Common symptoms of the disease are weakness and atrophy in the distal muscles of the lower limbs which progresses to the hands and arms, then to the trunk, neck and face. Respiratory impairment often follows.

The incidence of this disease is not precisely known but it is considered to be rare (< 1/10 population). It has been reported in 15 families to date mostly from Canada, Finland and France.

This disease usually presents between the ages of 5 to 10 years old. The usual picture is with weakness involving the upper legs and affects activities such as running and climbing stairs. As the condition progresses, patients tend to experience weakness in their lower legs and arms. Some remain able to walk in advanced age, while others require assistance in adulthood.

The symptoms of CCD are variable, but usually involve hypotonia (decreased muscle tone) at birth, mild delay in child development (highly variable between cases), weakness of the facial muscles, and skeletal malformations such as scoliosis and hip dislocation.

Symptoms may be present at birth or may appear at any stage of life. There appears to be a growing number of people who do not become symptomatic until adulthood to middle age. While generally not progressive, again there appears to be a growing number of people who do experience a slow clinically significant progression of symptomatology. These cases may hypothetically be due to the large number of gene mutations of ryanodine receptor malfunction, and with continued research may in fact be found to be clinical variants.

The onset of this disease can begin even before birth but is more commonly in childhood or later into adult life. The progression is slow, with symptoms of weakness and walking difficulties sometimes not presenting until middle age. Early symptoms include Gower's sign ("climbing" up the thighs with the hands when rising from the floor) and tiptoe-walking caused by the beginning of contractures.

Bethlem myopathy affects about 1 in 200,000 people. Contractures of the fingers are a typical symptom of Bethlem myopathy but not of the related Ullrich's myopathy (which does include contractures of arms and legs, as does Bethlem myopathy). Serum creatine kinase is elevated in Bethlem myopathy, as there is ongoing muscle cell death. Patients with Bethlem myopathy may expect a normal life span and continued mobility into adulthood. There is currently no cure for this disorder, but the contractures of the legs can be alleviated with heel-cord surgery followed by bracing and regular physical therapy. Repeated surgeries to lengthen the heel cords may be needed as the child grows to adulthood.

Signs and symptoms include (for each of the following causes):

- Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like syndrome (MELAS)

- Varying degrees of cognitive impairment and dementia

- Lactic acidosis

- Strokes

- Transient ischemic attacks

- Hearing loss

- Weight loss

- Myoclonic epilepsy and ragged-red fibers (MERRF)

- Progressive myoclonic epilepsy

- Clumps of diseased mitochondria accumulate in muscle fibers and appear as "ragged-red fibers" when muscle is stained with modified Gömöri trichrome stain

- Short stature

- Kearns-Sayre syndrome (KSS)

- External ophthalmoplegia

- Cardiac conduction defects

- Sensorineural hearing loss

- Chronic progressive external ophthalmoplegia (CPEO)

- Progressive ophthalmoparesis

- Symptomatic overlap with other mitochondrial myopathies

Multicore myopathy, also referred to as minicore myopathy, is associated with small areas of decreased oxidative activities, resulting in areas that appear in this histology as “cores”. These appear through microscopy very similar to central core, however the cores are typically smaller in multicore myopathy. As with congenital fiber type disproportion, patients have a greater number of type 1 fibers. Overall, approximately half of diagnosed individuals report no progression of muscle weakness, while half report a very slow progression.

Congenital fiber type disproportion affects skeletal muscle, typically causing weakness in the shoulders, upper arms, thighs, and hips. Skeletal muscle is made up of two kinds of fiber, type 1 and type 2. In congenital fiber type disproportion, type 1 fibers are not only smaller but often more abundant than type 2 fibers. This leads to affected individuals being able to maintain an active lifestyle, though they usually have lower levels of stamina.

Severity with this disease varies greatly, but people typically present symptoms by the age of one. Individuals do not usually worsen with time, and cases have even been reported of improvements.

In terms of the signs (and symptoms) of oculopharyngeal muscular dystrophy would be consistent with the following:

Though the aforementioned signs/symptoms are the most common, there have been cases though rare, where the peripheral nervous system has had involvement with significant reduction of myelinated fibers

In homozygous cases, this muscular dystrophy is severe and starts earlier in the affected individuals life.

There are three major types of inheritance for this disease: Autosomal dominant, autosomal recessive and de novo.

- The most severe form is autosomal recessive and it also has the earliest onset. It usually involves all three muscle tissues and leads to cardiac and respiratory failure as well as intestinal obstruction.

- Autosomal Dominant inheritance shows a later onset and slower progression. It usually involves only one or two of the muscle tissues.

- De novo diseases occur when a new mutation arises in the person that was not inherited through either parent. This form has a wide range of symptoms and varies depending on the mutation made.

