DM1 is the most common form of myotonic muscular dystrophy diagnosed in children, with a prevalence ranging from 1 per 100,000 in Japan to 3-15 per 100,000 in Europe. The prevalence may be as high as 1 in 500 in regions such as Quebec, possibly due to the founder effect. In most populations, DM1 appears to be more common than DM2. However, recent studies suggest that type 2 may be as common as type 1 among people in Germany and Finland.

The incidence of congenital myotonic dystrophy is thought to be about 1:20,000. DM occurs in about 1 per 7,000–8,000 people and has been described in people from all over the world. It affects males and females approximately equally. About 30,000 people in the United States are affected.

Myotonic dystrophy is a genetic condition which is inherited in an autosomal dominant pattern and thus will be passed along to 50% of a carrier's offspring, on average. Myotonic dystrophy is one of several known trinucleotide repeat disorders. Certain areas of DNA have repeated sequences of two or three nucleotides.

Myotonic dystrophy (DM) is an inherited disease. A severe form of DM, congenital myotonic dystrophy, may appear in newborns of mothers who have DM. Congenital myotonic dystrophy can also be inherited via the paternal gene, although it is said to be relatively rare. Congenital means that the condition is present from birth.

The progression of Becker muscular dystrophy is highly variable—much more so than Duchenne muscular dystrophy. There is also a form that may be considered as an intermediate between Duchenne and Becker MD (mild DMD or severe BMD).

Severity of the disease may be indicated by age of patient at the onset of the disease. One study showed that there may be two distinct patterns of progression in Becker muscular dystrophy. Onset at around age 7 to 8 years of age shows more cardiac involvement and trouble climbing stairs by age 20, if onset is around age 12, there is less cardiac involvement.

The quality of life for patients with Becker muscular dystrophy can be impacted by the symptoms of the disorder. But with assistive devices, independence can be maintained. People affected by Becker muscular dystrophy can still maintain active lifestyles.

These conditions are generally inherited, and the different muscular dystrophies follow various inheritance patterns. Muscular dystrophy can be inherited by individuals as an X-linked disorder, a recessive or dominant disorder. Furthermore, it can be a spontaneous mutation which means errors in the replication of DNA and spontaneous lesions. Spontaneous lesions are due to natural damage to DNA, where the most common are depurination and deamination.

Dystrophin protein is found in muscle fibre membrane; its helical nature allows it to act like a spring or shock absorber. Dystrophin links actin in the cytoskeleton and dystroglycans of the muscle cell plasma membrane, known as the sarcolemma (extracellular). In addition to mechanical stabilization, dystrophin also regulates calcium levels.

Recent studies on the interaction of proteins with missense mutations and its neighbors showed high degree of rigidity associated with central hub proteins involved in protein binding and flexible subnetworks having molecular functions involved with calcium.

Muscular dystrophy (MD) is a group of muscle diseases that results in increasing weakening and breakdown of skeletal muscles over time. The disorders differ in which muscles are primarily affected, the degree of weakness, how fast they worsen, and when symptoms begin. Many people will eventually become unable to walk. Some types are also associated with problems in other organs.

There are nine main categories of muscular dystrophy that contain more than thirty specific types. The most common type is Duchenne muscular dystrophy (DMD) which typically affects males beginning around the age of four. Other types include Becker muscular dystrophy, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. They are due to mutations in genes that are involved in making muscle proteins. This can occur due to either inheriting the defect from one's parents or the mutation occurring during early development. Disorders may be X-linked recessive, autosomal recessive, or autosomal dominant. Diagnosis often involves blood tests and genetic testing.

There is no cure for muscular dystrophy. Physical therapy, braces, and corrective surgery may help with some symptoms. Assisted ventilation may be required in those with weakness of breathing muscles. Medications used include steroids to slow muscle degeneration, anticonvulsants to control seizures and some muscle activity, and immunosuppressants to delay damage to dying muscle cells. Outcomes depend on the specific type of disorder.

Duchenne muscular dystrophy, which represents about half of all cases of muscular dystrophy, affects about one in 5,000 males at birth. Muscular dystrophy was first described in the 1830s by Charles Bell. The word "dystrophy" is from the Greek "dys", meaning "difficult" and "troph" meaning "nourish". Gene therapy, as a treatment, is in the early stages of study in humans.

In northern Scandinavia, the prevalence of myotonia congenita has been estimated at 1:10,000.

Myotonia congenita is estimated to affect 1 in 1,000,000 people worldwide.

There is no known cure for Becker muscular dystrophy yet. Treatment is aimed at control of symptoms to maximize the quality of life which can be measured by specific questionnaires. Activity is encouraged. Inactivity (such as bed rest) or sitting down for too long can worsen the muscle disease. Physical therapy may be helpful to maintain muscle strength. Orthopedic appliances such as braces and wheelchairs may improve mobility and self-care.

