Athetosis can vary from mild to severe motor dysfunction; it is generally characterized by unbalanced, involuntary movements of muscle and a difficulty maintaining a symmetrical posture. The associated motor dysfunction can be restricted to a part of body or present throughout the body, depending on the individual and the severity of the symptom. One of the pronounced signs can be observed in the extremities in particular, as the writhing, convoluted movement of the digits. Athetosis can appear as early as 18 months from birth with first signs including difficulty feeding, hypotonia, spasm, and involuntary writhing movements of the hands, feet, and face, which progressively worsen through adolescence and at times of emotional distress. Athetosis is caused by lesions in several brain areas such as the hippocampus and the motor thalamus, as well as the corpus striatum; therefore children during the developmental age could possibly suffer from cognitive deficits such as speech impairment, hearing loss, and failed or delayed acquirement of sitting balance.

Athetosis is a symptom characterized by slow, involuntary, convoluted, writhing movements of the fingers, hands, toes, and feet and in some cases, arms, legs, neck and tongue. Movements typical of athetosis are sometimes called "athetoid" movements. Lesions to the brain are most often the direct cause of the symptoms, particularly to the

corpus striatum. This symptom does not occur alone and is often accompanied by the symptoms of cerebral palsy, as it is often a result of this disease. Treatments for athetosis are not very effective, and in most cases are simply aimed at the uncontrollable movement, rather than the cause itself.

Athetosis is defined as a slow, continuous, involuntary writhing movement that prevents the individual from maintaining a stable posture. These are smooth, nonrhythmic movements that appear random and are not composed of any recognizable sub-movements. They mainly involve the distal extremities, but can also involve the face, neck, and trunk. Athetosis can occur in the resting state, as well as in conjunction with chorea and dystonia. When combined with chorea, as in cerebral palsy, the term "choreoathetosis" is frequently used.

Chorea is a continuous, random-appearing sequence of one or more discrete involuntary movements or movement fragments. Although chorea consists of discrete movements, many are often strung together in time, thus making it difficult to identify each movement's start and end point. These movements can involve the face, trunk, neck, tongue, and extremities. Unlike dystonic movements, chorea-associated movements are often more rapid, random and unpredictable. Movements are repeated, but not rhythmic in nature. Children with chorea appear fidgety and will often try to disguise the random movements by voluntarily turning the involuntary, abnormal movement into a seemingly more normal, purposeful motion. Chorea may result specifically from disorders of the basal ganglia, cerebral cortex, thalamus, and cerebellum. It has also been associated with encephalitis, hyperthyroidism, anticholinergic toxicity, and other genetic and metabolic disorders. Chorea is also the prominent movement featured in Huntington's disease.

Chorea is characterized by brief, semi-directed, irregular movements that are not repetitive or rhythmic, but appear to flow from one muscle to the next.

These 'dance-like' movements of chorea often occur with athetosis, which adds twisting and writhing movements. Walking may become difficult, and include odd postures and leg movements.

Unlike ataxia, which affects the quality of voluntary movements, or Parkinsonism, which is a hindrance of voluntary movements, the movements of chorea and ballism occur on their own, without conscious effort. Thus, chorea is said to be a hyperkinetic movement disorder.

When chorea is serious, slight movements will become thrashing motions; this form of severe chorea is referred to as ballism or ballismus.

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.

Chorea (or choreia, occasionally) is an abnormal involuntary movement disorder, one of a group of neurological disorders called dyskinesias. The term "chorea" is derived from the Greek word "χορεία" (=dance; see choreia), as the quick movements of the feet or hands are comparable to dancing.

The term hemichorea refers to chorea of one side of the body, such as chorea of one arm but not both (analogous to hemiballismus).

The attacks consist of dystonia, chorea, and athetosis just like PKD. They are mostly of the limbs, and are usually unilateral or asymmetric. What sets PNKD apart from PKD is that the attacks can last anywhere from four minutes to four hours, but shorter and longer attacks have been reported as well.

The attacks also affect the limbs, usually unilaterally, but bilateral symptoms have also been experienced. PNKD patients usually report the presence of an aura before an attack as well; however they are usually different from those of PKD patients. Once again the aura varies, but is typically felt in the target limb. Another frequently noted aura is dizziness

PNKD patients experience attacks that last much longer than those of PKD. These attacks vary in length and can last anywhere between four minutes and four hours. Similar to the difference between length of attacks, the intervals between attacks are much longer. The Interval between PNKD patients’ attacks is from one day to several months.

