NORD gratefully acknowledges John K. Fink, MD, Professor, Department of Neurology, University of Michigan; Medical Advisor, Spastic Paraplegia Foundation, for the preparation of this report.
The hereditary spastic paraplegias (HSP) are a large group of inherited neurologic disorders that share the primary symptom of difficulty walking due to muscle weakness and muscle tightness (spasticity) in the legs. There are more than 80 different genetic types of HSP.
There may be significant variation in the severity of leg weakness (varying from none to marked), the degree of spasticity (varying from minimal to severe), and the occurrence of other neurologic symptoms between different genetic types of HSP; as well differences in the nature and severity of symptoms between individuals who have exactly the same genetic type of HSP.
For additional reviews of HSP including molecular pathogenesis, please refer to references 1 through 4 and Online Mendelian Inheritance in Man (www.omim.org).
Various types of HSP are classified according to a) the mode of inheritance (dominant, recessive, X-linked, maternal); b) the gene in which the mutation occurs; and c) the clinical syndrome (pattern of symptoms and neurologic findings). HSP syndromes are classified as “uncomplicated” when symptoms are confined to leg weakness and tightness and urinary urgency. HSP syndromes are classified as “complicated” when leg weakness and tightness (spasticity) are accompanied by other neurologic disturbance such as peripheral nerve impairment, muscle atrophy, or intellectual impairment.
There are more than 80 genetic types of HSP. The chromosome locations (“loci”) of HSP genes are designated “SPastic parapleGia, loci (“SPG”) and numbered in order of their discovery (for example, SPG1 through SPG80).
Symptoms describe an individual’s experience of a medical disorder. Signs are the objective evidence of the disorder, documented, for example by physician examination, laboratory studies, or magnetic resonance images (MRI). The primary symptom of HSP is difficulty walking due to weakness and tightness (spasticity) in the legs. Both legs are affected, usually to a relatively similar degree.
The term “paraplegia” means severe weakness in both legs including paralysis. “Paraparesis” indicates weakness in both legs of lesser severity than paraplegia. Although the disorder is typically referred to as hereditary spastic paraplegia the degree of weakness is variable and ranges from no weakness (full strength) to marked weakness (paraplegia).
When present, weakness does not affect all leg muscles, but rather is most obvious in muscles of hip flexion (iliopsoas), hip abduction (gluteus medius), knee flexion (hamstrings), and foot dorsiflexsion (bending the foot back toward the shin via tibialis anterior muscle). In contrast, muscles of leg extension (quadriceps) and foot extension (gastrocnemius-soleus) usually are not affected in uncomplicated HSP.
Spasticity primarily affects muscles of leg extension (quadriceps), knee flexion (hamstrings), hip adduction (bringing the knees together, thigh adductor muscles), and muscles that extend the feet (gastrocnemius-soleus [Achilles tendon]).
Walking pattern described as “spastic gait” occurs in which the following elements are present, each to variable degree in different individuals: a) heel strike is shifted forward (landing on the mid-foot or even further forward on the balls of the feet); b) there is reduced foot dorsiflexion (not bending the toes up, but instead tending to drag the toes, often catching them on carpet or when stepping over curbs, and causing the toes of the shoes to be worn out); c) stride length may become shorter; d) there may be “circumduction” or “scissoring”, with one leg crossing into the path of the other; e) there is a tendency for the knees to be maintained flexed (not fully extended in mid-stride), f) for thighs to be close together (adductor tightness), and g) hip flexion (knee lifting) to be reduced. Balance difficulty, often worse when walking in the dark or on uneven surfaces is not uncommon in individuals with HSP.
Tightness in the legs and leg muscle spasm (often at night) are not uncommon.
The consequences of abnormal walking pattern cause strain on the ankles, knees, hips, and back and often cause pain in these areas.
Urinary urgency, the symptom of experiencing a very short interval between the sensation of need to urinate and difficulty remaining continent, is very common in HSP and occasionally may be an early symptom. Bowel urgency is less common but may occur. Medications such as oxybutynin may reduce urinary urgency. If urinary urgency is severe or accompanied by difficulty initiating urination, consultation with a urologist is recommended.
