The prevalence rate has been estimated to be less than 1/1,000,000 worldwide. However, it is much more common in the French-Canadian population of the Saguenay and Lac-St-Jean regions of Quebec, Canada, where it has a frequency of about 1 in 2100 in live births, and a carrier rate of 1 in 23.

The prognosis is poor. Patients are usually wheelchair bound by their 20s and die by their 30s.

Costeff syndrome, or 3-methylglutaconic aciduria type III, is a genetic disorder caused by mutations in the "OPA3" gene. It is typically associated with the onset of visual deterioration (optic atrophy) in early childhood followed by the development of movement problems and motor disability in later childhood, occasionally along with mild cases of cognitive deficiency. The disorder is named after Hanan Costeff, the doctor who first described the syndrome in 1989.

The long-term prognosis of Costeff syndrome is unknown, though it appears to have no effect on life expectancy at least up to the fourth decade of life. However, as mentioned previously, movement problems can often be severe enough to confine individuals to a wheelchair at an early age, and both visual acuity and spasticity tend to worsen over time.

Fucosidosis is an extremely rare disorder first described in 1962 in two Italian siblings who showed progressive intellectual disability and neurological deterioration. The disease itself is extremely rare (less than 100 documented cases) only affecting 1:2,000,000, with most cases being occurring in Italy, Cuba, and the southwest U.S. The disease has three different types. Type 1 and 2 are considered severe, and Type 3 being a mild disease. Symptoms are highly variable with mild cases being able to live to within the third or fourth decade. Type 1 and 2 are both linked with mental retardation. Severe cases can develop life-threatening complications early in childhood.

Because the major accumulating glycoconjugate in fucosidosis patients is the blood group H-antigen, it is intriguing to speculate, but the evidence is not clear at this time, that blood type may affect the course of the disease.

Paramyotonia congenita is considered an extremely rare disorder, though little epidemiological work has been done. Prevalence is generally higher in European-derived populations and lower among Asians. Epidemiological estimates have been provided for the German population. There, it was estimated that the prevalence of PC is between 1:350,000 (0.00028%) and 1:180,000 (0.00056%). However, the German population of patients with PC is not uniformly distributed across the country. Many individuals with PC herald from the Ravensberg area in North-West Germany, where a founder effect seems to be responsible for most cases. The prevalence here is estimated at 1:6000 or 0.017%.

In most cases, symptoms of NF1 are mild, and individuals live normal and productive lives. In some cases, however, NF1 can be severely debilitating and may cause cosmetic and psychological issues. The course of NF2 varies greatly among individuals. In some cases of NF2, the damage to nearby vital structures, such as other cranial nerves and the brain stem, can be life-threatening. Most individuals with schwannomatosis have significant pain. In some extreme cases the pain will be severe and disabling.

Children with NF-1 can experience social problems, attention problems, social anxiety, depression, withdrawal, thought problems, somatic complaints, learning disabilities and aggressive behavior. Treatments include psychotherapy, antidepressants and cognitive behavioral therapy.

Paramyotonia congenita (as well as hyperkalemic periodic paralysis and the potassium-aggravated myotonias) is caused by mutations in a sodium channel, SCN4A. The phenotype of patients with these mutations is indicated in Table 1. These mutations affect fast inactivation of the encoded sodium channel. There are also indications that some mutations lead to altered activation and deactivation. The result of these alterations in channel kinetics is that there is prolonged inward (depolarizing) current following muscle excitation. There is also the introduction of a “window current” due to changes in the voltage sensitivity of the channel’s kinetics. These lead to a general increase in cellular excitability, as shown in figure 1.

There has been one study of a large number of patients with paramyotonia congenita. Of 26 kindreds, it found that 17 (71%) had a mutation in SCN4A while 6 (29%) had no known mutation. There is no large difference between these two groups except that patients with no known mutation have attacks precipitated less by cold but more by hunger, are much more likely to have normal muscle biopsies, and show less decreased compound muscle action potentials when compared to patients with known mutations.