PED attacks are characterized in multiple ways. One distinguishing characteristic of PED patients is that they typically experience longer durations of dystonia during their attacks. The most frequent target of attacks are both legs bilaterally, rather than unilateral symptoms. The attacks have also been known to affect the upper half of the body as well. In some cases, patients have had attacks that affected the posturing of their neck and shoulder. Usually there is not an indicative aura symptom prior to a PED attack, which has to do with the nature of the onset of attacks.

The duration and frequency of PED attacks fall between those of PKD and PNKD. The attacks can be relieved with rest, typically taking about 10 minutes from cessation of the exercise. Attacks usually do not last longer than 30 minutes. Attacks typically occur at intervals of between a day and a month, however, there is a great deal of variability here. This variability can be contributed to the nature of the onset of attacks.

Step I : Decide the dominant type of movement disorder

Step II : Make differential diagnosis of the particular disorder

Step II: Confirm the diagnosis by lab tests

- Metabolic screening

- Microbiology

- Immunology

- CSF examination

- Genetics

- Imaging

- Neurophysiological tests

- Pharmacological tests

Choreoathetosis is the occurrence of involuntary movements in a combination of chorea (irregular migrating contractions) and athetosis (twisting and writhing).

It is caused by many different diseases and agents. It is a symptom of several diseases, including Lesch-Nyhan Syndrome, phenylketonuria, and Huntington disease.

Choreoathetosis is also a common presentation of dyskinesia as a side effect of levodopa-carbidopa in the treatment of Parkinson disease.

The condition manifests itself as attacks lasting from a few minutes to several hours. Episodes only happen when the individual is awake, and they remain conscious throughout the attack. Symptoms are most severe in youth and lessen with age. Sufferers can have multiple attacks on a daily basis or may have periods of weeks or months between attacks. Symptoms experienced during attacks can vary and include dystonia, chorea, athetosis, ballismus, or a combination.

Athetoid cerebral palsy or dyskinetic cerebral palsy (sometimes abbreviated ADCP) is primarily associated with damage to the basal ganglia in the form of lesions that occur during brain development due to bilirubin encephalopathy and hypoxic-ischemic brain injury. ADCP is characterized by both hypertonia and hypotonia, due to the affected individual's inability to control muscle tone. Clinical diagnosis of ADCP typically occurs within 18 months of birth and is primarily based upon motor function and neuroimaging techniques.

Athetoid dyskinetic cerebral palsy is a non-spastic, extrapyramidal form of cerebral palsy. Dyskinetic cerebral palsy can be divided into two different groups; choreoathetoid and dystonic. Choreo-athetotic CP is characterized by involuntary movements most predominantly found in the face and extremities. Dystonic ADCP is characterized by slow, strong contractions, which may occur locally or encompass the whole body.

Spastic cerebral palsy, or cerebral palsy where spasticity (muscle tightness) is the exclusive or almost exclusive impairment present, is by far the most common type of overall cerebral palsy, occurring in upwards of 70% of all cases. People with this type of CP are hypertonic and have what is essentially a neuromuscular mobility impairment (rather than hypotonia or paralysis) stemming from an upper motor neuron lesion in the brain as well as the corticospinal tract or the motor cortex. This damage impairs the ability of some nerve receptors in the spine to receive "gamma"-Aminobutyric acid properly, leading to hypertonia in the muscles signaled by those damaged nerves.

As compared to other types of CP, and especially as compared to hypotonic or paralytic mobility disabilities, spastic CP is typically more easily manageable by the person affected, and medical treatment can be pursued on a multitude of orthopedic and neurological fronts throughout life. In any form of spastic CP, clonus of the affected limb(s) may sometimes result, as well as muscle spasms resulting from the pain or stress of the tightness experienced. The spasticity can and usually does lead to a very early onset of muscle stress symptoms like arthritis and tendinitis, especially in ambulatory individuals in their mid-20s and early-30s. Occupational therapy and physical therapy regimens of assisted stretching, strengthening, functional tasks, or targeted physical activity and exercise are usually the chief ways to keep spastic CP well-managed. If the spasticity is too much for the person to handle, other remedies may be considered, such as antispasmodic medications, botulinum toxin, baclofen, or even a neurosurgery known as a selective dorsal rhizotomy (which eliminates the spasticity by reducing the excitatory neural response in the nerves causing it).