Some early signs of HIBMs includes:

- Difficulty walking on heels, and difficulty running;

- Weak index finger;

- Frequent loss of balance.

- On muscle biopsy, the typical finding includes inclusion bodies, rimmed vacuoles and accumulation of aberrant proteins similar to those found in senile plaques of Alzheimer's disease (amyloid beta, hyperphosphorylated tau, amongst others)

Physical expression of nemaline myopathy varies greatly, but weakness is usually concentrated in the proximal muscles, particularly respiratory, bulbar and trunk muscles. People with severe NM show obvious symptoms at birth, while those with intermediate or mild NM may initially appear unaffected. Babies with NM are frequently observed to be "floppy" and hypotonic. Children born with NM often gain strength as they grow, though the effect of muscle weakness on body features may become more evident with time. Adults with NM typically have a very slender physique.

Bulbar (throat) muscle weakness is a main feature of nemaline myopathy. Most individuals with severe NM are unable to swallow and receive their nutrition through feeding tubes. Most people with intermediate and mild NM take some or all of their nutrition orally. Bulbar muscle impairment may also lead to difficulty with communication. People with NM often have hypernasal speech as a result of poor closure of the velopharyngeal port (between the soft palate and the back of the throat). Communicative skills may be enhanced through speech therapy, oral prosthetic devices, surgery, and augmentative communication devices. Individuals with NM are usually highly sociable and intelligent, with a great desire to communicate.

Hereditary inclusion body myopathies (HIBM) are a heterogeneous group of very rare genetic disorders which have different symptoms. Generally, they are neuromuscular disorders characterized by muscle weakness developing in young adults. Hereditary inclusion body myopathies comprise both autosomal recessive and autosomal dominant muscle disorders that have a variable expression (phenotype) in individuals, but all share similar structural features in the muscles.

HIBMs are a group of muscle wasting disorders, which are uncommon in the general world population. One autosomal recessive form of HIBM is known as IBM2 or GNE myopathy, which is a common genetic disorder amongst people of Iranian Jewish descent. IBM2 has also been identified in other minorities throughout the world, including people of Asian (Japanese and others), European, and South American origin, as well as Muslim people in the Middle Eastern, Palestinian, and Iranian origin. In Japan and many East Asian countries, this disorder is known as Distal Myopathy with Rimmed Vacuoles (DMRV).

IBM2 causes progressive muscle weakness and wasting. Muscle wasting usually starts around the age of 20 – 30 years, although young onset at 17 and old onset at 52 has been recorded. As such, it affects the most productive times of our lives. It can progress to marked disability within 10 – 15 years, confining many people with IBM2 to a wheelchair. The weakness and severity can vary from person to person. In some, weakness in the legs is noticed first. In few others, the hands are weakened more rapidly than the legs. Weakness is progressive, which means the muscle becomes weaker over time. IBM2 does not seem to affect the brain, internal organs or sensation. The quadriceps are relatively spared, and remain strong until the late stages of disease, which is the reason IBM2 is often referred to as Quadriceps Sparing Myopathy (QSM).

Centronuclear myopathies (CNM) are a group of congenital myopathies where cell nuclei are abnormally located in skeletal muscle cells. In CNM the nuclei are located at a position in the center of the cell, instead of their normal location at the periphery.

Symptoms of CNM include severe hypotonia, hypoxia-requiring breathing assistance, and scaphocephaly. Among centronuclear myopathies, the X-linked myotubular myopathy form typically presents at birth, and is thus considered a congenital myopathy. However, some centronuclear myopathies may present later in life.

X-linked myopathy with excessive autophagy (XMEA) is a rare childhood onset disease characterized by slow progressive vacuolation and atrophy of skeletal muscle. There is no known cardiac or intellectual involvement.

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.

Bethlem myopathy is an autosomal dominant myopathy, classified as a congenital form of muscular dystrophy, that is caused by a mutation in one of the three genes coding for type VI collagen. These include COL6A1, COL6A2, and COL6A3.

As with other myopathies, the clinical manifestations of MTM/CNM are most notably muscle weakness and associated disabilities. Congenital forms often present with neonatal low muscle tone, severe weakness, delayed developmental milestones (particularly gross motor milestones such as head control, crawling, and walking) and pulmonary complications (presumably due to weakness of the muscles responsible for respiration). While some patients with centronuclear myopathies remain ambulatory throughout their adult life, others may never crawl or walk and may require wheelchair use for mobility. There is substantial variability in the degree of functional impairment among the various centronuclear myopathies. Although this condition only affects the voluntary muscles, several children have suffered from cardiac arrest, possibly due to the additional stress placed on the heart.

