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Hereditary spastic paraplegia

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Hereditary spastic paraplegia
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Hereditary spastic paraplegia (HSP) is a group of inherited diseases whose main feature is a progressive gait disorder. The disease presents with progressive stiffness (spasticity) and contraction in the lower limbs.[1] HSP is also known as hereditary spastic paraparesis, familial spastic paraplegia, French settlement disease, or Strumpell-Lorrain disease. The symptoms are a result of dysfunction of long axons in the spinal cord. The affected cells are the primary motor neurons, therefore the disease is an upper motor neuron disease.[2] HSP is not a form of cerebral palsy even though it physically may appear and behave much the same as spastic diplegia. The origin of HSP is different from cerebral palsy. Despite this, some of the same anti-spasticity medications used in spastic cerebral palsy are sometimes used to treat HSP symptoms.

HSP is caused by defects in transport of proteins, structural proteins, cell maintaining proteins, lipids, and other substances through the cell. Long nerve processes (axons) are affected because long distances make nerve cells particularly sensitive to defects in these mentioned mechanisms.[3][4]

The disease was first mentioned in 1876[5] by Adolph Seeligmüller, a German neurologist, who described a family of four affected children with spasticity. Further cases were described in 1883[6][7] by Adolph Strümpell, a German neurologist. Those cases were described more extensively in 1888 by Maurice Lorrain, a French physician.[8] Due to their contribution in describing the disease, it is still named Strümpell-Lorrain disease in French speaking countries. The term hereditary spastic paraplegia was coined by Anita Harding in 1983.[9]

Signs and symptoms

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.[10] 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.[11]Disability has been described as progressing more rapidly in adult onset forms.[12]

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.[12] 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.[13]

Anita Harding[9] 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.[9] Some of the genes listed below have been described in other diseases than HSP before. Therefore, some key genes overlap with other disease groups.

Age of onset

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.[14] 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.[14] This was also described earlier, that later onset forms evolve more rapidly.[12]

Cause

HSP is a group of genetic disorders. It follows general inheritance rules and can be inherited in an autosomal dominant, autosomal recessive or X-linked recessive manner. The mode of inheritance involved has a direct impact on the chances of inheriting the disorder. Over 70 genotypes had been described, and over 50 genetic loci have been linked to this condition.[15] Ten genes have been identified with autosomal dominant inheritance. One of these SPG4 accounts for ~50% of all genetically solved cases cases, or approximately 25% of all HSP cases.[14] Twelve genes are known to be inherited in an autosomal recessive fashion. Collectively this latter group account for ~1/3 cases.

Most altered genes have known function, but for some the function haven’t been identified yet. All of them are listed in the gene list below, including their mode of inheritance. Some examples are spastin (SPG4) and paraplegin (SPG7) are both AAA ATPases.[16]

Genotypes

The genes are designated SPG (Spastic gait gene). The gene locations are in the format: chromosome - arm (short or p: long or q) - band number. These designations are for the human genes only. The locations may (and probably will) vary in other organisms. Despite the number of genes known to be involved in this condition ~40% of cases have yet to have their cause identified.[17] In the table below SPG? is used to indicate a gene that has been associated with HSP but has not yet received an official HSP gene designation.