While not the same in all people, there are several common triggers that can precipitate an attack:

- Moderate to high consumption of stimulants, such as alcohol, caffeine, or nicotine.

- Low amounts of energy due to hunger, lack of sleep, illness, or physical fatigue.

- Moderate to high presence of stress.

- Menstruation and ovulation.

The characteristic symptom of Costeff syndrome is the onset of progressively worsening eyesight caused by degeneration of the optic nerve (optic atrophy) within the first few years of childhood, with the majority of affected individuals also developing motor disabilities later in childhood. Occasionally, people with Costeff syndrome may also experience mild cognitive disability.

It is type of 3-methylglutaconic aciduria, the hallmark of which is an increased level in the urinary concentrations of 3-methylglutaconic acid and 3-methylglutaric acid; this can allow diagnosis as early as at one year of age.

Those with Costeff syndrome typically experience the first symptoms of visual deterioration within the first few years of childhood, which manifests as the onset of progressively decreasing visual acuity. This decrease tends to continue with age, even after childhood.

The majority of people with Costeff syndrome develop movement problems and motor disabilities later in childhood, the two most significant of which are choreoathetosis and spasticity. The former causes involuntary erratic, jerky, and twisting movements (see chorea and athetosis), whereas the latter causes twitches and spastic tendencies.

These two symptoms are often severe enough to seriously disable an individual; among 36 people with Costeff syndrome, 17 experienced major motor disability as a result of choreoathetosis, and 12 experienced spasticity-related symptoms severe enough to do the same.

Ataxia (loss of muscle coordination) and speech impairment caused by dysarthria also occur in roughly 50% of cases, but are rarely seriously disabling.

Some individuals with Costeff disease also display mild cognitive impairment, though such cases are relatively infrequent.

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.

Damage to the corpus callosum can give rise to "purposeful" actions in the sufferer's non-dominant hand (an individual who is left-hemisphere-dominant will experience the left hand becoming alien, and the right hand will turn alien in the person with right-hemisphere dominance).

In "the callosal variant", the patient's hand counteracts voluntary actions performed by the other, "good" hand. Two phenomena that are often found in patients with callosal alien hand are "agonistic dyspraxia" and "diagonistic dyspraxia".

Agonistic dyspraxia involves compulsive automatic execution of motor commands by one hand when the patient is asked to perform movements with the other hand. For example, when a patient with callosal damage was instructed to pull a chair forward, the affected hand would decisively and impulsively push the chair backwards.

Agonistic dyspraxia can thus be viewed as an involuntary competitive interaction between the two hands directed toward completion of a desired act in which the affected hand competes with the unaffected hand to complete a purposive act originally intended to be performed by the unaffected hand.

Diagonistic dyspraxia, on the other hand, involves a conflict between the desired act in which the unaffected hand has been engaged and the interfering action of the affected hand which works to oppose the purpose of the desired act intended to be performed by the unaffected hand. For instance, when Akelaitis's patients underwent surgery to the corpus callosum to reduce epileptic seizures, one patient's left alien hand would frequently interfere with the right hand. For instance, while trying to turn over to the next page with the right hand, his left hand would try to close the book.

In another case of callosal alien hand, the patient did not suffer from intermanual conflict between the hands but rather from a symptom characterized by involuntary mirror movements of the affected hand. When the patient was asked to perform movements with one hand, the other hand would involuntarily perform a mirror image movement which continued even when the involuntary movement was brought to the attention of the patient, and the patient was asked to restrain the mirrored movement. The patient suffered from a ruptured aneurysm near the anterior cerebral artery, which resulted in the right hand being mirrored by the left hand. The patient described the left hand as frequently interfering and taking over anything the patient tried to do with the right hand. For instance, when trying to grasp a glass of water with the right hand with a right side approach, the left hand would involuntary reach out and grasp hold of the glass through a left side approach.

More recently, Geschwind et al. described the case of a woman who suffered severe coronary heart disease. One week after undergoing coronary artery bypass grafting, she noticed that her left hand started to "live a life of its own". It would unbutton her gown, try to choke her while asleep and would automatically fight with the right hand to answer the phone. She had to physically restrain the affected hand with the right hand to prevent injury, a behavior which has been termed "self-restriction". The left hand also showed signs of severe ideomotor apraxia. It was able to mimic actions but only with the help of mirror movements executed by the right hand (enabling synkinesis). Using magnetic resonance imaging (MRI), Geschwind et al. found damage to the posterior half of the callosal body, sparing the anterior half and the splenium extending slightly into the white matter underlying the right cingulate cortex.

