cases of Brown-Vialetto-Van-Laere syndrome worldwide. BVVL was first described in a Portuguese family, and has since been described in a number of ethnic groups. Reports have shown that BVVL infects females more than males at a rate of 5:1 respectively. However, males usually exhibit more severe symptoms, an earlier onset of deafness and a tendency to die earlier in life.

Kufor–Rakeb syndrome is an autosomal recessive disorder of juvenile onset also known as Parkinson disease-9 (PARK9).

Symptoms include supranuclear gaze palsy, spasticity, and dementia.

It can be associated with "ATP13A2". It is named after Kufr Rakeb in Irbid, Jordan.

There is currently no effective treatment or cure for PSP, although some of the symptoms can respond to nonspecific measures. The average age at symptoms onset is 63 and survival from onset averages 7 years with a wide variance. Pneumonia is a frequent cause of death.

Fazio–Londe disease is linked to a genetic mutation in the "SLC52A3" gene on chromosome 20 (locus: 20p13). It is allelic and phenotypically similar to Brown–Vialetto–Van Laere syndrome.

The condition is inherited in an autosomal recessive manner.

The gene encodes the intestinal riboflavin transporter (hRFT2).

Sneddon's syndrome is a rare condition that is usually misdiagnosed. It occurs in families and may be inherited in an autosomal dominant fashion. Sneddon's Syndrome most often becomes apparent in women in their thirties, though cases do occur in men and in children. Generally, Livedo precedes cerebrovascular involvement by roughly ten years, and many years of cerebrovascular involvement precede the development of dementia, when it occurs.

Worster-Drought syndrome is a form of congenital suprabulbar paresis that occurs in some children with cerebral palsy. It is caused by inadequate development of the corticobulbar tracts and causes problems with the mouth and tongue including impaired swallowing. A similar syndrome in adults is called anterior opercular syndrome.

A 1986 study of a family in which multiple members had Worster-Drought Syndrome suggested it might be hereditary.

A 2000 review of cases classified Worster-Drought Syndrome as a form of cerebral palsy, caused by early damage to the brain, but identified no obvious causes during gestation or birth and found some families with a history of the condition.

The syndrome was named after Cecil Charles Worster-Drought, the doctor who discovered it in 1956.

The cause of PSP is unknown. Fewer than 1% of those with PSP have a family member with the same disorder. A variant in the gene for tau protein called the H1 haplotype, located on chromosome 17, has been linked to PSP. Nearly all people with PSP received a copy of that variant from each parent, but this is true of about two-thirds of the general population. Therefore, the H1 haplotype appears to be necessary but not sufficient to cause PSP. Other genes, as well as environmental toxins, are being investigated as other possible contributors to the cause of PSP.

Onset of first symptom has been reported between 1–12 years, with a mean age of onset at 8 years. Clinical course can be divided into early (< 6 yrs age, predominance of respiratory symptoms) and late course (6–20 years of age, predominance of motor symptoms on superior limbs). Progression to involve other cranial nerve muscles occurs over a period of months or years. In the Gomez review facial nerve was affected in all cases while hypoglossal nerve was involved in all except one case. Other cranial nerves involved were vagus, trigeminal, spinal accessory nerve, abducent, occulomotor and glossopharyngeal in this order. Corticospinal tract signs were found in 2 of the 14 patients.

The disease may progress to patient's death in a period as short as 9 months or may have a slow evolution or may show plateaus. Post mortem examination of cases have found depletion of nerve cells in the nuclei of cranial nerves. The histologic alterations found in patient with Fazio–Londe disease were identical to those seen in infantile-onset spinal muscular atrophy.

Strength may improve with administration of cholinesterase inhibitors.

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.

In the United States, sarcoidosis has a prevalence of approximately 10 cases per 100,000 whites and 36 cases per 100,000 blacks. Heerfordt syndrome is present in 4.1–5.6% of those with sarcoidosis.