Some genetic types of HSP tend to cause only spastic weakness in the legs and urinary urgency. These syndromes are referred to as “uncomplicated HSP”. Other genetic types of HSP tend to be associated with additional symptoms (“complicated HSP”) including difficulty with coordination (“ataxia”), impaired vision, seizures (epilepsy), muscle atrophy, disturbance of the nerves in the arms and legs (neuropathy), and disturbance cognitive ability (intellectual impairment and dementia). Previously, it was considered that HSP caused symptoms only in the legs, and therefore, did not affect the strength or coordination of the arms and hands, or speech or swallowing. As the number of HSP types has grown, it is now recognized that the arms, hands, and speech and swallowing may be affected in some genetic types of complicated HSP
When HSP begins in very early childhood (before age two years, for example), symptoms may not worsen even over many years or decades. Individuals with this “non-progressive” (non-worsening) pattern may resemble subjects with spastic cerebral palsy, a life-long disorder that also remains relatively stable. One caveat however: although early childhood-onset forms of HSP may be “non-progressive”, the degree of spasticity may increase slowly if adequate range-of-motion is not maintained through stretching exercises and muscle spasticity reduction.
In contrast, when HSP symptoms begin after early childhood (in adolescence or adulthood), symptoms usually worsen very slowly over a number of years. Sudden onset or rapid worsening over weeks or months is not typical of HSP and suggests an alternate disorder or co-existing condition. After a number of years of very gradual worsening, the rate of worsening appears to slow down for many (not all) subjects. These subjects seem to reach a “functional plateau” beyond which the degree of worsening seems to be similar to that expected for age and similar degrees of physical exercise. Nonetheless, not all patients reach an apparent “leveling off” or functional plateau but instead experience continuous worsening of walking ability due to very slowly progressive muscle weakness and tightness .
There may be significant variability in the type of symptoms and their severity. For example, symptoms may remain mild in some patients or become quite severe in others patients. This variability may occur between different genetic types of HSP as well as in between individuals with the same genetic type of HSP including family members who share not only the same genetic type of HSP but also precisely the same genetic mutation.
There is not a perfect correlation between the genetic type of HSP and the pattern of symptoms. For example, while some genetic types of HSP (e.g. dominantly inherited HSP due to SPG4/spastin mutation) usually are associated with “uncomplicated” HSP syndromes, some patients with these types of HSP develop additional neurologic symptoms. As another example, although SPG7 and SPG11 typically are associated with additional neurologic symptoms (ataxia, neuropathy, cognitive impairment, for example), some subjects with mutations in these genes have uncomplicated HSP (only spastic weakness in the legs). There also may be variation in severity and the nature of symptoms between affected family members. Therefore, it is generally not possible to predict with certainty the severity or exact nature of symptoms associated with given genetic type of HSP. A cautious, “wait and see” approach, combined with pro-active, individualized physical therapy is recommended.
Prognosis: predicting symptoms and course of HSP
As noted above, there is significant variation in HSP symptoms and their severity. This limits the certainty of making predictions. In general however, some genetic types of HSP are usually associated with only leg weakness, spasticity, and urinary urgency (“uncomplicated HSP”). Other types of HSP are usually associated with other neurologic disturbances in addition to these symptoms (“complicated HSP”). Although there are exceptions (discussed above), an individual with a genetic type of HSP usually associated with “uncomplicated” syndrome would be expected to have only spastic weakness and urinary urgency.
Symptoms of HSP vary from mild to severe. Individuals with severe symptoms may be unable to walk independently. In general, however, HSP does not shorten lifespan.
As with all inherited disorders, the HSPs are due to gene mutations. Each genetic type of HSP is due to a mutation in a specific “HSP gene”. For example, mutations in SPG3A/atlastin, SPG4/spastin, and SPG7/paraplegin genes cause SPG3A, SPG4, and SPG7 HSP, respectively.
Depending on the genetic type of HSP, HSP may be transmitted to offspring (and inherited from parents) as dominant, recessive, X-linked, and “maternal” traits. The various genetic types of HSP and their inheritance patterns are summarized in the table below.
The following discussion of inheritance patterns is intended as an overview. Individuals seeking genetic counseling for HSP are recommended to consult a genetic counselor or medical geneticist for specific information. In general, dominantly inherited forms of HSP can be transmitted by (or inherited from) an individual who has the disorder. In general, each child of an individual who has a dominantly inherited form of HSP has a 50% chance of inheriting the gene mutation and a similar (approximately 50% chance) of developing the condition. Occasionally, dominantly inherited HSP “skips” a generation. (i.e. genetic penetrance is very high, exceeding 90%, but is occasionally incomplete). Although the chance of inheriting the condition can be estimated, it is difficult to predict with certainty the age at which symptoms would begin or their severity. There may be significant differences in the severity of the disorder between family members.