"Alien behavior" can be distinguished from reflexive behavior in that the former is flexibly purposive while the latter is obligatory. Sometimes the sufferer will not be aware of what the alien hand is doing until it is brought to his or her attention, or until the hand does something that draws their attention to its behavior. There is a clear distinction between the behaviors of the two hands in which the affected hand is viewed as "wayward" and sometimes "disobedient" and generally out of the realm of their own voluntary control, while the unaffected hand is under normal volitional control. At times, particularly in patients who have sustained damage to the corpus callosum that connects the two cerebral hemispheres (see also split-brain), the hands appear to be acting in opposition to each other.

A related syndrome described by the French neurologist François Lhermitte involves the release through disinhibition of a tendency to compulsively utilize objects that present themselves in the surrounding environment around the patient. The behavior of the patient is, in a sense, obligatorily linked to the "affordances" (using terminology introduced by the American ecological psychologist, James J. Gibson) presented by objects that are located within the immediate peri-personal environment.

This condition, termed "utilization behavior", is most often associated with extensive bilateral frontal lobe damage and might actually be thought of as "bilateral" alien hand syndrome in which the patient is compulsively directed by external environmental contingencies (e.g. the presence of a hairbrush on the table in front of them elicits the act of brushing the hair) and has no capacity to "hold back" and inhibit pre-potent motor programs that are obligatorily linked to the presence of specific external objects in the peri-personal space of the patient. When the frontal lobe damage is bilateral and generally more extensive, the patient completely loses the ability to act in a self-directed manner and becomes totally dependent upon the surrounding environmental indicators to guide his behavior in a general social context, a condition referred to as "environmental dependency syndrome".

In order to deal with the alien hand, some patients engage in personification of the affected hand. Usually these names are negative in nature, from mild such as "cheeky" to malicious "monster from the moon". For example, Doody and Jankovic described a patient who named her alien hand "baby Joseph". When the hand engaged in playful, troublesome activities such as pinching her nipples (akin to biting while nursing), she would experience amusement and would instruct baby Joseph to "stop being naughty". Furthermore, Bogen suggested that certain personality characteristics, such as a flamboyant personality, contribute to frequent personification of the affected hand.

Neuroimaging and pathological research shows that the frontal lobe (in the frontal variant) and corpus callosum (in the callosal variant) are the most common anatomical lesions responsible for the alien hand syndrome. These areas are closely linked in terms of motor planning and its final pathways.

The callosal variant includes advanced willed motor acts by the non-dominant hand, where patients frequently exhibit "intermanual conflict" in which one hand acts at cross-purposes with the other "good hand". For example, one patient was observed putting a cigarette into her mouth with her intact, "controlled" hand (her right, dominant hand), following which her alien, non-dominant, left hand came up to grasp the cigarette, pull the cigarette out of her mouth, and toss it away before it could be lit by the controlled, dominant, right hand. The patient then surmised that "I guess 'he' doesn't want me to smoke that cigarette." Another patient was observed to be buttoning up her blouse with her controlled dominant hand while the alien non-dominant hand, at the same time, was unbuttoning her blouse. The frontal variant most often affects the dominant hand, but can affect either hand depending on the lateralization of the damage to medial frontal cortex, and includes grasp reflex, impulsive groping toward objects or/and tonic grasping (i.e. difficulty in releasing grip).

In most cases, classic alien-hand signs derive from damage to the medial frontal cortex, accompanying damage to the corpus callosum. In these patients the main cause of damage is unilateral or bilateral infarction of cortex in the territory supplied by the anterior cerebral artery or associated arteries. Oxygenated blood is supplied by the anterior cerebral artery to most medial portions of the frontal lobes and to the anterior two-thirds of the corpus callosum, and infarction may consequently result in damage to multiple adjacent locations in the brain in the supplied territory. As the medial frontal lobe damage is often linked to lesions of the corpus callosum, frontal variant cases may also present with callosal form signs. Cases of damage restricted to the callosum however, tend not to show frontal alien-hand signs.