Genotype OMIM Gene symbol Gene locus Inheritance Age of onset Other names and characteristics
SPG1 Template:OMIM2 L1CAM Xq28 X-linked recessive Early MASA syndrome
SPG2 Template:OMIM2 PLP1 Xq22.2 X-linked recessive Variable Pelizaeus–Merzbacher disease
SPG3A Template:OMIM2 ATL1 14q22.1 Autosomal dominant Early Strumpell disease
SPG4 Template:OMIM2 SPAST 2p22.3 Autosomal dominant Variable
SPG5A Template:OMIM2 CYP7B1 8q12.3 Autosomal recessive Variable
SPG6 Template:OMIM2 NIPA1 15q11.2 Autosomal dominant Variable
SPG7 Template:OMIM2 SPG7 16q24.3 Autosomal dominant Variable
SPG8 Template:OMIM2 KIAA0196 8q24.13 Autosomal dominant Adult
SPG9A Template:OMIM2 ALDH18A1 10q24.1 Autosomal dominant Teenage Cataracts with motor neuronopathy, short stature and skeletal abnormalities
SPG9B Template:OMIM2 ALDH18A1 10q24.1 Autosomal recessive Early
SPG10 Template:OMIM2 KIF5A 12q13.3 Autosomal dominant Early
SPG11 Template:OMIM2 SPG11 15q21.1 Autosomal recessive Variable
SPG12 Template:OMIM2 RTN2 19q13.32 Autosomal dominant Early
SPG13 Template:OMIM2 HSP60 2q33.1 Autosomal dominant Variable
SPG14 Template:OMIM2 ? 3q27–q28 Autosomal recessive Adult
SPG15 Template:OMIM2 ZFYVE26 14q24.1 Autosomal recessive Early
SPG16 Template:OMIM2 ? Xq11.2 X-linked recessive Early
SPG17 Template:OMIM2 BSCL2 11q12.3 Autosomal dominant Teenage
SPG18 Template:OMIM2 ERLIN2 8p11.23 Autosomal recessive Early
SPG19 Template:OMIM2 ? 9q Autosomal dominant Adult onset
SPG20 Template:OMIM2 SPG20 13q13.3 Autosomal recessive Early onset Troyer syndrome
SPG21 Template:OMIM2 ACP33 15q22.31 Autosomal recessive Early onset MAST syndrome
SPG22 Template:OMIM2 SLC16A2 Xq13.2 X-linked recessive Early onset Allan–Herndon–Dudley syndrome
SPG23 Template:OMIM2 RIPK5 1q32.1 Autosomal recessive Early onset Lison syndrome
SPG24 Template:OMIM2 ? 13q14 Autosomal recessive Early onset
SPG25 Template:OMIM2 ? 6q23–q24.1 Autosomal recessive Adult
SPG26 Template:OMIM2 B4GALNT1 12q13.3 Autosomal recessive Early onset
SPG27 Template:OMIM2 ? 10q22.1–q24.1 Autosomal recessive Variable
SPG28 Template:OMIM2 DDHD1 14q22.1 Autosomal recessive Early onset
SPG29 Template:OMIM2 ? 1p31.1–p21.1 Autosomal dominant Teenage
SPG30 Template:OMIM2 KIF1A 2q37.3 Autosomal recessive Teenage
SPG31 Template:OMIM2 REEP1 2p11.2 Autosomal dominant Early onset
SPG32 Template:OMIM2 ? 14q12–q21 Autosomal recessive Childhood
SPG33 Template:OMIM2 ZFYVE27 10q24.2 Autosomal dominant Adult
SPG34 Template:OMIM2 ? Xq24–q25 X-linked recessive Teenage/Adult
SPG35 Template:OMIM2 FA2H 16q23.1 Autosomal recessive Childhood
SPG36 Template:OMIM2 ? 12q23–q24 Autosomal dominant Teenage/Adult
SPG37 Template:OMIM2 ? 8p21.1–q13.3 Autosomal dominant Variable
SPG38 Template:OMIM2 ? 4p16–p15 Autosomal dominant Teenage/Adult
SPG39 Template:OMIM2 PNPLA6 19p13.2 Autosomal recessive Childhood
