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.

Congenital mirror movement disorder (CMM disorder) is a rare genetic neurological disorder which is characterized by mirrored movement, sometimes referred to as associated or synkinetic movement, most often in the upper extremity of the body. These movements are voluntary intentional movements on one, ipsilateral, side of the body that are mirrored simultaneously by involuntary movements on the contralateral side.

The reproduction of involuntary movement usually happens along the head-tail axis, having a left-right symmetry. For example, if someone were to voluntarily make a fist with their left hand, their right hand would do the same. In most cases, the accompanying contralateral involuntary movements are much weaker than the ipsilateral voluntary ones, although the extent and magnitude of the mirrored movement vary across patients. This disorder has not yet been found to be associated with any other neurologic disease or cognitive disability, and currently, no cures nor means to improve signs or symptoms have been found.

The congenital mirror movements begin in infancy and persist throughout the patient’s life, often with very little improvement, or deterioration. Consequently, patients who do suffer from this movement disorder have serious difficulty carrying out tasks that require manual dexterity or precision, such as playing a two handed musical instrument or typing on a keyboard, for their whole lives. Patients also often experience discomfort or pain in the upper limbs due to prolonged use of the same muscles. Therefore, quality of life can be severely hampered.

CMM disorder’s prevalence in the world is thought to be less than 1 in 1 million people. Because of its rarity, researchers suggest that some mildly affected individuals may never be diagnosed. It is important not to confuse congenital mirror movement disorders, a rare genetically based neurologic disease, with acquired mirror movement disorders that present themselves during one’s lifetime due to other reasons (stroke for example).

In most cases, between the age of 2 and 4 oculomotor signals are present. Between the age of 2 and 8, telangiectasias appears. Usually by the age of 10 the child needs a wheel chair. Individuals with autosomal recessive cerebellum ataxia usually survive till their 20s; in some cases individuals have survived till their 40s or 50s.

Surgery, such as the denervation of selected muscles, may also provide some relief; however, the destruction of nerves in the limbs or brain is not reversible and should be considered only in the most extreme cases. Recently, the procedure of deep brain stimulation (DBS) has proven successful in a number of cases of severe generalised dystonia. DBS as treatment for medication-refractory dystonia, on the other hand, may increase the risk of suicide in patients. However, reference data of patients without DBS therapy are lacking.

Developmental coordination disorder is a lifelong neurological condition that is more common in males than in females, with a ratio of approximately four males to every female. The exact proportion of people with the disorder is unknown since the disorder can be difficult to detect due to a lack of specific laboratory tests, thus making diagnosis of the condition one of elimination of all other possible causes/diseases. Approximately 5–6% of children are affected by this condition.

Autosomal recessive cerebellar ataxia type 1 (ARCA1) is a condition characterized by progressive problems with movement. Signs and symptoms of the disorder first appear in early to mid-adulthood. People with this condition initially experience impaired speech (dysarthria), problems with coordination and balance (ataxia), or both. They may also have difficulty with movements that involve judging distance or scale (dysmetria). Other features of ARCA1 include abnormal eye movements (nystagmus) and problems following the movements of objects with their eyes. The movement problems are slowly progressive, often resulting in the need for a cane, walker, or wheelchair.

Although not necessary for the diagnosis, individuals with intellectual disability are at higher risk for SMD. It is more common in boys, and can occur at any age.

Movement disorders are clinical syndromes with either an excess of movement or a paucity of voluntary and involuntary movements, unrelated to weakness or spasticity. Movement disorders are synonymous with basal ganglia or extrapyramidal diseases. Movement disorders are conventionally divided into two major categories- "hyperkinetic" and "hypokinetic".

Hyperkinetic movement disorders refer to dyskinesia, or excessive, often repetitive, involuntary movements that intrude upon the normal flow of motor activity.

Hypokinetic movement disorders refer to akinesia (lack of movement), hypokinesia (reduced amplitude of movements), bradykinesia (slow movement) and rigidity. In primary movement disorders, the abnormal movement is the primary manifestation of the disorder. In secondary movement disorders, the abnormal movement is a manifestation of another systemic or neurological disorder.

Treatment depends upon the underlying disorder. Movement disorders have been known to be associated with a variety of autoimmune diseases.