There is substantial variability in the severity of features of A-T among affected individuals, and at different ages. The following symptoms or problems are either common or important features of A-T:

- Ataxia (difficulty with control of movement) that is apparent early but worsens in school to pre-teen years

- Oculomotor apraxia (difficulty with coordination of head and eye movement when shifting gaze from one place to the next)

- Involuntary movements

- Telangiectasia (dilated blood vessels) over the white (sclera) of the eyes, making them appear bloodshot. These are not apparent in infancy and may first appear at age 5–8 years. Telangiectasia may also appear on sun-exposed areas of skin.

- Problems with infections, especially of the ears, sinuses and lungs

- Increased incidence of cancer (primarily, but not exclusively, lymphomas and leukemias)

- Delayed onset or incomplete pubertal development, and very early menopause

- Slowed rate of growth (weight and/or height)

- Drooling particularly in young children when they are tired or concentrating on activities

- Dysarthria (slurred, slow, or distorted speech sounds)

- Diabetes in adolescence or later

- Premature changes in hair and skin

Many children are initially misdiagnosed as having ataxic cerebral palsy. The diagnosis of A-T may not be made until the preschool years when the neurologic symptoms of impaired gait, hand coordination, speech and eye movement appear or worsen, and the telangiectasia first appear. Because A-T is so rare, doctors may not be familiar with the symptoms, or methods of making a diagnosis. The late appearance of telangiectasia may be a barrier to the diagnosis. It may take some time before doctors consider A-T as a possibility because of the early stability of symptoms and signs.

The first indications of A-T usually occur during the toddler years. Children start walking at a normal age, but may not improve much from their initial wobbly gait. Sometimes they have problems standing or sitting still and tend to sway backward or from side to side. In primary school years, walking becomes more difficult, and children will use doorways and walls for support. Children with A-T often appear better when running or walking quickly in comparison to when they are walking slowly or standing in one place. Around the beginning of their second decade, children with typical forms of A-T start using a wheelchair for long distances. During school years, children may have increasing difficulty with reading because of impaired coordination of eye movement. At the same time, other problems with fine-motor functions (writing, coloring, and using utensils to eat), and with slurring of speech (dysarthria) may arise. Most of these neurologic problems stop progressing after the age of about 12 – 15 years, though involuntary movements may start at any age and may worsen over time. These extra movements can take many forms, including small jerks of the hands and feet that look like fidgeting (chorea), slower twisting movements of the upper body (athetosis), adoption of stiff and twisted postures (dystonia), occasional uncontrolled jerks (myoclonic jerks), and various rhythmic and non-rhythmic movements with attempts at coordinated action (tremors).

All forms of MDDS are very rare. MDDS causes a wide range of symptoms, which can appear in newborns, infants, children, or adults, depending on the class of MDDS; within each class symptoms are also diverse.

In MDDS associated with mutations in "TK2", infants generally develop normally, but by around two years of age, symptoms of general muscle weakness (called "hypotonia"), tiredness, lack of stamina, and difficulty feeding begin to appear. Some toddlers start to lose control of the muscles in their face, mouth, and throat, and may have difficulty swallowing. Motor skills that had been learned may be lost, but generally the functioning of the brain and ability to think are not affected.

In MDDS associated with mutations in "SUCLA2" or "SUCLG1" that primarily affect the brain and muscle, hypotonia generally arises in infants before they are 6 months old, their muscles begin wasting away, and there is delay in psychomotor learning (learning basic skills like walking, talking, and intentional, coordinated movement). The spine often begins to curve (scoliosis or kyphosis), and the child often has abnormal movements (dystonia, athetosis or chorea), difficulty feeding, acid reflux, hearing loss, stunted growth, and difficulty breathing that can lead to frequent lung infections. Sometime epilepsy develops.

In MDDS associated with mutations in "RRM2B" that primarily affect the brain and muscle, there is again hypotonia in the first months, symptoms of lactic acidosis like nausea, vomiting, and rapid deep breathing, failure to thrive including the head remaining small, delay or regression in moving, and hearing loss. Many body systems are affected.

In MDDS associated with mutations in "DGUOK" that primarily affect the brain and the liver, there are two forms. There is an early-onset form in which symptoms arise from problems in many organs in the first week of life, especially symptoms of lactic acidosis as well as low blood sugar. Within weeks of birth they can develop liver failure and the associated jaundice and abdominal swelling, and many neurological problems including developmental delays and regression, and uncontrolled eye movement. Rarely within class of already rare diseases, symptoms only relating to liver disease emerge later in infancy or in childhood.

