The most common first sign of MSA is the appearance of an "akinetic-rigid syndrome" (i.e. slowness of initiation of movement resembling Parkinson's disease) found in 62% at first presentation. Other common signs at onset include problems with balance (cerebellar ataxia) found in 22% at first presentation, followed by genito-urinary problems (9%). For men, the first sign can be erectile dysfunction (inability to achieve or sustain an erection). Women have also reported reduced genital sensitivity. Both men and women often experience problems with their bladders including urgency, frequency, incomplete bladder emptying, or an inability to pass urine (retention). About 1 in 5 MSA patients will fall in their first year of disease.

In contrast to amyotrophic lateral sclerosis or primary lateral sclerosis, PMA is distinguished by the "absence" of:

- brisk reflexes

- spasticity

- Babinski's sign

- Emotional lability

MSA is characterized by a combination of the following, which can be present in any combination:

- autonomic dysfunction

- parkinsonism (muscle rigidity +/ tremor and slow movement)

- ataxia (Poor coordination / unsteady walking)

A variant with combined features of MSA and Lewy body dementia may also exist. There have also been occasional instances of frontotemporal lobar degeneration associated with MSA.

As a result of lower motor neurone degeneration, the symptoms of PMA include:

- atrophy

- fasciculations

- muscle weakness

Some patients have symptoms restricted only to the arms or legs (or in some cases just one of either). These cases are referred to as "Flail Arm" (FA) or "Flail Leg" (FL) and are associated with a better prognosis.

Spinocerebellar ataxia (SCA) is one of a group of genetic disorders characterized by slowly progressive incoordination of gait and is often associated with poor coordination of hands, speech, and eye movements. A review of different clinical features among SCA subtypes was recently published describing the frequency of non-cerebellar features, like parkinsonism, chorea, pyramidalism, cognitive impairment, peripheral neuropathy, seizures, among others. As with other forms of ataxia, SCA frequently results in atrophy of the cerebellum, loss of fine coordination of muscle movements leading to unsteady and clumsy motion, and other symptoms.

The symptoms of an ataxia vary with the specific type and with the individual patient. In general, a person with ataxia retains full mental capacity but progressively loses physical control.

Individuals with SBMA have muscle cramps and progressive weakness due to degeneration of motor neurons in the brain stem and spinal cord. Ages of onset and severity of manifestations in affected males vary from adolescence to old age, but most commonly develop in middle adult life. The syndrome has neuromuscular and endocrine manifestations.

Early signs often include weakness of tongue and mouth muscles, fasciculations, and gradually increasing weakness of limb muscles with muscle wasting. Neuromuscular management is supportive, and the disease progresses very slowly, but can eventually lead to extreme disability. Further signs and symptoms include:

Symptoms typically begin sometime between the ages of 5 to 15 years, but in Late Onset FA may occur in the 20s or 30s. Symptoms include any combination, but not necessarily all, of the following:

- Muscle weakness in the arms and legs

- Loss of coordination

- Vision impairment

- Hearing impairment

- Slurred speech

- Curvature of the spine (scoliosis)

- High plantar arches (pes cavus deformity of the foot)

- Diabetes (about 20% of people with Friedreich's ataxia develop carbohydrate intolerance and 10% develop diabetes mellitus)

- Heart disorders (e.g., atrial fibrillation, and resultant tachycardia (fast heart rate) and hypertrophic cardiomyopathy)

It presents before 22 years of age with progressive staggering or stumbling gait and frequent falling. Lower extremities are more severely involved. The symptoms are slow and progressive. Long-term observation shows that many patients reach a plateau in symptoms in the patient's early adulthood. On average, after 10–15 years with the disease, patients are usually wheelchair bound and require assistance with all activities of daily living.

The following physical signs may be detected on physical examination:

- Cerebellar: nystagmus, fast saccadic eye movements, truncal ataxia, dysarthria, dysmetria.

- Lower motor neuron lesion: absent deep tendon reflexes.

- Pyramidal: extensor plantar responses, and distal weakness are commonly found.

- Dorsal column: Loss of vibratory and proprioceptive sensation occurs.

- Cardiac involvement occurs in 91% of patients, including cardiomegaly (up to dilated cardiomyopathy), symmetrical hypertrophy, heart murmurs, and conduction defects. Median age of death is 35 years, while females have better prognosis with a 20-year survival of 100% as compared to 63% in men.

20% of cases are found in association with diabetes mellitus.

OPCA is characterized by progressive cerebellar ataxia, leading to clumsiness in body movements, veering from midline when walking, wide-based stance, and falls without signs of paralysis or weakness. Clinical presentation can vary greatly between patients, but mostly affects speech, balance and walking. Other possible neurological problems include spasmodic dysphonia, hypertonia, hyperreflexia, rigidity, dysarthria, dysphagia and neck dystonic posture.

