The cause of de Quervain's disease is not established. Evidence regarding a possible relation with occupational risk factors is debated. A systematic review of potential risk factors discussed in the literature did not find any evidence of a causal relationship with occupational factors. However, researchers in France found personal and work-related factors were associated with de Quervain's disease in the working population; wrist bending and movements associated with the twisting or driving of screws were the most significant of the work-related factors. Proponents of the view that De Quervain syndrome is a repetitive strain injury consider postures where the thumb is held in abduction and extension to be predisposing factors. Workers who perform rapid repetitive activities involving pinching, grasping, pulling or pushing have been considered at increased risk. Specific activities that have been postulated as potential risk factors include intensive computer mouse use, trackball use, and typing, as well as some pastimes, including bowling, golf, fly-fishing, piano-playing, sewing, and knitting.

Women are affected more often than men. The syndrome commonly occurs during and after pregnancy. Contributory factors may include hormonal changes, fluid retention and—more debatably—lifting.

Workers in certain fields are at risk of repetitive strains. Most occupational injuries are musculoskeletal disorders, and many of these are caused by cumulative trauma rather than a single event. Miners and poultry workers, for example, must make repeated motions which can cause tendon, muscular, and skeletal injuries.

De Quervain syndrome involves noninflammatory thickening of the tendons and the synovial sheaths that the tendons run through. The two tendons concerned are those of the extensor pollicis brevis and abductor pollicis longus muscles. These two muscles run side by side and function to bring the thumb away from the hand; the extensor pollicis brevis brings the thumb outwards radially, and the abductor pollicis longus brings the thumb forward away from the palm. De Quervain tendinopathy affects the tendons of these muscles as they pass from the forearm into the hand via a fibro-osseous tunnel (the first dorsal compartment).

Evaluation of histopathological specimens shows a thickening and myxoid degeneration consistent with a chronic degenerative process, as opposed to inflammation. The pathology is identical in de Quervain seen in new mothers.

Several risk factors of CMC OA of the thumb are known. Each of these risk factors does not cause CMC OA by itself, but acts as a predisposing factor influencing the process of OA in some way. Risk factors include: female gender, suffering from obesity, repetitive heavy manual labor, familial predisposition and hormonal changes, such as menopause.

CMC OA is the most common form of OA affecting the hand. Dahaghin et al. showed that about 15% of women and 7% of men between 50 and 60 years of age suffer from CMC OA of the thumb. However, in about 65% of people older than 55 years, radiologic evidence of OA was present without any symptoms. Armstrong et al. reported a prevalence of 33% in postmenopausal women, of which one third was symptomatic, compared to 11% in men older than 55 years. This shows CMC OA of the thumb is significantly more prevalent in women, especially in postmenopausal women, compared to men.

Repetitive strain injury (RSI) and associative trauma orders are umbrella terms used to refer to several discrete conditions that can be associated with repetitive tasks, forceful exertions, vibrations, mechanical compression, or sustained/awkward positions. Examples of conditions that may sometimes be attributed to such causes include edema, tendinosis (or less often tendinitis), carpal tunnel syndrome, cubital tunnel syndrome, De Quervain syndrome, thoracic outlet syndrome, intersection syndrome, golfer's elbow (medial epicondylitis), tennis elbow (lateral epicondylitis), trigger finger (so-called stenosing tenosynovitis), radial tunnel syndrome, ulnar tunnel syndrome, and focal dystonia.

Since the 1970s there has been a worldwide increase in RSIs of the arms, hands, neck, and shoulder attributed to the widespread use of typewriters/computers in the workplace that require long periods of repetitive motions in a fixed posture.

Tenosynovitis most commonly results from the introduction of bacteria into a sheath through a puncture or laceration wound, though bacteria can also be spread from adjacent tissue or via hematogenous spread. The clinical presentation is therefore as acute infection following trauma. The infection can be mono- or polymicrobial and can vary depending on the nature of the trauma. The most common pathogenic agent is staphylococcus aureus introduced from the skin. Other bacteria linked to infectious tenosynovitis include Pasteurella multocida (associated with animal bites), Eikenella spp. (associated with IV drug use), and Mycobacterium marinum (associated with wounds exposed to fresh or salt water). Additionally, sexually active patients are at risk for hematogenous spread due to Neisseria gonorrhea (see infectious arthritis).