Almost all cases of synkinesis develop as a sequel to nerve trauma (the exception is when it is congenitally acquired as in Duane-Retraction Syndrome and Marcus Gunn phenomenon). Trauma to the nerve can be induced in cases such as surgical procedures, nerve inflammation, neuroma

, and physical injury.

Hemiplegia is not a progressive disorder, except in progressive conditions like a growing brain tumour. Once the injury has occurred, the symptoms should not worsen. However, because of lack of mobility, other complications can occur. Complications may include muscle and joint stiffness, loss of aerobic fitness, muscle spasms, bed sores, pressure ulcers and blood clots.

Sudden recovery from hemiplegia is very rare. Many of the individuals will have limited recovery, but the majority will improve from intensive, specialised rehabilitation. Potential to progress may differ in cerebral palsy, compared to adult acquired brain injury. It is vital to integrate the hemiplegic child into society and encourage them in their daily living activities. With time, some individuals may make remarkable progress.

Prognosis depends on the severity of the disorder. Recognizing symptoms early can help reduce the risk of self-injury, which can be lessened with meditations. Stereotypic movement disorder due to head trauma may be permanent.

Brain trauma in the developing human is a common cause (over 400,000 injuries per year in the US alone, without clear information as to how many produce developmental sequellae) of neurodevelopmental syndromes. It may be subdivided into two major categories, congenital injury (including injury resulting from otherwise uncomplicated premature birth) and injury occurring in infancy or childhood. Common causes of congenital injury are asphyxia (obstruction of the trachea), hypoxia (lack of oxygen to the brain) and the mechanical trauma of the birth process itself.

Synkinesis is an interaction of nerves with muscles (although glands can also be involved). Most cases involve the cranial nerves which innervate many small cranial muscles, such as the facial muscles and the extraocular muscles. This is in contrast to areas of body where miswiring of the larger muscles is less evident due the size of the muscles. Synkinesis can also involve the upper limbs, especially hands which is quite rare, at 1 case in 1 million.

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.

Nutrition disorders and nutritional deficits may cause neurodevelopmental disorders, such as spina bifida, and the rarely occurring anencephaly, both of which are neural tube defects with malformation and dysfunction of the nervous system and its supporting structures, leading to serious physical disability and emotional sequelae. The most common nutritional cause of neural tube defects is folic acid deficiency in the mother, a B vitamin usually found in fruits, vegetables, whole grains, and milk products. (Neural tube defects are also caused by medications and other environmental causes, many of which interfere with folate metabolism, thus they are considered to have multifactorial causes.) Another deficiency, iodine deficiency, produces a spectrum of neurodevelopmental disorders ranging from mild emotional disturbance to severe mental retardation. (see also cretinism)

Excesses in both maternal and infant diets may cause disorders as well, with foods or food supplements proving toxic in large amounts. For instance in 1973 K.L. Jones and D.W. Smith of the University of Washington Medical School in Seattle found a pattern of "craniofacial, limb, and cardiovascular defects associated with prenatal onset growth deficiency and developmental delay" in children of alcoholic mothers, now called fetal alcohol syndrome, It has significant symptom overlap with several other entirely unrelated neurodevelopmental disorders. It has been discovered that iron supplementation in baby formula can be linked to lowered I.Q. and other neurodevelopmental delays.

There is a group called myoclonic dystonia where some cases are hereditary and have been associated with a missense mutation in the dopamine-D2 receptor. Some of these cases have responded well to alcohol.

Other genes that have been associated with dystonia include CIZ1, GNAL, ATP1A3, and PRRT2. Another report has linked THAP1 and SLC20A2 to dystonia.

Developmental coordination disorder (DCD), also known as developmental dyspraxia or simply dyspraxia, is a chronic neurological disorder beginning in childhood. It is also known to affect planning of movements and co-ordination as a result of brain messages not being accurately transmitted to the body. Impairments in skilled motor movements per a child's chronological age which must interfere with activities of daily living. A diagnosis of DCD is then reached only in the absence of other neurological impairments like cerebral palsy, muscular dystrophy, multiple sclerosis or Parkinson's disease. According to CanChild in Canada, this disorder affects 5 to 6 percent of school-aged children; however this disorder does progress towards adulthood, therefore making it a lifelong condition.