Clinical presentation of CBD usually does not occur until age 60, with the earliest recorded diagnosis and subsequent postmortem verification being age 28. Although men and women present with the disease, some analysis has shown a predominant appearance of CBD in women. Current calculations suggest that the prevalence of CBD is approximately 4.9 to 7.3 per 100,000 people. The prognosis for an individual diagnosed with CBD is death within approximately eight years, although some patients have been diagnosed over 17 years ago (2017) and are still in relatively good standing, but with serious debilitation such as dysphagia, and overall limb rigidity. The partial (or total) use of a feeding tube may be necessary and will help prevent aspiration pneumonia, primary cause of death in CBD. Incontinence is common, as patients often can't express their need to go, due to eventual loss of speech. Therefore, proper hygiene is mandatory to prevent urinary tract infections.

Although HSP is a progressive condition, the prognosis for individuals with HSP varies greatly. It primarily affects the legs although there can be some upperbody involvement in some individuals. Some cases are seriously disabling while others are less disabling and are compatible with a productive and full life. The majority of individuals with HSP have a normal life expectancy.

Parkinson-plus syndromes, also known as disorders of multiple system degeneration, is a group of neurodegenerative diseases featuring the classical features of Parkinson's disease (tremor, rigidity, akinesia/bradykinesia, and postural instability) with additional features that distinguish them from simple idiopathic Parkinson's disease (PD). Some consider Alzheimer's disease to be in this group. Parkinson-plus syndromes are either inherited genetically or occur sporadically.

The atypical parkinsonian or Parkinson-plus syndromes are often difficult to differentiate from PD and each other. They include multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). Dementia with Lewy bodies (DLB), may or may not be part of the PD spectrum, but it is increasingly recognized as the second-most common type of neurodegenerative dementia after Alzheimer's disease. These disorders are currently lumped into two groups, the synucleinopathies and the tauopathies. They may coexist with other pathologies.

Additional Parkinson-plus syndromes include Pick's disease and olivopontocerebellar atrophy. The latter is characterized by ataxia and dysarthria, and may occur either as an inherited disorder or as a variant of multiple system atrophy. MSA is also characterized by autonomic failure, formerly known as Shy–Drager syndrome.

Clinical features that distinguish Parkinson-plus syndromes from idiopathic PD include symmetrical onset, a lack of or irregular resting tremor, and a reduced response to dopaminergic drugs (including levodopa). Additional features include bradykinesia, early-onset postural instability, increased rigidity in axial muscles, dysautonomia, alien limb syndrome, supranuclear gaze palsy, apraxia, involvement of the cerebellum including the pyramidal cells, and in some instances significant cognitive impairment.

Kearns–Sayre syndrome occurs spontaneously in the majority of cases. In some cases it has been shown to be inherited through mitochondrial, autosomal dominant, or autosomal recessive inheritance. There is no predilection for race or sex, and there are no known risk factors. As of 1992 there were only 226 cases reported in published literature.

Infantile Progressive Bulbar palsy is a rare type of progressive bulbar palsy that occurs in children. The disease exists in both rapid and slow onsets, and involves inflammation of the gray matter of the bulb. Infantile PBP is a disease that manifests itself in two forms: Fazio Londe syndrome (FL) and Brown-Vialetto-Van-Laere syndrome (BVVL).

Frontotemporal lobar degeneration (FTLD) is a pathological process that occurs in frontotemporal dementia. It is characterized by atrophy in the frontal lobe and temporal lobe of the brain, with sparing of the parietal and occipital lobes.

Common proteinopathies that are found in FTLD include the accumulation of Tau proteins and TARDBPs. Mutations in the C9orf72 gene have been established as a major genetic contribution of FTLD, although defects in the GRN and MAPT genes are also associated with it.

CADASIL or CADASIL syndrome, involving cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, is the most common form of hereditary stroke disorder, and is thought to be caused by mutations of the "Notch 3" gene on chromosome 19. The disease belongs to a family of disorders called the leukodystrophies. The most common clinical manifestations are migraine headaches and transient ischemic attacks or strokes, which usually occur between 40 and 50 years of age, although MRI is able to detect signs of the disease years prior to clinical manifestation of disease.