Spinocerebellar ataxia (SCA), also known as spinocerebellar atrophy or spinocerebellar degeneration, is a progressive, degenerative, genetic disease with multiple types, each of which could be considered a disease in its own right. An estimated 150,000 people in the United States have a diagnosis of spinocerebellar ataxia at any given time. SCA is hereditary, progressive, degenerative, and often fatal. There is no known effective treatment or cure. SCA can affect anyone of any age. The disease is caused by either a recessive or dominant gene. In many cases people are not aware that they carry a relevant gene until they have children who begin to show signs of having the disorder.

The symptoms vary depending on the SMA type, the stage of the disease as well as individual factors. Signs and symptoms below are most common in the severe SMA type 0/I:

- Areflexia, particularly in extremities

- Overall muscle weakness, poor muscle tone, limpness or a tendency to flop

- Difficulty achieving developmental milestones, difficulty sitting/standing/walking

- In small children: adopting of a frog-leg position when sitting (hips abducted and knees flexed)

- Loss of strength of the respiratory muscles: weak cough, weak cry (infants), accumulation of secretions in the lungs or throat, respiratory distress

- Bell-shaped torso (caused by using only abdominal muscles for respiration) in severe SMA type

- Fasciculations (twitching) of the tongue

- Difficulty sucking or swallowing, poor feeding

The disorder causes muscle weakness and atrophy throughout the body due to the degeneration of the upper and lower motor neurons. Individuals affected by the disorder may ultimately lose the ability to initiate and control all voluntary movement, although bladder and bowel function and the muscles responsible for eye movement are usually spared until the final stages of the disorder.

Cognitive or behavioral dysfunction is present in 30–50% of individuals with ALS. Around half of people with ALS will experience mild changes in cognition and behavior, and 10–15% will show signs of frontotemporal dementia. Repeating phrases or gestures, apathy, and loss of inhibition are frequently reported behavioral features of ALS. Language dysfunction, executive dysfunction, and troubles with social cognition and verbal memory are the most commonly reported cognitive symptoms in ALS; a meta-analysis found no relationship between dysfunction and disease severity. However, cognitive and behavioral dysfunctions have been found to correlate with reduced survival in people with ALS and increased caregiver burden; this may be due in part to deficits in social cognition. About half the people who have ALS experience emotional lability, in which they cry or laugh for no reason.

Sensory nerves and the autonomic nervous system are generally unaffected, meaning the majority of people with ALS maintain hearing, sight, touch, smell, and taste.

The start of ALS may be so subtle that the symptoms are overlooked. The earliest symptoms of ALS are muscle weakness or muscle atrophy. Other presenting symptoms include trouble swallowing or breathing, cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; or slurred and nasal speech. The parts of the body affected by early symptoms of ALS depend on which motor neurons in the body are damaged first.

In limb-onset ALS, people first experience awkwardness when walking or running or even tripping over or stumbling may be experienced and often this is marked by walking with a "dropped foot" which drags gently on the ground. Or if arm-onset, difficulty with tasks requiring manual dexterity such as buttoning a shirt, writing, or turning a key in a lock may be experienced.

In bulbar-onset ALS, initial symptoms will mainly be of difficulty speaking clearly or swallowing. Speech may become slurred, nasal in character, or quieter. There may be difficulty in swallowing and loss of tongue mobility. A smaller proportion of people experience "respiratory-onset" ALS, where the intercostal muscles that support breathing are affected first.

Over time, people experience increasing difficulty moving, swallowing (dysphagia), and speaking or forming words (dysarthria). Symptoms of upper motor neuron involvement include tight and stiff muscles (spasticity) and exaggerated reflexes (hyperreflexia) including an overactive gag reflex. An abnormal reflex commonly called Babinski's sign also indicates upper motor neuron damage. Symptoms of lower motor neuron degeneration include muscle weakness and atrophy, muscle cramps, and fleeting twitches of muscles that can be seen under the skin (fasciculations) although twitching is not a diagnostic symptom and more of a side effect so twitching would either occur after or accompany weakness and atrophy.

Neuropathy disorders usually have onset in childhood or young adulthood. Motor symptoms seem to be more predominant that sensory symptoms. Symptoms of these disorders include: fatigue, pain, lack of balance, lack of feeling, lack of reflexes, and lack of sight and hearing, which result from muscle atrophy. Patients can also suffer from high arched feet, hammer toes, foot drop, foot deformities, and scoliosis. These symptoms are a result of severe muscular weakness and atrophy. In patients suffering from demyelinating neuropathy, symptoms are due to slow nerve conduction velocities, however people with axonal degradation have average to normal nerve conduction velocities.