Both Thomsen and Becker myotonia have high phenotype variability. Severity of symptoms can vary greatly between individuals and throughout the lives of the individuals themselves. This may be partly because there are over 130 currently known different mutations that can cause the disorder, each with their own specifics, and also because myotonia congenita is an ion channel disorder, and ion channels are sensitive to internal and external environmental factors. It has been shown that pregnancy and the use of diuretics aggravate myotonia, and both these conditions are linked to the loss of divalent cations such as magnesium and calcium. It has further been shown that in pharmacological induced myotonia in isolated rat muscle, myotonia could be dampened by increasing the magnesium and calcium content of the extracellular medium. This has also been shown for isolated human muscle.

Adrenaline/epinephrine is well known to make myotonia worse in most individuals with the disorder, and a person with myotonia congenita may experience a sudden increase in difficulty with mobility in a particularly stressful situation during which adrenaline is released.

Due to the invisible nature of the disorder, the fact that those with myotonia congenita often appear very fit and able bodied, the general lack of knowledge about the disorder by the general and medical community, and often by the individual themselves, and the potential for inconsistency with the symptoms, many people with myotonia congenita have experienced a degree of social persecution at one time or another because of the effects of their disorder.

Currently, research is focusing on identifying the role of the genes on 18p in causing the signs and symptoms associated with deletions of 18p. This will ultimately enable predictive genotyping.

TGIF-Mutations and deletions of this gene have been associated with holoprosencephaly. Penetrance is incomplete, meaning that a deletion of one copy of this gene is not in and of itself sufficient to cause holoprosencephaly. Ten to fifteen percent of people with 18p- have holoprosencephaly, suggesting that other genetic and environmental facts play a role in the etiology of holoprosencephaly in these individuals.

Duane-radial ray syndrome, also known as Okihiro Syndrome, is a rare autosomal dominant disorder that primarily affects the eyes (Duane anomaly) and causes abnormalities of bones in the arms and hands (radial ray malformations). This disorder is considered to be a SALL4-related disorder due to the SALL4 gene mutations leading to these abnormalities. It is diagnosed by clinical findings on a physical exam as well as genetic testing and imaging. After being diagnosed, there are other evaluations that one may go through in order to determine the extent of the disease. There are various treatments for the symptoms of this disorder.

Congenital distal spinal muscular atrophy is caused by a mutation of the "TRPV4" gene found on the 12q23-12q24.1. The mutation causes an affected individual to have lower levels of "TRPV4" expression. This deficiency can lead to abnormal osmotic regulation. Congenital dSMA is genetically heterogeneous, meaning a mutation on this gene can cause a plethora of other phenotypically related or phenotypically unrelated diseases depending on the region that is mutated.

Some conditions known to cause hypotonia include:

Congenital - i.e. disease a person is born with

Duane-radial ray syndrome is caused by mutations in the "SALL4" gene which is a part of a group of genes called the SALL family. This gene plays an important role in embryonic development by providing instructions to make proteins that are involved in the formation of tissues and organs. SALL proteins act as transcription factors in that they attach themselves to certain regions in DNA in order to help control certain gene activities. Due to the mutations in the "SALL4" gene, proteins can not be made because one copy of the gene in each cell is stopped from performing its duty. These mutations are heterozygous and can be nonsense, short duplications, or deletions. At this time, there is no clear reason as to why a reduced amount of the SALL4 protein causes the symptoms of Duane-radial ray syndrome and similar conditions.

Duane-radial ray syndrome is inherited through autosomal dominance meaning that a mutation in one copy of the SALL 4 gene is all it takes to cause this syndrome. Those with this condition can have affected parents, but it can also manifest for the first time with no family history which is called de novo. Since Duane-radial ray syndrome is an autosomal dominant disorder, there is a 50% chance of passing the mutation on to offspring.

A 1998 review noted that life expectancy is usually normal, but that there have occasionally been reported neonatal deaths due to PCD. A 2016 longitudinal study followed 151 adults with PCD for a median of 7 years. Within that span, 7 persons died with a median age of 65.