For recessively inherited forms of HSP, both parents are usually carriers of the gene mutation and usually do not have symptoms (there are exceptions to this generalization: occasionally, parents who are carriers of some forms of recessively inherited HSP have had symptoms of HSP). In general, if one individual in a family has a recessively inherited disorder, each of this individual’s full siblings (for example, another child in this family) has approximately a 25% chance of having the same disorder. In general, individuals who have recessively inherited disorders do not transmit the disorder to their children. There have been some reported exceptions to this however.
X-linked disorders are transmitted from women to their sons. Daughters may carry X-linked gene mutations, but like their mothers, usually do not have symptoms although they may have mild symptoms and rarely, may have more significant symptoms of the disorder.
Maternally transmitted disorders are those in which the gene mutation involves a mitochondrial gene, are transmitted from mothers to sons or daughters (not transmitted from males).
Underlying causes of HSP: Each of the more than 80 genetic types of HSP is due to mutations in a different gene. These genes encode proteins that have diverse molecular functions including movement of chemicals from one part of the cell to another (“axon transport”), energy production (“mitochondrial disturbance”), and disorders of specific lipid metabolism, among others. [1,4]
Disturbance in some of these functions appears to lead to altered nerve cell (neuron) development. For these types of HSP, the disorder is not a degenerative process, but rather a developmental disturbance in which the formation of selected nerve pathways during intra-uterine development was abnormal.
For other genetic types, HSP gene mutations cause the ends of very long nerve processes (axons) to slowly degenerate within the spinal cord. This impairs nerve transmission from the brain through the spinal cord. To be clear, the entire spinal cord is not degenerating. Rather, the abnormalities in HSP appear to selectively affect only specific nerve pathways, particularly the very long nerve processes (axons) that carry signals from the brain motor cortex to the lower part of the thoracic spinal cord. In some types, this disturbance is not limited to the spinal cord but also affects nerves in the legs (and arms, to a lesser extent). This latter process is termed “peripheral neuropathy”.
HSP is diagnosed by the following: 1) typical symptoms (lower extremity spastic weakness that may be non-worsening (early childhood onset) or slowly progressive over many years; 2) findings on neurologic examination (lower extremity hyperreflexia usually accompanied by some degree of spasticity and sometimes a specific pattern of muscle weakness); and 3) by the exclusion of alternate disorders (by history, examination, neuroimaging, and laboratory studies as needed).
The occurrence of similarly affected family members is helpful in recognizing HSP but is not required for the diagnosis of HSP. Many individuals with HSP do not have similarly affected family members. Such individuals could represent the first occurrence of a genetic mutation (“de novo mutation”). Depending on the genetic type of HSP (dominant, recessive, X-linked, or maternal transmission), there may be a possibility that the disorder could be transmitted to the offspring of these individuals. Genetic testing is often helpful in confirming the clinical diagnosis of HSP and in determining the genetic type of HSP. Results of genetic testing can be used, together with clinical information, to provide genetic counseling.
Neurologic examination is important for patients with symptoms of HSP. First, this establishes the diagnosis and excludes alternative and co-existing disorders, some of which may have specific treatments. Second, neurologic examination helps identify the specific features of an individual’s walking disturbance. Knowing which specific muscles need strengthening, which specific muscles need spasticity-reduction (through medication, Botox injection, and stretching), and the degree of impairment of balance, speed, and precision of movement helps neurologists and physiatrists develop a proactive therapy approach to improve and maintain the ability to walk; and limit the cumulative impact of abnormal walking patterns on ankles, knees, hips, and spine.
Laboratory tests, neurophysiologic testing, and neuroimaging: Routine laboratory studies (such as blood counts, serum electrolytes, and tests of kidney, liver, and endocrine functions) including analysis of cerebrospinal fluid (obtained by “spinal tap”) are normal in most types of HSP. The primary role of such testing is to help exclude alternate and co-existing diagnoses.
MRI scans of the brain and spinal cord are important in diagnosing HSP because they help exclude other disorders such as multiple sclerosis and structural abnormalities of the brain and spinal cord. Routine magnetic resonance imaging (MRI) of the brain is usually normal in uncomplicated HSP, and, depending on the genetic type and its neurologic features, in many forms of complicated HSP. In contrast to routine brain MRI, which is usually normal in uncomplicated HSP, special MRI techniques such as diffusion tensor imaging, reserved primarily for research purposes often show more widespread nerve pathway abnormalities in uncomplicated and complicated HSP.