NF-1 is a progressive and diverse condition, making the prognosis difficult to predict. The NF-1 gene mutations manifest the disorder differently even amongst people of the same family. This phenomenon is called variable expressivity. For example, some individuals have no symptoms, while others may have a manifestation that is rapidly more progressive and severe.

For many NF-1 patients, a primary concern is the disfigurement caused by cutaneous/dermal neurofibromas, pigmented lesions, and the occasional limb abnormalities. However, there are many more severe complications caused by NF-1, although most of them are quite rare. Many NF patients live perfectly normal and uninterrupted lives.

The specific molecular mechanism that underpins this movement disorder is not well known. However, most researchers suggest that it follows an autosomal dominant genetic inheritance pattern in which mutations in certain genes give rise to structural abnormalities in nervous system networks responsible for voluntary skeletal muscle movement, which, in turn, result in the functional movement abnormalities seen in patients. Despite being autosomal dominant, it is important to note that the disease has variable expressivity. That is, patients who have inherited a mutated dominant allele, along with their genetically affected parent, can be symptomatic or asymptomatic for CMM disorder. The genes that currently have evidence to be associated with CMM disorder include "DCC" (deleted in colorectal carcinoma), "DNAL4" (dynein axonemal light chain 4), and "RAD51 (recombination protein A)".

"DCC" encodes a receptor for "NTN1" (netrin-1), a protein thought to be responsible for axon guidance and neuronal cell migration during development. A mutation of this gene (including nonsense, splice site mutation, insertions, frameshift) has been identified as a possible cause for CMM disorder. Experiments in mice also support the claim that CMM disorder is associated with genetic mutations in "DCC". "Kanga" mice, lacking the P3 intracellular domain of the "DCC" receptor, show a hopping gait, moving their hind legs in a strictly paired fashion, as do kangaroos.

"DNAL4" encodes a component of dynein motor complex in commissural neurons of the corpus callosum. In contrast to "DCC", "DNAL4" is thought to have a recessive inheritance pattern for the CMM disorder. In CMM disorder patients, researchers found splice site mutations on "DNAL4", which caused skipping of exon 3, and thereby omission of 28 amino acids from "DNAL4" protein. This mutant "DNAL4" protein, in turn, could lead to faulty cross-hemisphere wiring, resulting in CMM.

"RAD51" maintains genome integrity by repairing DNA double-strand breaks through homologous recombination. "RAD51" heterozygous mutations, specifically premature termination codons, have been found in many CMM disorder patients through genome-wide linkage analysis and exome sequencing. In a mouse model, researchers also found "RAD51" products in corticospinal tract axons at the pyramidal decussation. They therefore suggest that "RAD51" might be a gene that, when haploinsufficient, causes CMM disorder in humans.

Despite identification of three prospective genes, no genotype-phenotype correlations have yet been found. That is, the severity of clinical signs and symptoms does not correlate with the type of genetic variant. Mutations in the above genes account for a total of about 35 percent of cases. Mutations in other genes that have not been identified likely account for the other cases of this disorder.

Mucolipidosis type IV is severely under-diagnosed. It is often misdiagnosed as cerebral palsy. In the Ashkenazi Jewish population there are two severe mutations with a higher carrier frequency of 1:90 to 1:100.

NF1 occurs in 1 in 3000 individuals and is equally prevalent among men and women. It is among the most common inherited nervous system disorders. Affected individuals have a 10- to 15-year reduction in life expectancy compared to the average person.

Currently, purine replacement via S-adenosylmethionine (SAM) supplementation in people with Arts syndrome appears to improve their condition. This suggests that SAM supplementation can alleviate symptoms of PRPS1 deficient patients by replacing purine nucleotides and open new avenues of therapeutic intervention. Other non-clinical treatment options include educational programs tailored to their individual needs. Sensorineural hearing loss has been treated with cochlear implantation with good results. Ataxia and visual impairment from optic atrophy are treated in a routine manner. Routine immunizations against common childhood infections and annual influenza immunization can also help prevent any secondary infections from occurring.