Noninfectious tenosynovitis can arise from overuse or secondary to other systemic inflammatory conditions such as [rheumatoid arthritis] or [reactive arthritis]. If left untreated, the tendons may undergo stenosis, causing conditions such as de Quervain’s and trigger finger.

Treatment for infectious tenosynovitis is more effective the earlier the condition is identified and treated. Factors that worsen patient outcomes include being older than 43, having diabetes mellitus, and a polymicrobial infection.

The life span in patients with Schnitzler syndrome has not been shown to differ much from the general population. Careful follow-up is advised, however. A significant proportion of patients develops a lymphoproliferative disorder as a complication, most commonly Waldenström's macroglobulinemia. This may lead to symptoms of hyperviscosity syndrome. AA amyloidosis has also been reported in people with Schnitzler syndrome.

Schnitzler syndrome is a rare disease characterised by chronic hives (urticaria) and periodic fever, bone pain and joint pain (sometimes with joint inflammation), weight loss, malaise, fatigue, swollen lymph glands and enlarged spleen and liver.

The urticarial rash is non-itching in more than half of cases, which is unusual for hives. It is most prominent on the trunk, arms and legs, sparing the palms, soles, head and neck. Associated angioedema has been reported in a few patients. A review of 94 cases found a mean age at onset of 51 years, and only four patients developed symptoms before the age of 35. The cause and disease mechanism of Schnitzler syndrome remain largely unknown.

Schnitzler syndrome is considered an autoinflammatory and autoimmune disorder. Chronic hives and a monoclonal gammopathy have been proposed as the major criteria, while the others represent minor criteria.

Respiratory complications are often cause of death in early infancy.

The first gene that could cause the syndrome is described recently and is called NF1X (chromosome 19: 19p13.1).

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

The prognosis is generally poor. With early onset, death usually occurs within 10 years from the onset of symptoms. Individuals with the infantile form usually die before the age of 7. Usually, the later the disease occurs, the slower its course is.

Alexander disease, also known as fibrinoid leukodystrophy, is a progressive and fatal neurodegenerative disease. It is a rare genetic disorder and mostly affects infants and children, causing developmental delay and changes in physical characteristics.

Facioscapulohumeral muscular dystrophy (FSHMD, FSHD or FSH)—originally named Landouzy-Dejerine—is a usually autosomal dominant inherited form of muscular dystrophy (MD) that initially affects the skeletal muscles of the face (facio), scapula (scapulo) and upper arms (humeral). FSHD is the third most common genetic disease of skeletal muscle. Orpha.net lists the prevalence as 4/100,000 while a 2014 population-based study in the Netherlands reported a significantly higher prevalence of 12 in 100,000.

Symptoms may develop in early childhood and are usually noticeable in the teenage years, with 95% of affected individuals manifesting disease by age 20 years. A progressive skeletal muscle weakness usually develops in other areas of the body as well; often the weakness is asymmetrical. Life expectancy can be threatened by respiratory insufficiency, and up to 20% of affected individuals become severely disabled, requiring use of a wheel chair or mobility scooter. In a Dutch study, approximately 1% of patients required (nocturnal or diurnal) ventilatory support. Non-muscular symptoms frequently associated with FSHD include subclinical sensorineural hearing loss and retinal telangiectasia.

In more than 95% of known cases, the disease is associated with contraction of the D4Z4 repeat in the 4q35 subtelomeric region of Chromosome 4. Seminal research published in August 2010 now shows the disease requires a second mechanism, which for the first time provides a unifying theory for its underlying genetics. The second mechanism is a "toxic gain of function" of the DUX4 gene, which is the first time in genetic research that a "dead gene" has been found to "wake up" and cause disease.

Building on the 2010 unified theory of FSHD, researchers in 2014 published the first proposed pathophysiology definition of the disease and four viable therapeutic targets for possible intervention points.

In 2007 the FSHD Global Research Foundation was established to increase the amount of funding available to research bodies. The Foundation has identified 13 priority areas of interest for FSHD research.