In MDDS associated with mutations in "MPV17" that primarily affect the brain and the liver, the symptoms are similar to those caused by DGUOK and also emerge shortly after birth, generally with fewer and less severe neurological problems. There is a subset of people of Navajo descent who develop Navajo neurohepatopathy, who in addition to these symptoms also have easily broken bones that do not cause pain, deformed hands or feet, and problems with their corneas.

In MDDS associated with mutations in "POLG" that primarily affect the brain and the liver, the symptoms are very diverse and can emerge anytime from shortly after birth to old age. The first signs of the disease, which include intractable seizures and failure to meet meaningful developmental milestones, usually occur in infancy, after the first year of life, but sometimes as late as the fifth year. Primary symptoms of the disease are developmental delay, progressive intellectual disability, hypotonia (low muscle tone), spasticity (stiffness of the limbs) possibly leading to quadriplegia, and progressive dementia. Seizures may include epilepsia partialis continua, a type of seizure that consists of repeated myoclonic (muscle) jerks. Optic atrophy may also occur, often leading to blindness. Hearing loss may also occur. Additionally, although physical signs of chronic liver dysfunction may not be present, many people suffer liver impairment leading to liver failure.

In MDDS associated with mutations in "PEO1"/"C10orf2" that primarily affect the brain and the liver, symptoms emerge shortly after birth or in early infancy, with hypotonia, symptoms of lactic acidosis, enlarged liver, feeding problems, lack of growth, and delay of psychomotor skills. Neurologically, development is slowed or stopped, and epilepsy emerges, as do sensory problems like loss of eye control and deafness, and neuromuscular problems like a lack of reflexes, muscular atrophy, and twitching, and epilepsy.

In MDDS associated with mutations in the genes associated with mutations in "ECGF1"/"TYMP" that primarily affects the brain and the gastrointestinal tract, symptoms can emerge any time in the first fifty years of life; most often they emerge before the person turns 20. Weight loss is common as is a lack of the ability of the stomach and intestines to automatically expand and contract and thus move through it (called gastrointestinal motility) – this leads to feeling full after eating only small amounts of food, nausea, acid reflux, All affected individuals develop weight loss and progressive gastrointestinal dysmotility manifesting as early satiety, nausea, diarrhea, vomiting, and stomach pain and swelling. People also develop neuropathy, with weakness and tingling. There are often eye problems, and intellectual disability.

6-Pyruvoyltetrahydropterin synthase deficiency is an autosomal recessive disorder that causes malignant hyperphenylalaninemia due to tetrahydrobiopterin deficiency.

It belongs to the rare diseases. It is a recessive disorder that is accompanied by hyperphenylalaninemia. Commonly reported symptoms are initial truncal hypotonia, subsequent appendicular hypertonia, bradykinesia, cogwheel rigidity, generalized dystonia, and marked diurnal fluctuation. Other reported clinical features include difficulty in swallowing, oculogyric crises, somnolence, irritability, hyperthermia, and seizures. Chorea, athetosis, hypersalivation, rash with eczema, and sudden death have also been reported. Patients with mild phenotypes may deteriorate if given folate antagonists such as methotrexate, which can interfere with a salvage pathway through which dihydrobiopterin is converted into tetrahydrobiopterin via dihydrofolate reductase. Treatment options include substitution with neurotransmitter precursors (levodopa, 5-hydroxytryptophan), monoamine oxidase inhibitors, and tetrahydrobiopterin. Response to treatment is variable and the long-term and functional outcome is unknown. To provide a basis for improving the understanding of the epidemiology, genotype/phenotype correlation and outcome of these diseases their impact on the quality of life of patients, and for evaluating diagnostic and therapeutic strategies a patient registry was established by the noncommercial International Working Group on Neurotransmitter Related Disorders (iNTD).

Mitochondrial DNA depletion syndrome (MDS or MDDS) is any of a group of autosomal recessive disorders that cause a significant drop in mitochondrial DNA in affected tissues. Symptoms can be any combination of myopathic, hepatopathic, or encephalomyopathic. These syndromes affect tissue in the muscle, liver, or both the muscle and brain, respectively. The condition is typically fatal in infancy and early childhood, though some have survived to their teenage years with the myopathic variant and some have survived into adulthood with the SUCLA2 encephalomyopathic variant. There is currently no curative treatment for any form of MDDS, though some preliminary treatments have shown a reduction in symptoms.