Olivopontocerebellar atrophy (OPCA) is the degeneration of neurons in specific areas of the brain – the cerebellum, pons, and inferior olives. OPCA is present in several neurodegenerative syndromes, including inherited and non-inherited forms of ataxia (such as the hereditary spinocerebellar ataxia known as Machado–Joseph disease) and multiple system atrophy (MSA), with which it is primarily associated.

OPCA may also be found in the brains of individuals with prion disorders and inherited metabolic diseases. The characteristic areas of brain damage that indicate OPCA can be seen by imaging the brain using CT scans or MRI studies.

The term was originally coined by Joseph Jules Dejerine and André Thomas.

Onset usually occurs within the first two decades of life, commonly in the teenage years or the twenties. Life expectancy is normal. High arch of the foot (pes cavus) is common. Patients also have trouble controlling their hands, due to muscle loss on the thumb side of the index finger and palm below the thumb. It is rare for a person with this disorder to lose the ability to walk, though changes in gait may occur later in life.

Frequency of this disorder is unknown.

In an individual with dHMN V, electromyography will show pure motor neuropathy, patterns of weakness without upper motor neuron damage, in the hands. Tendon reflexes will also appear normal. Clinical, electrophysiological, and pathological testing will show a lack of damage to sensory neurons, differentiating this disease from CMT.

Friedreich's ataxia is an autosomal recessive inherited disease that causes progressive damage to the nervous system. It manifests in initial symptoms of poor coordination such as gait disturbance; it can also lead to scoliosis, heart disease and diabetes, but does not affect cognitive function. The disease is progressive, and ultimately a wheelchair is required for mobility. Its incidence in the general population is roughly 1 in 50,000.

The particular genetic mutation (expansion of an intronic GAA triplet repeat in the FXN gene) leads to reduced expression of the mitochondrial protein frataxin. Over time this deficiency causes the aforementioned damage, as well as frequent fatigue due to effects on cellular metabolism.

The ataxia of Friedreich's ataxia results from the degeneration of nervous tissue in the spinal cord, in particular sensory neurons essential (through connections with the cerebellum) for directing muscle movement of the arms and legs. The spinal cord becomes thinner and nerve cells lose some of their myelin sheath (the insulating covering on some nerve cells that helps conduct nerve impulses).

The condition is named after the German physician Nikolaus Friedreich, who first described it in the 1860s.

SMA manifests over a wide range of severity, affecting infants through adults. The disease spectrum is variously divided into 3–5 types, in accordance either with the age of onset of symptoms or with the highest attained milestone of motor development.

The most commonly used classification is as follows:

The most severe form of SMA type I is sometimes termed SMA type 0 (or, severe infantile SMA) and is diagnosed in babies that are born so weak that they can survive only a few weeks even with intensive respiratory support. SMA type 0 should not be confused with SMARD1 which may have very similar symptoms and course but has a different genetic cause than SMA.

Motor development in people with SMA is usually assessed using validated functional scales – CHOP INTEND (The Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders) in SMA1; and either the Motor Function Measure scale or one of a few variants of Hammersmith Functional Motor Scale in SMA types 2 and 3.

The eponymous label "Werdnig–Hoffmann disease" (sometimes misspelled with a single "n") refers to the earliest clinical descriptions of childhood SMA by Johann Hoffmann and Guido Werdnig. The eponymous term "Kugelberg–Welander disease" is after Erik Klas Hendrik Kugelberg (1913-1983) and Lisa Welander (1909-2001), who distinguished SMA from muscular dystrophy. Rarely used "Dubowitz disease" (not to be confused with Dubowitz syndrome) is named after Victor Dubowitz, an English neurologist who authored several studies on the intermediate SMA phenotype.

BVVL is marked by a number of cranial nerve palsies, including those of the motor components involving the 7th and 9th-12th cranial nerves, spinal motor nerves, and upper motor neurons. Major features of BVVL include facial and neck weakness, fasciculation of the tongue, and neurological disorders from the cranial nerves. The neurological manifestations develop insidiously: they usually begin with sensorineural deafness, progress inexorably to paralysis, and often culminate in respiratory failure. Most mortality in patients has been from either respiratory infections or respiratory muscle paralysis. Pathological descriptions of BVVL include injury and depletion of 3rd-7th cranial nerves, loss of the spinal anterior horn cells, degeneration of Purkinje cells, as well as degeneration of the spinocerebellar and pyramidal tracts. The first symptoms in nearly all cases of BVVL is progressive vision loss and deafness, and the first initial symptoms are seen anywhere from one to three years.

Most cases of deafness are followed by a latent period that can extend anywhere from weeks to years, and this time is usually marked by cranial nerve degeneration. Neurological symptoms of BVVL include optic atrophy, cerebellar ataxia, retinitis pigmentosa, epilepsy and autonomic dysfunction. Non-neurological symptoms can include diabetes, auditory hallucinations, respiratory difficulties, color blindness, and hypertension.

