Symptoms depend on the type of HSP inherited. The main feature of the disease is progressive spasticity in the lower limbs due to pyramidal tract dysfunction. This also results in brisk reflexes, extensor plantar reflexes, muscle weakness, and variable bladder disturbances. Furthermore, among the core symptoms of HSP are also included abnormal gait and difficulty in walking, decreased vibratory sense at the ankles, and paresthesia.

Initial symptoms are typically difficulty with balance, stubbing the toe or stumbling. Symptoms of HSP may begin at any age, from infancy to older than 60 years. If symptoms begin during the teenage years or later, then spastic gait disturbance usually progresses over many years. Canes, walkers, and wheelchairs may eventually be required, although some people never require assistance devices.

More specifically, patients with the autosomal dominant pure form of HSP reveal normal facial and extraocular movement. Although jaw jerk may be brisk in older subjects, there is no speech disturbance or difficulty of swallowing. Upper extremity muscle tone and strength are normal. In the lower extremities, muscle tone is increased at the hamstrings, quadriceps and ankles. Weakness is most notable at the iliopsoas, tibialis anterior, and to a lesser extent, hamstring muscles.

In the complex form of the disorder, additional symptoms are present. These include: peripheral neuropathy, amyotrophy, ataxia, mental retardation, ichthyosis, epilepsy, optic neuropathy, dementia, deafness, or problems with speech, swallowing or breathing.

Anita Harding classified the HSP in a pure and complicated form. Pure HSP presents with spasticity in the lower limbs, associated with neurogenic bladder disturbance as well as lack of vibration sensitivity (pallhypesthesia). On the other hand, HSP is classified as complex when lower limb spasticity is combined with any additional neurological symptom.

This classification is subjective and patients with complex HSPs are sometimes diagnosed as having cerebellar ataxia with spasticity, mental retardation (with spasticity), or leukodystrophy. Some of the genes listed below have been described in other diseases than HSP before. Therefore, some key genes overlap with other disease groups.

ARSACS is usually diagnosed in early childhood, approximately 12–24 months of age when a child begins to take their first steps. At this time it manifests as a lack of coordination and balance resulting in frequent falls. Some of the signs and symptoms include:

- Stiffness of the legs

- Appendicular and trunk ataxia

- Hollow foot and hand deformities

- Ataxic dysarthria

- Distal muscle wasting

- Horizontal gaze nystagmus

- Spasticity

In the past, HSP has been classified as early onset beginning in early childhood or later onset in adulthood. The age of onsets has two points of maximum at age 2 and around age 40. New findings propose that an earlier onset leads to a longer disease duration without loss of ambulation or the need for the use of a wheelchair. This was also described earlier, that later onset forms evolve more rapidly.

Autosomal Recessive Spastic Ataxia of the Charlevoix-Saguenay (ARSACS) is a very rare neurodegenerative genetic disorder that primarily affects people from the Saguenay–Lac-Saint-Jean and Charlevoix regions of Quebec or descendants of native settlers in this region. This disorder has also been demonstrated in people from various other countries including India, Turkey, Japan, The Netherlands, Italy, Belgium, France and Spain. The prevalence has been estimated at about 1 in 1900 in Quebec, but it is very rare elsewhere.

At the beginning, affected individuals often notice the loss of pain and temperature sensation or all sensory modalities in their feet. As the disease progresses, the sensory abnormalities may extend up to the knees. However, they often do not notice sensory loss for a long time. Many affected individuals only become aware of the disease when they notice painless injuries and burns or when they seek medical advice for slowly healing wounds or foot ulcers. Foot ulcerations may appear due to permanent pressure, such as long walks or badly fitting shoes. Minor wounds or blisters may then lead to deep foot ulcerations. Once infection occurs, complications such as inflammation and destruction of the underlying bones may follow. Affected individuals who do not lose sensation may experience spontaneous pain. In addition, many affected individuals exhibit, to a variable degree, symmetrical distal muscle weakness and wasting.

HSAN I is characterized by marked sensory disturbances mainly as the loss of pain and temperature sensation in the distal parts of the lower limbs. The loss of sensation can also extend to the proximal parts of the lower limbs and the upper limbs as the disease progresses. Some affected individuals do not lose sensation, but instead experience severe shooting, burning, and lancinating pains in the limbs or in the trunk. Autonomic disturbances, if present, manifest as decreased sweating. The degree of motor disturbances is highly variable, even within families, ranging from absent to severe distal muscle weakness and wasting.

The disease progresses slowly, but often disables the affected individuals severely after a long duration. The onset of the disease varies between the 2nd and 5th decade of life, albeit congenital or childhood onset has occasionally been reported. With the progression of the disease, the affected individuals lose the ability to feel pain in their feet and legs. Minor injuries in the painless area can result in slow-healing wounds which, if not immediately recognized, can develop into chronic ulcerations. Once infection occurs, these ulcerations can result in severe complications that lead to foot deformity, such as inflammation of the underlying bones, spontaneous bone fractures, and progressive degeneration of weight-bearing joints. Furthermore, foot deformity promotes skin changes such as hyperkeratosis at pressure points. These complications may necessitate amputation of the affected foot.