Other observed features have been high arched palate, long digits, bell shaped chest and long face.

Myotubular myopathy only affects muscles and does not impact intelligence in any shape or form.

X-linked myotubular myopathy was traditionally a fatal condition of infancy, with life expectancy of usually less than two years. There appears to be substantial variability in the clinical severity for different genetic abnormalities at that same MTM1 gene. Further, published cases show significant differences in clinical severity among relatives with the same genetic abnormality at the MTM1 gene. Most truncating mutations of MTM1 cause a severe and early lethal phenotype, while some missense mutations are associated with milder forms and prolonged survival (up to 54 years).

Centronuclear myopathies typically have a milder presentation and a better prognosis. Recently, researchers discovered mutations at the gene dynamin 2 (DNM2 on chromosome 19, at site 19p13.2), responsible for the autosomal dominant form of centronuclear myopathy. This condition is now known as dynamin 2 centronuclear myopathy (abbreviated DNM2-CNM). Research has indicated that patients with DNM2-CNM have a slowly progressive muscular weakness usually beginning in adolescence or early adulthood, with an age range of 12 to 74 years.

Mitochondrial myopathies are types of myopathies associated with mitochondrial disease. On biopsy, the muscle tissue of patients with these diseases usually demonstrate "ragged red" muscle fibers. These ragged-red fibers contain mild accumulations of glycogen and neutral lipids, and may show an increased reactivity for succinate dehydrogenase and a decreased reactivity for cytochrome c oxidase. Inheritance was believed to be maternal (non-Mendelian extranuclear). It is now known that certain nuclear DNA deletions can also cause mitochondrial myopathy such as the OPA1 gene deletion. There are several subcategories of mitochondrial myopathies.

Patients usually begin to notice symptoms in their 50s and the course is usually slowly progressive. Common features include peripheral neuropathy, cardiomyopathy, and hemolytic anemia. Other features include limb chorea, facial tics, other oral movements (lip and tongue biting), seizures, a late-onset dementia, and behavioral changes.

The prolonged muscle contractions, which occur most commonly in the leg muscles in recessive mutations, and more commonly in the hands, face, and eyelids in dominant mutations, are often enhanced by inactivity, and in some forms are relieved by repetitive movement known as "the warm-up effect". This effect often diminishes quickly with rest. Some individuals with myotonia congenita are prone to falling as a result of hasty movements or an inability to stabilize themselves after a loss of balance. During a fall, a person with myotonia congenita may experience partial or complete rigid paralysis that will quickly resolve once the event is over. However, a fall into cold water may render the person unable to move for the duration of submergence. As with myotonic goats, children are more prone to falling than adults, due to their impulsivity.

The two major types of myotonia congenita are distinguished by the severity of their symptoms and their patterns of inheritance. Becker disease usually appears later in childhood than Thomsen disease, and causes more severe myotonia, muscle stiffness and transient weakness. Although myotonia in itself is not normally associated with pain, cramps or myalgia may develop. People with Becker disease often experience temporary attacks of muscle weakness, particularly in the arms and hands, brought on by movement after periods of rest. They may also develop mild, permanent muscle weakness over time. This muscle weakness is not observed in people with Thomsen disease. However, in recent times, as more of the individual mutations that cause myotonia congenita are identified, these limited disease classifications are becoming less widely used.

Early symptoms in a child may include:

- Difficulty swallowing

- Gagging

- Stiff movements that improve when they are repeated

- Frequent falling

- Difficulties opening eyelids after strenuous contraction or crying (von Graefe's sign)

Possible complications may include:

- Aspiration pneumonia (caused by swallowing difficulties)

- Frequent choking or gagging in infants (also caused by swallowing difficulties)

- Abdominal muscle weakness

- Chronic joint problems

- Injury due to falls

Distal muscular dystrophy (or distal myopathy) is a group of disorders characterized by onset in the hands or feet. Many types involve dysferlin, but it has been suggested that not all cases do.

Types include:

DYSF is also associated with limb-girdle muscular dystrophy type 2B.

Distal muscular dystrophy is a type of muscular dystrophy that affects the muscles of the extremities, the hands, feet, lower arms, or lower legs. The cause of this dystrophy is very hard to determine because it can be a mutation in any of at least eight genes and not all are known yet. These mutations can be inherited from one parent, autosomal dominant, or from both parents, autosomal recessive. Along with being able to inherit the mutated gene, distal muscular dystrophy has slow progress therefore the patient may not know that they have it until they are in their late 40’s or 50’s. There are eight known types of distal muscular dystrophy. They are Welander’s distal myopathy, Finnish (tibial) distal myopathy, Miyoshi distal myopathy, Nonaka distal myopathy, Gowers–Laing distal myopathy, hereditary inclusion-body myositis type 1, distal myopathy with vocal cord and pharyngeal weakness, and ZASP-related myopathy. All of these affect different regions of the extremities and can show up as early as 5 years of age to as late as 50 years old. Doctors are still trying to determine what causes these mutations along with effective treatments.