Based on the type of muscles affected, spinal muscular atrophies can be divided into:

- "Proximal spinal muscular atrophies", i.e., conditions that affect primarily proximal muscles;

- "Distal spinal muscular atrophies" (which significantly overlap with distal hereditary motor neuronopathies) where they affect primarily distal muscles.

When taking into account prevalence, spinal muscular atrophies are traditionally divided into:

- "Autosomal recessive proximal spinal muscular atrophy", responsible for 90-95% of cases and usually called simply "spinal muscular atrophy" (SMA) – a disorder associated with a genetic mutation on the "SMN1" gene on chromosome 5q (locus 5q13), affecting people of any age but in its most severe form being the most common genetic cause of infant death;

- "Localised spinal muscular atrophies" – much more rare conditions, in some instances described in but a few patients in the world, which are associated with mutations of genes other than "SMN1" and for this reason sometimes termed simply "non-5q spinal muscular atrophies".

A more detailed classification is based on the gene associated with the condition (where identified) and is presented in table below.

In all forms of SMA (with an exception of X-linked spinal muscular atrophy type 1), only motor neurons, located at the anterior horn of spinal cord, are affected; sensory neurons, which are located at the posterior horn of spinal cord, are not affected. By contrast, hereditary disorders that cause both weakness due to motor denervation along with "sensory" impairment due to sensory denervation are known as hereditary motor and sensory neuropathies (HMSN).

In all spinal muscular atrophies, the primary feature is muscle weakness accompanied by atrophy of muscle. This is the result of denervation, or loss of the signal to contract that is transmitted by the motor neurons in the spinal cord. The signal is normally transmitted from the spinal cord to muscle via the motor neuron's axon, but in spinal muscular atrophies either the entire motor neuron or the motor neuron's axon loses the ability to transmit signals to muscles.

The symptoms are strongly related to the exact disease (see above) and, sometimes, to the age of onset. Certain conditions (e.g., spinal muscular atrophy or spinal and bulbar muscular atrophy) have a wide range, from infancy to adult, fatal to trivial, with different affected individuals manifesting every shade of impairment between these two extremes. Other muscular atrophies have a different and often very severe course. Some of them are extremely rare and described only in a handful of individuals. However, in all cases the majority of symptoms are a consequence of muscle weakness.

Prognosis for PBP patients is poor. Progressive bulbar palsy symptoms can include progressive difficulty with chewing, talking, and swallowing. Patients can also exhibit reduced gag reflexes, weak palatal movements, fasciculations, and weak movement of the facial muscles and tongue. In advanced cases of PBP, the patient may be unable to protrude their tongue or manipulate food in their mouth.

Patients with early cases of PBP have difficulty with pronunciations, particularly lateral consonants (linguals) and velars, and may show problems with drooling saliva. If the corticobulbar tract is affected a pseudobulbar affect with emotional changes may occur. Because PBP patients have such difficulty swallowing, food and saliva can be inhaled into the lungs. This can cause gagging and choking, and it increases the risk of pneumonia. Death, which is often from pneumonia, usually occurs 1 to 3 years after the start of the disorder.

Onset : Early childhood

Progression: Chronic progressive

Clinical: Cerebellar ataxia plus syndrome / Optic Atrophy Plus Syndrome

Ocular: Optic atrophy, nystagmus, scotoma, and bilateral retrobulbar neuritis.

Other: Mental retardation, myoclonic epilepsy, spasticity, and posterior column sensory loss. Tremor in some cases.

Musculoskeletal

Contractures, lower limbs, Achilles tendon contractures, Hamstring contractures, Adductor longus contractures

Systemic

Hypogonadotrophic hypogonadism.

X-linked spinal muscular atrophy type 2 (SMAX2, XLSMA), also known as arthrogryposis multiplex congenita X-linked type 1 (AMCX1), is a rare neurological disorder involving death of motor neurons in the anterior horn of spinal cord resulting in generalised muscle wasting (atrophy). The disease is caused by a mutation in "UBA1" gene and is passed in a X-linked recessive manner by carrier mothers to affected sons.

Affected babies have general muscle weakness, weak cry and floppy limbs; consequently, the condition is usually apparent at or even before birth. Symptoms resemble the more severe forms of the more common spinal muscular atrophy (SMA); however, SMAX2 is caused by a different genetic defect and only genetic testing can correctly identify the disease.

The disorder is usually fatal in infancy or early childhood due to progressive respiratory failure, although survival into teenage years have been reported. As with many genetic disorders, there is no known cure to SMAX2. Appropriate palliative care may be able to increase quality of life and extend lifespan.