The vast majority of cases are due to spontaneous genetic mutations.

It can be associated with mutations affecting the cohesin complex.

Multiple genes have been associated with the condition. In 2004, researchers at the Children's Hospital of Philadelphia (United States) and the University of Newcastle upon Tyne (England) identified a gene (NIPBL) on chromosome 5 that causes CdLS when it is mutated. Since then, additional genes have been found (SMC1A, SMC3 and HDAC8) that cause CdLS when changed. There are likely other genes as well. Researchers hope to gain a better understanding of why CdLS varies so widely from one individual to another and what can be done to improve the quality of life for people with the syndrome.

The latter two genes seem to correlate with a milder form of the syndrome.

In July 2012, the fourth “CdLS gene”—HDAC8—was announced. Many parents and professionals have

questions about this latest finding and what it means. HDAC8 is an X-linked gene, meaning it is located on the X chromosome. Individuals with CdLS who have the gene change in HDAC8 make up just a small portion of all people with CdLS.

Evidence of a linkage at chromosome 3q26.3 is mixed.

Desmin-related myofibrillar myopathy is a subgroup of the myofibrillar myopathy diseases and is the result of a mutation in the gene that codes for desmin which prevents it from forming protein filaments, instead forming aggregates of desmin and other proteins throughout the cell.

De Barsy syndrome is a rare autosomal recessive genetic disorder. Symptoms include cutis laxa (loose hanging skin) as well as other eye, musculoskeletal, and neurological abnormalities. It is usually progressive, manifesting side effects that can include clouded corneas, cataracts, short stature, dystonia, or progeria (premature aging).

It was first described in 1967 by De Barsy et al. and, as of 2011, there have been 27 cases reported worldwide. The genes that cause De Barsy syndrome have not been identified yet, although several studies have narrowed down the symptoms' cause. A study by Reversade et al. has shown that a mutation in PYCR1, the genetic sequence that codes for mitochondrial enzymes that break down proline, are prevalent in cases of autosomal recessive cutis laxa (ARCL), a condition very similar to De Barsy syndrome. A study by Leao-Teles et al. has shown that De Barsy syndrome may be related to mutations in ATP6V0A2 gene, known as ATP6V0A2-CDG by the new naming system.

Alternative names for De Barsy syndrome include corneal clouding-cutis laxa-mental retardation, cutis laxa-growth deficiency syndrome, De Barsy–Moens–Diercks syndrome, and progeroid syndrome of De Barsy.

Miller syndrome is a genetic condition also known as the Genee–Wiedemann syndrome, Wildervanck–Smith syndrome, or postaxial acrofacial dystosis. The incidence of this condition is not known, but it is considered extremely rare. It is due to a mutation in the DHODH gene. Nothing is known of its pathogenesis.

This disease is endemic in Portuguese locations Póvoa de Varzim and Vila do Conde (Caxinas), with more than 1000 affected people, coming from about 500 families, where 70% of the people develop the illness. ll the analysed Portuguese families presented the same haplotype (haplotype I) associated with the Met 30 mutation. In northern Sweden, more specifically Piteå, Skellefteå and Umeå, 1.5% of the population has the mutated gene. There are many other populations in the world who exhibit the illness after having developed it independently.

The cause of alternating hemiplegia is the mutation of ATP1A3 gene. In a study of fifteen females and nine males’ patient with alternating hemiplegia, a mutation in ATP1A3 gene was present. Three patients showed heterozygous de-novo missense mutation. Six patients were found with de-novo missense mutation and one patient was identified with de-novo splice site mutation. De novo mutation is a mutation that occurs in the germ cell of one parent. Neither parent has the mutation, but it is passed to the child through the sperm or egg.

Central core disease (CCD), also known as central core myopathy, is an autosomal dominant congenital myopathy (inborn muscle disorder). It was first described by Shy and Magee in 1956. It is characterized by the appearance of the myofibril under the microscope.

Central core disease is inherited in an autosomal dominant fashion. Most cases have demonstrable mutations in the ryanodine receptor type 1 ("RYR1") gene, which are often "de novo" (newly developed). People with CCD are at risk for malignant hyperthermia (MH) when receiving general anesthesia.