Patients with CED complain of chronic bone pain in the legs or arms, muscle weakness (myopathy) and experience a waddling gait. Other clinical problems associated with the disease include increased fatigue, weakness, muscle spasms, headache, difficulty gaining weight, and delay in puberty. Some patients have an abnormal or absent tibia, may present with a flat foot, or scoliosis.

This disease may also cause bones to become abnormally hardened which is referred to as sclerosis. This hardening may affect the bones at the base of the skull or those in the hands, feet, or jaw. This causes ongoing pain and aching within the body parts that are affected. The pain has been described as either a hot electric stabbing pain, an ever-increasing pressure sensation around the bones (especially before electrical storms) or as a constant ache that radiates through several long bones at once. Pain may also occur in the hips, wrists, knees and other joints as they essentially just 'lock-up' (often becoming very stiff, immobile and sore), mostly when walking up or down staircases, writing for extended periods of time, or during the colder months of the year. Those with the disease tend to have a very characteristic walk medically diagnosed as a 'waddling gait'. This is observed by the broad-based gait with a duck-like waddle to the swing phase, the pelvis drops to the side of the leg being raised, notable forward curvature of the lumbar spine and a marked body swing.

The pain is especially severe during a 'flare-up', these can be unpredictable, exhausting and last anywhere from a few hours to several weeks. This is a common occurrence for several CED patients, often causing myopathy and extensive sleep deprivation from the chronic, severe and disabling pain. Patients may even require the use of a wheelchair (or additional carer's help with getting dressed, showering, mobility/shopping, preparing meals or lifting heavy items) especially when bedridden or housebound for days or weeks at a time. 'Flare-ups' may be attributed to, or exacerbated by growth spurts, stress, exhaustion, exercise, standing or walking for too long, illness, infection, being accidentally knocked/hurt or injured, after surgery/anaesthetics, cold weather, electrical storms, and sudden changes in barometric pressure.

CED may also affect internal organs, the liver and spleen, which may become enlarged. A loss of vision and/or hearing can occur if bones are adversely affected by the hardening in the skull. Hence proactive specialist check-ups, X-rays, diagnostic tests/scans, and regular blood tests are recommended on an annual basis to monitor the CED bony growth and secondary medical issues that may arise from this condition.

Oculopharyngeal muscular dystrophy (OPMD) is a rare form of muscular dystrophy with symptoms generally starting when an individual is 40 to 50 years old. It can be autosomal dominant neuromuscular disease or autosomal recessive. The most common inheritance of OPMD is autosomal dominant, which means only one copy of the mutated gene needs to be present in each cell. Children of an affected parent have a 50% chance of inheriting the mutant gene.

Autosomal dominant inheritance is the most common form of inheritance. Less commonly, OPMD can be inherited in an autosomal recessive pattern, which means that two copies of the mutated gene need to be present in each cell, both parents need to be carriers of the mutated gene, and usually show no signs or symptoms. The PABPN1 mutation contains a GCG trinucleotide repeat at the 5' end of the coding region, and expansion of this repeat which then leads to autosomal dominant oculopharyngeal muscular dystrophy (OPMD) disease.

MELAS is a condition that affects many of the body's systems, particularly the brain and nervous system (encephalo-) and muscles (myopathy). In most cases, the signs and symptoms of this disorder appear in childhood following a period of normal development. Early symptoms may include muscle weakness and pain, recurrent headaches, loss of appetite, vomiting, and seizures. Most affected individuals experience stroke-like episodes beginning before age 40. These episodes often involve temporary muscle weakness on one side of the body (hemiparesis), altered consciousness, vision abnormalities, seizures, and severe headaches resembling migraines. Repeated stroke-like episodes can progressively damage the brain, leading to vision loss, problems with movement, and a loss of intellectual function (dementia). The stroke-like episodes can be mis-diagnosed as epilepsy by a doctor not aware of the MELAS condition.

Most people with MELAS have a buildup of lactic acid in their bodies, a condition called lactic acidosis. Increased acidity in the blood can lead to vomiting, abdominal pain, extreme tiredness (fatigue), muscle weakness, loss of bowel control, and difficulty breathing. Less commonly, people with MELAS may experience involuntary muscle spasms (myoclonus), impaired muscle coordination (ataxia), hearing loss, heart and kidney problems, diabetes, epilepsy, and hormonal imbalances.

The presentation of some cases is similar to that of Kearns-Sayre syndrome.