Foville's syndrome is caused by the blockage of the perforating branches of the basilar artery in the region of the brainstem known as the pons. Most frequently caused by vascular disease or tumors involving the dorsal pons.[3]

Structures affected by the infarct are the PPRF, nuclei of cranial nerves VI and VII, corticospinal tract, medial lemniscus, and the medial longitudinal fasciculus. There's involvement of the fifth to eighth cranial nerves, central sympathetic fibres (Horner syndrome) and horizontal gaze palsy.[3]

An effective treatment has yet to be found. In many cases electrical stimulation of the globus pallidus has been shown to produce improvement of dystonia severity, however it has not been shown to delay neurodegeneration. There is often overlap in the phenotypes of the symptoms both between different NBIA disorders and between NBIA and other disorders, leading to misdiagnoses. Treatments typically treat or ameliorate the symptoms and do not address the accumulation of iron. Psychotherapy, such as dopaminergic drugs, anticholinergics, tetrabenazine, is often used to treat the symptoms but does not improve the long term outcome of the patient.

The group includes the following disorders:

- Pantothenate kinase-associated neurodegeneration (PKAN) also known as neurodegeneration with brain iron accumulation 1 (NBIA1) and Hallervorden–Spatz syndrome

- PLAN (PLA2G6-associated neurodegeneration)

- MPAN (Mitochondrial membrane protein-associated neurodegeneration)

- BPAN (Beta-propeller protein-associated neurodegeneration)

- FAHN (Fatty acid hydroxylase-associated neurodegeneration)

- Kufor–Rakeb syndrome

- Neuroferritinopathy

- Aceruloplasminemia

- Woodhouse–Sakati syndrome

- CoPAN (CoA synthase protein-associated neurodegeneration)

- Idiopathic NBIA

- Neurodegeneration with brain iron accumulation 2B (NBIA2B)

- Neurodegeneration with brain iron accumulation 3 (NBIA3)

HSP is a group of genetic disorders. It follows general inheritance rules and can be inherited in an autosomal dominant, autosomal recessive or X-linked recessive manner. The mode of inheritance involved has a direct impact on the chances of inheriting the disorder. Over 70 genotypes had been described, and over 50 genetic loci have been linked to this condition. Ten genes have been identified with autosomal dominant inheritance. One of these SPG4 accounts for ~50% of all genetically solved cases cases, or approximately 25% of all HSP cases. Twelve genes are known to be inherited in an autosomal recessive fashion. Collectively this latter group account for ~1/3 cases.

Most altered genes have known function, but for some the function haven’t been identified yet. All of them are listed in the gene list below, including their mode of inheritance. Some examples are spastin (SPG4) and paraplegin (SPG7) are both AAA ATPases.

Currently there is no curative treatment for KSS. Because it is a rare condition, there are only case reports of treatments with very little data to support their effectiveness. Several promising discoveries have been reported which may support the discovery of new treatments with further research. Satellite cells are responsible for muscle fiber regeneration. It has been noted that mutant mtDNA is rare or undetectable in satellite cells cultured from patients with KSS. Shoubridge et al. (1997) asked the question whether wildtype mtDNA could be restored to muscle tissue by encouraging muscle regeneration. In the forementioned study, regenerating muscle fibers were sampled at the original biopsy site, and it was found that they were essentially homoplasmic for wildtype mtDNA. Perhaps with future techniques of promoting muscle cell regeneration and satellite cell proliferation, functional status in KSS patients could be greatly improved.

One study described a patient with KSS who had reduced serum levels of coenzyme Q10. Administration of 60–120 mg of Coenzyme Q10 for 3 months resulted in normalization of lactate and pyruvate levels, improvement of previously diagnosed first degree AV block, and improvement of ocular movements.

A screening ECG is recommended in all patients presenting with CPEO. In KSS, implantation of pacemaker is advised following the development of significant conduction disease, even in asymptomatic patients.

Screening for endocrinologic disorders should be performed, including measuring serum glucose levels, thyroid function tests, calcium and magnesium levels, and serum electrolyte levels. Hyperaldosteronism is seen in 3% of KSS patients.

Sneddon's patients are generally treated with warfarin, maintaining a high INR of 3-4. Because most will experience significant relief of symptoms after several months of consistent INR in this range, treatment with warfarin is often used as a diagnostic tool.