Immunosuppressant steroids have been known to help slow the progression of Becker muscular dystrophy. The drug prednisone contributes to an increased production of the protein utrophin which closely resembles dystrophin, the protein that is defective in BMD.

The cardiac problems that occur with EDMD and myotonic muscular dystrophy may require a pacemaker.

The investigational drug Debio-025 is a known inhibitor of the protein cyclophilin D, which regulates the swelling of mitochondria in response to cellular injury. Researchers decided to test the drug in mice engineered to carry MD after earlier laboratory tests showed deleting a gene that encodes cycolphilin D reduced swelling and reversed or prevented the disease’s muscle-damaging characteristics. According to a review by Bushby, et al. if a primary protein is not functioning properly then maybe another protein could take its place by augmenting it. Upregulation of compensatory proteins has been done in models of transgenic mice.

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.

Sodium channel myotonias (SCN4A)

- Potassium-aggravated myotonia (acetazolamide responsive myotonia)

- Paramyotonia congenita

- Hyperkalemic periodic paralysis

Dystrophies

- Myotonic dystrophy (myotonic muscular dystrophy: Type 1 and Type 2)

Potassium channel disorders (KCNJ2)

- Andersen-Tawil syndrome

Other disorders

- Thyroid disorders

- Neuromyotonia (Isaacs Syndrome)

- Stiff person syndrome

- Brody myopathy (Brody Disease, Brody's Disease, Brody's Myopathy)

In infantile Krabbe disease, death usually occurs in early childhood. A 2011 study found 1, 2, 3 year survival rates of 60%, 26%, and 14%, respectively. A few survived for longer and one was still alive at age 13. Patients with late-onset Krabbe disease tend to have a slower progression of the disease and live significantly longer.

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.

Kearns–Sayre syndrome (KSS) is a mitochondrial myopathy with a typical onset before 20 years of age. KSS is a more severe syndromic variant of chronic progressive external ophthalmoplegia (abbreviated CPEO), a syndrome that is characterized by isolated involvement of the muscles controlling movement of the eyelid (levator palpebrae, orbicularis oculi) and eye (extra-ocular muscles). This results in ptosis and ophthalmoplegia respectively. KSS involves a combination of the already described CPEO as well as pigmentary retinopathy in both eyes and cardiac conduction abnormalities. Other symptoms may include cerebellar ataxia, proximal muscle weakness, deafness, diabetes mellitus, growth hormone deficiency, hypoparathyroidism, and other endocrinopathies. In both of these diseases, muscle involvement may begin unilaterally but always develops into a bilateral deficit, and the course is progressive. This discussion is limited specifically to the more severe and systemically involved variant.

In post-menopausal women, the walls of the vagina become thinner (atrophic vaginitis). The mechanism for the age-related condition is not yet clear, though there are theories that the effect is caused by decreases in estrogen levels. This atrophy, and that of the breasts concurrently, is consistent with the homeostatic (normal development) role of atrophy in general, as after menopause the body has no further functional biological need to maintain the reproductive system which it has permanently shut down.

One drug in test seemed to prevent the type of muscle loss that occurs in immobile, bedridden patients.

Testing on mice showed that it blocked the activity of a protein present in the muscle that is involved in muscle atrophy. However, the drug's long-term effect on the heart precludes its routine use in humans, and other drugs are being sought.

It is associated with LAMP2. The status of this condition as a GSD has been disputed.

Krabbe disease occurs in about one in 100,000 births. A higher incidence, about six in 1,000, has been reported in certain communities in Israel. Scandinavian countries have comparatively high rates of the disease, reported to be one in 50,000 births.

Although the genetic cause of Danon Disease is known, the mechanism of disease is not well understood. Danon disease involves a genetic defect (mutation) in a gene called LAMP2, which results in a change to the normal protein structure. While the function of the "LAMP2" gene is not well understood, it is known that LAMP2 protein is primarily located in small structures within cells called lysosomes.

Myostatin-related muscle hypertrophy (or myotonic hypertrophy) is a rare genetic condition characterized by reduced body fat and increased skeletal muscle size. Affected individuals have up to twice the usual amount of muscle mass in their bodies. They also tend to have increased muscle strength. Myostatin-related muscle hypertrophy is not known to cause medical problems, and affected individuals are intellectually normal. The prevalence of this condition is unknown.

Mutations in the "MSTN" gene cause myostatin-related muscle hypertrophy. The "MSTN" gene provides instructions for making a protein called myostatin, which is active in muscles used for movement (skeletal muscles) both before and after birth. This protein normally restrains muscle growth, ensuring that muscles do not grow too large. Mutations that reduce the production of functional myostatin lead to an overgrowth of muscle tissue. Myostatin-related muscle hypertrophy has a pattern of inheritance known as incomplete autosomal dominance. People with a mutation in both copies of the gene in each cell (homozygotes) have significantly increased muscle mass and strength. People with a mutation in one copy of the "MSTN" gene in each cell (heterozygotes) also have increased muscle bulk, but to a lesser degree.