In contrast to the typically normal brain MRI in subjects with uncomplicated HSP, there are many types of complicated HSP in which brain MRI demonstrates specific abnormalities including reduced size of the corpus callosum (a structure containing nerve fibers that transit from one brain hemisphere to the other).Thin corpus callosum is a frequent (but not constant) feature of SPG11 and SPG15 and has also been present in many other types of HSP (including SPG3A, SPG4, SPG7, SPG15, SPG21, SPG32, SPG47, PG49, SPG54, and SPG56). (2,5) In addition to thin corpus callosum, many genetic types of HSP have abnormal appearing brain white matter (e.g. due SPG5/CYPB7, SPG7/paraplegin, SPG21/maspardin, and SPG35/FA2H gene mutations). [2,5]
Spinal cord MRI scan in HSP is usually normal although may show somewhat smaller diameter of the thoracic spinal cord. 
Genetic testing: Testing for HSP genes is available and performed for individual HSP genes, for panels containing dozens of HSP genes, and by analysis of all genes (whole exome and whole genome analysis). Genetic testing is often helpful to confirm the clinical diagnosis of HSP. Genetic testing is most often able to find causative gene mutations for subjects with HSP who have a family history of a similarly affected first-degree relative.
Despite discovery of more than 60 genes in which mutations cause various types of HSP, many individuals with HSP do not have an identified gene mutation. This is because: a) genes for all types of HSP have not been discovered and furthermore, some discovered genes are not yet included in clinical testing panels; b) methods of gene sequencing typically used to analyze large panels of genes do not analyze all regions of genes. Furthermore, while sensitively detecting gene sequence changes, these “next generation sequencing” methods are less sensitive in detecting gene insertions and deletions that do not change the sequence of the remaining portion of the gene.
Genetic testing is expensive and not all insurance companies provide reimbursement for this analysis. Identifying a causative gene mutation can bring closure to a diagnostic odyssey, contribute insight into the prognosis and can be applied to genetic counseling and prenatal diagnosis. Nonetheless at present, genetic testing results very rarely influence treatment which is largely directed toward reducing symptoms.
Interpreting HSP genetic test results may be straightforward. Genetic testing may identify a gene mutation that is known to be associated with HSP in other subjects, absent in unaffected subjects, and known or predicted to change the protein function. These mutations are termed “likely pathogenic” (likely to be disease causing). On the other hand, genetic testing may also identify gene variations that are considered normal variations (for example, they may be present in subjects who do not have HSP and may be predicted to not change the protein function). Such mutations are considered “benign” variations and are not likely to cause HSP.
In addition to “likely pathogenic” and “likely benign” mutations”, it is not uncommon for genetic testing to identify gene variations that are “of uncertain significance”. Such mutations may not have been reported to be associated with the disorder or may not be predicted to disturb the function of the protein. By definition, it is not known if gene variations of uncertain significance cause HSP (i.e. are pathogenic) or are actually normal variations that are of no medical consequence. Individuals seeking more information regarding results of genetic testing are recommended to consult a medical geneticist or genetic counselor.
Treatment: management of symptoms
Despite encouraging progress in many research laboratories (see reference 7 for example), treatment for HSP is presently limited to reducing symptoms of muscle weakness, spasticity, and urinary urgency.
A pro-active regimen of daily physical exercise, guided by physical therapist or personal trainer and developed for each patient’s unique constellation of symptoms is recommended. This recommendation is based not on peer-reviewed scientific publications but rather on the reports of large numbers of HSP subjects who state that exercise helps and that periods of reduced exercise are associated with increased symptoms. HSP symptoms are variable. One type of exercise may not benefit all individuals. Exercise programs should be developed by a neurologist, physiatrist, physical therapist or personal trainer who is experienced with HSP or similar disorders and should focus on the specific factors that make walking difficult for the specific individual. Individuals are advised to consult their primary care physician before beginning exercise programs, to begin with low intensity, increase slowly, set small goals, keep records of their progress, add variety, and be creative.
Exercise goals are to 1) improve and maintain cardiovascular fitness; 2) reverse the reduced functional capacity, stiffness, and weakness due to relatively sedentary lifestyle that often accompanies chronic gait disorders and which are superimposed on walking disturbance due to HSP; 3) improve the mechanics of walking, facilitate neurologic circuits underlying walking reflexes, reduce falling, and maintain bone and joint fitness; and 4) maximize an individual’s independence and sense of control.