Regular neuropsychological, audiologic, and ophthalmologic examinations are also recommended.

Carrier testing for at-risk relatives and prenatal testing for pregnancies at increased risk are possible if the disease-causing mutation in the family is known.

Canine fucosidosis is found in the English Springer Spaniel.

Typically affecting dogs between 18 months and four years, symptoms include:

- Loss of learned behavior

- Change in temperament

- Blindness

- Loss of balance

- Deafness

- Weight loss

- From the onset, disease progress is quick and fatal.

Just like the human version, canine fucosidosis is a recessive disorder and two copies of the gene must be present, one from each parent, in order to show symptoms of the disease.

The prognosis of this developmental disorder is highly based on the underlying disorder. Cerebellar hypoplasia may be progressive or static in nature. Some cerebellar hypoplasia resulting from congenital brain abnormalities/malformations are not progressive. Progressive cerebellar hypoplasia is known for having poor prognosis, but in cases where this disorder is static, prognosis is better.

Mucolipidosis type IV (ML IV or ML4) is an autosomal recessive lysosomal storage disorder. Individuals with the disorder have many symptoms including delayed psychomotor development and various ocular aberrations. The disorder is caused by mutations in the MCOLN1 gene, which encodes a non-selective cation channel, mucolipin1. These mutations disrupt cellular functions and lead to a neurodevelopmental disorder through an unknown mechanism. Researchers dispute the physiological role of the protein product and which ion it transports.

Myotonia may present in the following diseases with different causes related to the ion channels in the skeletal muscle fiber membrane (Sarcolemma).

Two documented types, DM1 and DM2 exist. In myotonic dystrophy a nucleotide expansion of either of two genes, related to type of disease, results in failure of correct expression (splicing of the mRNA) of the ClC-1 ion channel, due to accumulation of RNA in the cytosol of the cell. The ClC-1 ion channel is responsible for the major part of chloride conductance in the skeletal muscle cell, and lack of sufficient chloride conductance may result in myotonia, (see myotonia congenita). When the splicing of the mRNA was corrected in vitro, ClC-1 channel function was greatly improved and myotonia was abolished.

HPS is one of the rare lung diseases currently being studied by The Rare Lung Diseases Consortium (RLDC). The RLDC is part of the Rare Diseases Clinical Research Network (RDCRN), an initiative of the Office of Rare Diseases Research (ORDR), of the National Center for Advancing Translational Sciences (NCATS). The RLDC is dedicated to developing new diagnostics and therapeutics for patients with rare lung diseases, through collaboration between the NIH, patient organizations and clinical investigators.

Histidinemia is a rare autosomal recessive disorder. However, histidinemia is considered the most prevalent inborn error of metabolism with a reported incidence of 1:8600 (Quebec); 1:180,000 (New York) and 1:9600 (Japan); and an average of 1:12,000 observed in the neonatal screening of over 20 million newborns.

The disorder is thought to be related to mutations in the PDE3A gene.

The course of HPS has been mild in rare instances of the disorder, however, the general prognosis is still considered to be poor.

The disease can cause dysfunctions of the lungs, intestine, kidneys, and heart. The major complication of most forms of the disorder is pulmonary fibrosis, which typically exhibits in patients ages 40–50 years. This is a fatal complication seen in many forms of HPS, and is the usual cause of death from the disorder. HPS patients who develop pulmonary fibrosis typically have type 1 or type 4.

Arts syndrome is a rare metabolic disorder that causes serious neurological problems in males due to a malfunction of the PRPP synthetase 1 enzyme. Arts Syndrome is part of a spectrum of PRPS-1 related disorders with reduced activity of the enzyme that includes Charcot–Marie–Tooth disease and X-linked non-syndromic sensorineural deafness.

Mäkelä-Bengs et al. (1997,1998) performed a genome-wide screening and linkage analysis and assigned the LCCS locus to a defined region of 9q34.