Researchers at Guangzhou Institutes of Biomedicine and Health in China have edited the genome of beagles to create double the amount of muscle.

Life expectancy with Fabry disease for males was 58.2 years, compared with 74.7 years in the general population, and for females 75.4 years compared with 80.0 years in the general population, according to registry data from 2001 to 2008. The most common cause of death was cardiovascular disease, and most of those had received kidney replacements.

Sandhoff disease can be detected through the following procedures (before it is apparent through physical examination): a biopsy removing a sample of tissue from the liver, genetic testing, molecular analysis of cells and tissues (to determine the presence of a genetic metabolic disorder), enzyme assay, and occasionally a urinalysis to determine if the above-noted compounds are abnormally stored within the body. For a child to suffer from this disease, both parents must be carriers, and both must transmit the mutation to the child. Thus, even in the case where both parents have the mutation, there is only a 25 percent chance their child will inherit the condition. Frequently, parents are given the opportunity to have a DNA screening if they are at high risk, to determine their carrier status before they have children. However, it is also highly recommended to undergo testing even for those parents who do not have a family history of Sandhoff disease. Over 95% of the families that have children with Sandhoff disease had no known prior family history of the condition, as the mutation in the HEXB gene is "silent," or recessive, and often passed undetected from one generation to the next Naturally, if an individual carries the mutation, he or she has a risk of transmitting it to the unborn child. Genetic counseling is recommended for those who have the mutation.

The most well known laboratory to perform the blood tests is through Lysosomal Diseases Testing Laboratory, Jefferson University with Dr. Wenger. Dr. Wenger’s laboratory does testing for all lysosomal diseases including Sandhoff and Tay-Sachs. They test for build-up of certain toxins in the body as well as a low count of enzymes.

It is possible for parents who are about to have a child or had a child with Sandhoff Disease can have a PGD or PEGD. PEGD is pre-embryonic genetic diagnosis for the parents that would not benefit from a pre-implantation genetic diagnosis because of their religion or negative attitude for the discarding of embryos. PEGD sequences the genome of the embryo to be produced by two parents if they were to conceive a child. If the family has a history of Sandhoff disease it is recommended they have their genome sequenced to ensure they are not carriers or to sequence the genome of their child.

Currently Sandhoff disease does not have any standard treatment and does not have a cure. However, a person suffering from the disease needs proper nutrition, hydration, and maintenance of clear airways. To reduce some symptoms that may occur with Sandhoff disease, the patient may take anticonvulsants to manage seizures or medications to treat respiratory infections, and consume a precise diet consisting of puree foods due to difficulties swallowing. Infants with the disease usually die by the age of 3 due to respiratory infections. The patient must be under constant surveillance because they can suffer from aspiration or lack the ability to change from the passageway to their lungs versus their stomach and their spit travels to the lungs causing bronchopneumonia. The patient also lacks the ability to cough and therefore must undergo a treatment to shake up their body to remove the mucus from the lining of their lungs. Medication is also given to patients to lessen their symptoms including seizures.

Currently the government is testing several treatments including N-butyl-deoxynojirimycin in mice, as well as stem cell treatment in humans and other medical treatments recruiting test patients.

Fabry disease is a rare genetic disease. It is inherited in an X-linked manner. Fabry disease can cause a wide range of symptoms.

Fabry disease is a lysosomal storage disease which involves dysfunctional metabolism of sphingolipids and so is a sphingolipidosis.

The disease is named after one of its discoverers, Johannes Fabry (June 1, 1860 – June 29, 1930).

Several gene mutations have been identified in patients with camptocormia. These include the RYR1 gene in axial myopathy, the DMPK gene in myotonic dystrophy, and genes related to dysferlinopathy and Parkinson’s disease. These genes could serve as targets for gene therapy to treat the condition in the years to come.

A multitude of neurological disorders cause BSS, including motor neuron disease, CNS disorders, and early amyotrophic lateral sclerosis. Usually, the bent spine is caused by dysfunctioning extensor spinal muscles with a neurological cause.

Neurological origin BSS may also result from damage to the basal ganglia nuclei that are a part of the cerebral cortex, which play a major role in bodily positioning. Damage to this part of the brain can inhibit proper flexion and extension in the muscles necessary for maintaining an upright position. Additionally, the neurotransmitter dopamine plays a key role in the operation of basal ganglia. An abnormally low dopamine concentration, such as that associated with Parkinson’s disease, causes dysfunction in the basal ganglia and the associated muscle groups, leading to BSS. Studies have estimated the prevalence of BSS in people affected by Parkinson's to be between 3% and 18%.