For some patients, weakness in certain muscles is the most significant factor making walking difficult. For these patients, daily exercise programs should focus on resistance exercises designed to maintain and very gradually increase the strength of these weak muscles. For others, spasticity is a more significant factor than weakness in limiting the ability to walk. For these patients, stretching exercises and muscle relaxant medication may be more beneficial than muscle strengthening exercises alone. A variety of exercises is recommended including walking, for example in shallow swimming pool, water aerobics, swimming, bicycling (including pedaling in reverse to exercise the strength and speed of hip flexion), yoga, dance, core exercises, balance exercises, and therapeutic horseback riding.
Patients with significant degrees of spasticity may benefit from medications such as Lioresal. In general, reducing spasticity through medication improves walking primarily when spasticity, not weakness is the primary factor limiting the ability to walk. When weakness is the major factor, markedly reducing spasticity (e.g. through intrathecal Lioresal pump) may make the legs very relaxed (even hypotonic or “floppy”) but actually make walking and standing more difficult. Patients considering intrathecal baclofen pumps should undergo at least one trial in which the important criteria is not simply if spasticity reduction occurred, but rather if spasticity reduction resulted in improved walking ability. Botulinum toxin (“Botox”) injection may be helpful when muscle tightness particular affects a limited number of muscles (e.g. adductors or ankles). Oxybutynin and related medications may reduce urinary urgency. Individuals with more advanced bladder or bowel symptoms are recommended to consult urology or gastroenterology specialists, respectively.
Ankle-foot orthotics may be useful to reduce the tendency for the feet to be extended (toes down) causing toe dragging and tripping. Ankle-foot orthotics are often used in combination with medications (e.g. Lioresal or Botox) that reduce muscle spasticity.
There have been rapid advances in our knowledge of the causes of HSP. Discovery of dozens of genes implicated in HSP is providing insight into molecular pathways involved. Gene discoveries have permitted development of diverse animal models (in mice, rats, fruit flies, zebrafish, C. elegans) in which to explore disease mechanisms and potential treatments. Parallel advances in gene transfer (gene therapy) and gene modification (e.g. utilizing CRISPR/Cas9 methods) approaches offer additional treatment strategies. Nonetheless, the process of drug discovery, development, and testing takes many years. Until (and even after) specific treatments become widely available, individuals with HSP are recommended to pursue active lifestyles including physical rehabilitation in order to maintain and improve functional abilities and cardiovascular fitness.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
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Some current clinical trials also are posted on the following page on the NORD website:
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For information about clinical trials conducted in Europe, contact:
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2. Fink JK. Upper Motor Neuron Disorders: Hereditary Spastic Paraplegia and Primary Lateral Sclerosis. In: Johnson MV, Adams HP, Fatemi A, eds. Neurobiology of Disease.Oxford University Press, 2016.
3. Parodi L, Fenu S, Stevanin G, Durr A. Hereditary spastic paraplegia: More than an upper motor neuron disease. Rev Neurol (Paris) 2017 May;173:352-360.
4. Novarino G, Fenstermaker AG, Zaki MS, et al. Exome sequencing links corticospinal motor neuron disease to common neurodegenerative disorders. Science 2014 Jan 31;343:506-511.
5. Fink JK. The Hereditary Spastic Paraplegias. In: Rosenberg R, ed. Molecular and Genetic Basis of Neurologic and Psychiatric Disease, 5th edition ed Lippincott Williams & Wilkins, 2014.
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7. Julien C, Lissouba A, Madabattula S, et al. Conserved pharmacological rescue of hereditary spastic paraplegia-related phenotypes across model organisms. Hum Mol Genet 2016 Mar 15;25:1088-1099.
8. Fink JK. Hereditary Spastic Paraplegias. In: Schapira AHV, ed. Neurology and Clinical Neurosciences. Philadelphia: Mosby Elsevier, 2007:899-910.
9. Fink JK. Hereditary spastic paraplegia: clinico-pathologic features and emerging molecular mechanisms. Acta Neuropathol 2013 Sep;126:307-328.
Paik NJ, Lim JY. Hereditary Spastic Paraplegia. Medscape. Updated: Apr 15, 2016. Available at: http://emedicine.medscape.com/article/306713-overview Accessed June 21, 2017.
Fink JK. Hereditary Spastic Paraplegia Overview. 2000 Aug 15 [Updated 2014 Feb 6]. In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2017. Available from: https://www.ncbi.nlm.nih.gov/books/NBK1509/ Accessed June 21, 2017.
National Institute of Neurological Disorders and Stroke. Hereditary Spastic Paraplegia Information Page. Available at: https://www.ninds.nih.gov/Disorders/All-Disorders/Hereditary-Spastic-Paraplegia-Information-Page Accessed June 21, 2017.
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