Biopsies of severely affected sural nerve (short saphenous nerve) in patients with HSAN I showed evidence of neuronal degeneration. Only a very few myelinated fibers were observed some of which showed a sign of primary (segmental) demyelination. A reasonable number of unmyelinated axons remained, although the presence of stacks of flattened Schwann cell processes suggested unmyelinated axon loss. Electrophysiological testing provides additional evidence that neuronal degeneration underlies the disease. Sensory potentials are usually absent in the lower limbs but are often recordable or even normal in the upper limbs of the patients. In addition, motor conduction is slow, possibly implying a demyelinating process.

Hereditary sensory and autonomic neuropathy type I (HSAN I) or hereditary sensory neuropathy type I (HSN I) is a group of autosomal dominant inherited neurological diseases that affect the peripheral nervous system particularly on the sensory and autonomic functions. The hallmark of the disease is the marked loss of pain and temperature sensation in the distal parts of the lower limbs. The autonomic disturbances, if present, manifest as sweating abnormalities.

The beginning of the disease varies between adolescence and adulthood. Since affected individuals cannot feel pain, minor wounds or blisters in the painless area may not be immediately recognized and can develop into extensive and deep foot ulcerations. Once infection occurs, the complications such as inflammation and progressive destruction of the underlying bones may follow and may require amputation of the surrounding area.

HSAN I is the most common type among the five types of HSAN. As a heterogeneous group of diseases, HSAN I can be divided into five subtypes HSAN IA-E. Most of the genes associated with the diseases have been identified. However, the molecular pathways leading to the manifestation of the diseases are not fully understood. Therefore, the potential targets for therapeutic interventions are not known. Moreover, gene-based therapies for patients with the diseases are not available to date, hence supportive care is the only treatment available for the patients.

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.

The diagnosis of PMD is often first suggested after identification by magnetic resonance imaging (MRI) of abnormal white matter (high T2 signal intensity, i.e. T2 lengthening) throughout the brain, which is typically evident by about 1 year of age, but more subtle abnormalities should be evident during infancy. Unless there is a family history consistent with sex-linked inheritance, the condition is often misdiagnosed as cerebral palsy. Once a "PLP1" or "GJA12" mutation is identified, prenatal diagnosis or preimplantation genetic diagnostic testing is possible.

Pelizaeus–Merzbacher disease (PMD) is a rare central nervous system disorder in which coordination, motor abilities, and intellectual function are delayed to variable extents.

SCA6 is typified by progressive and permanent cerebellar dysfunction. These cerebellar signs include ataxia and dysarthria, likely caused by cerebellar atrophy. Prior to diagnosis and the onset of major symptoms, patients often report a feeling of "wooziness" and momentary imbalance when turning corners or making rapid movements. The age at which symptoms first occur varies widely, from age 19 to 71, but is typically between 43 and 52. Other major signs of SCA6 are the loss of vibratory and proprioceptive sensation and nystagmus.

While most patients present with these severe progressive symptoms, others, sometimes within the same family, display episodic non-progressive symptoms more similar to episodic ataxia. Still others present with symptoms common to both SCA6 and familial hemiplegic migraine.

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.

Hereditary gelsolin amyloidosis is a cutaneous condition inherited in an autosomal dominant fashion.

The condition was first described in 1969, by the Finnish ophthalmologist Jouko Meretoja, and is also known as Familial amyloid neuropathy type IV, Meretoja syndrome, Hereditary amyloidosis, Finnish type.

The disorder primarily associated with eye, skin and cranial nerve symptoms. It is a form of amyloidosis, where the amyloid complexes are formed from fragments of the protein gelsolin in the plasma, due to a mutation in the GSN gene (c.654G>A or c.654G>T).

The most common presentation of Milroy Disease is bilateral lower extremity lymphedema, and may also be accompanied by hydrocele.

Non-progressive congenital ataxia (NPCA) is a non-progressive form of cerebellar ataxia which can occur with or without cerebellar hypoplasia.

Fitzsimmons–Guilbert syndrome is an extremely rare genetic disease characterized by a slowly progressive spastic paraplegia, skeletal anomalies of the hands and feet with brachydactyly type E, cone-shaped epiphyses, abnormal metaphyseal–phalangeal pattern profile, sternal anomaly (pectus carinatum or excavatum), dysarthria, and mild intellectual deficit.

Paraplegia is an impairment in motor or sensory function of the lower extremities. The word comes from Ionic Greek παραπληγίη "half-striking". It is usually caused by spinal cord injury or a congenital condition that affects the neural (brain) elements of the spinal canal. The area of the spinal canal that is affected in paraplegia is either the thoracic, lumbar, or sacral regions. Common victims of this impairment are veterans or members of the armed forces. If four limbs are affected by paralysis, tetraplegia or quadriplegia is the correct term. If only one limb is affected, the correct term is monoplegia.

Spastic paraplegia is a form of paraplegia defined by spasticity of the affected muscles, rather than flaccid paralysis.

The American Spinal Injury Association classifies spinal cord injury severity. ASIA A being the complete loss of sensory function and motor skills below the injury. ASIA B is having some sensory function below the injury, but no motor function. ASIA C some motor function below level of injury, but half the muscles cannot move against gravity. ASIA D, more than half of the muscles below the level of injury can move against gravity. ASIA E which is the restoration of all neurologic function.

Neuroimaging like MRI is important. However, there was considerable intrafamilial variability regarding neuroimaging, with some individuals showing normal MRI findings. Early individual prognosis of such autosomal recessive cerebellar ataxias is not possible from early developmental milestones, neurological signs, or neuroimaging.

With so few described cases, establishing the basic pathophysiological mechanisms or genetic abnormalities has not been possible.

Dennie–Marfan syndrome is a syndrome in which there is association of spastic paraplegia of the lower limbs and mental retardation in children with congenital syphilis. Both sexes are affected, and the onset of the disease can be acute or insidious, with slow progression from weakness to quadriplegia. Epilepsy, cataract, and nystagmus may be also be found.

The syndrome was described by Charles Clayton Dennie in 1929, and Antoine Marfan in 1936.

People with the spastic/spasticity type of CP are hypertonic—i.e., they present with very stiff and tight muscle groups, far greater than typical humans—and have what is essentially a neuromuscular mobility impairment (rather than hypotonia or paralysis) which stems from an upper motor neuron lesion in the brain. The corticospinal tract or the motor cortex may be secondarily affected.

Spastic muscles are continuously contracting, or "tight", because the corresponding nerves permanently over-fire the command to tighten. This is caused by their inability to properly absorb GABA, or gamma amino butyric acid. The tightness, in addition to restricting movement, also acts as an overwhelming opposing force to neighbouring muscles and joints, eventually leaving the entire skeleton deformed compared to normal skeletal, bone, and joint structure in people without spasticity. Abnormal postures are usually associated with the antigravity muscles, which are extensors in the leg and the flexors in the arm. Deformities of joints develop which may become joint contractures, or "fixed contractures", with time.

Changes in spasticity and corresponding postures may also occur with other brain activity, such as excitement, fear or anxiety, or even pain, which increase muscle tension.

A person with spastic CP will commonly show, in addition to higher muscle tone, persistent primitive reflexes, greater stretch reflexes, plantar reflex, and ankle clonus.

A third of people with cerebral palsy have seizures - this is most common in spastic CP.

Persons with HDLS can suffer from tremors, decreased body movement, unsteadiness (Parkinsonism, muscles on one side of the body in constant contraction (spastic hemiparesis), impairment in motor and sensory function in the lower extremities (paraparesis), paralysis resulting in partial or total loss of all extremities and torso (tetraparesis), and the lack of voluntary coordination of muscle movements (ataxia).

Spinocerebellar ataxia type 6 (SCA6) is a rare, late-onset, autosomal dominant disorder, which, like other types of SCA, is characterized by dysarthria, oculomotor disorders, peripheral neuropathy, and ataxia of the gait, stance, and limbs due to cerebellar dysfunction. Unlike other types, SCA 6 is not fatal. This cerebellar function is permanent and progressive, differentiating it from episodic ataxia type 2 (EA2) where said dysfunction is episodic. In some SCA6 families, some members show these classic signs of SCA6 while others show signs more similar to EA2, suggesting that there is some phenotypic overlap between the two disorders. SCA6 is caused by mutations in CACNA1A, a gene encoding a calcium channel α subunit. These mutations tend to be trinucleotide repeats of CAG, leading to the production of mutant proteins containing stretches of 20 or more consecutive glutamine residues; these proteins have an increased tendency to form intracellular agglomerations. Unlike many other polyglutamine expansion disorders expansion length is not a determining factor for the age that symptoms present.

With symptoms of personality changes, behavioral changes, dementia, depression, and epilepsy, HDLS has been commonly misdiagnosed for a number of other diseases. Dementia or frontotemporal behavioral changes, for example, have commonly steered some clinicians to mistakenly consider diagnoses such as Alzheimer’s disease, frontotemporal dementia or atypical Parkinsonism. The presence of white matter changes has led to misdiagnosis of multiple sclerosis. HDLS commonly manifests with neuropsychiatric symptoms, progressing to dementia, and after a few years shows motor dysfunction. Eventually patients become wheelchair-bound or bedridden.

White matter degeneration is associated with and makes differential diagnoses out of other adult onset leukodystrophies such as metachromatic leukodystrophy (MLD), Krabbe disease (globoid cell leukodystrophy), and X-linked adrenoleukodystrophy (X-ADL).

Upington disease, also called Perthes-like hip disease, enchondromata, ecchondromata, and familial dyschondroplasia, is an extremely rare autosomal dominant malformation disorder. It has only one published source claiming its existence in three generations of one family from South Africa.

Symptoms of MJD are memory deficits, spasticity, difficulty with speech and swallowing, weakness in arms and legs, clumsiness, frequent urination and involuntary eye movements. Symptoms can begin in early adolescence and they get worse over time. Eventually, MJD leads to paralysis; however, intellectual functions usually remain the same.