SPG41 Template:OMIM2 ? 11p14.1–p11.2 Autosomal dominant Adolescence
SPG42 Template:OMIM2 SLC33A1 3q25.31 Autosomal dominant Variable
SPG43 Template:OMIM2 C19orf12 19q12 Autosomal recessive Childhood
SPG44 Template:OMIM2 GJC2 1q42.13 Autosomal recessive Childhood/teenage
SPG45 Template:OMIM2 NT5C2 10q24.32–q24.33 Autosomal recessive Infancy
SPG46 Template:OMIM2 GBA2 9p13.3 Autosomal recessive Variable
SPG47 Template:OMIM2 AP4B1 1p13.2 Autosomal recessive Childhood
SPG48 Template:OMIM2 AP5Z1 7p22.1 Autosomal recessive 6th decade
SPG49 Template:OMIM2 TECPR2 14q32.31 Autosomal recessive Infancy
SPG50 Template:OMIM2 AP4M1 7q22.1 Autosomal recessive Infancy
SPG51 Template:OMIM2 AP4E1 15q21.2 Autosomal recessive Infancy
SPG52 Template:OMIM2 AP4S1 14q12 Autosomal recessive Infancy
SPG53 Template:OMIM2 VPS37A 8p22 Autosomal recessive Childhood
SPG54 Template:OMIM2 DDHD2 8p11.23 Autosomal recessive Childhood
SPG55 Template:OMIM2 C12orf65 12q24.31 Autosomal recessive Childhood
SPG56 Template:OMIM2 CYP2U1 4q25 Autosomal recessive Childhood
SPG57 Template:OMIM2 TFG 3q12.2 Autosomal recessive Early
SPG58 Template:OMIM2 KIF1C 17p13.2 Autosomal recessive Within first two decades Spastic ataxia 2
SPG59 Template:OMIM2 USP8 15q21.2 ? Childhood
SPG60 Template:OMIM2 WDR48 3p22.2 ? Infancy
SPG61 Template:OMIM2 ARL6IP1 16p12.3 Autosomal recessive Infancy
SPG62 Template:OMIM2 ERLIN1 10q24.31 Autosomal recessive Childhood
SPG63 Template:OMIM2 AMPD2 1p13.3 Autosomal recessive Infancy
SPG64 Template:OMIM2 ENTPD1 10q24.1 Autosomal recessive Childhood
SPG66 Template:OMIM2 ARSI 5q32 ? Infancy
SPG67 Template:OMIM2 PGAP1 2q33.1 Autosomal recessive Infancy
SPG68 Template:OMIM2 KLC2 11q13.1 Autosomal recessive Childhood SPOAN syndrome
SPG69 Template:OMIM2 RAB3GAP2 1q41 Autosomal recessive Infancy Martsolf syndrome, Warburg Micro syndrome
SPG70 Template:OMIM2 MARS 12q13 ? Infancy
SPG71 Template:OMIM2 ZFR 5p13.3 Childhood
SPG72 Template:OMIM2 REEP2 5q31 Autosomal recessive;
autosomal dominant
Infancy
SPG73 Template:OMIM2 CPT1C 19q13.33 Autosomal dominant Adult
SPG74 Template:OMIM2 IBA57 1q42.13 Autosomal recessive Childhood
SPG75 Template:OMIM2 MAG 19q13.12 Autosomal recessive Childhood
SPG76 Template:OMIM2 CAPN1 11q13 Autosomal recessive Adult
SPG77 Template:OMIM2 FARS2 6p25 Autosomal recessive Childhood
SPG78 Template:OMIM2 ATP13A2 1p36 Autosomal recessive Adult Kufor–Rakeb syndrome
SPG79 Template:OMIM2 UCHL1 4p13 Autosomal recessive Childhood
HSNSP Template:OMIM2 CCT5 5p15.2 Autosomal recessive Childhood Hereditary sensory neuropathy with spastic paraplegia
SPG? SERAC1 6q25.3 Juvenile MEGDEL syndrome
SPG? Template:OMIM2 KY 3q22.2 Autosomal recessive Infancy
SPG? PLA2G6 22q13.1 Autosomal recessive Childhood
SPG? ATAD3A 1p36.33 Autosomal dominant Childhood Harel-Yoon syndrome
SPG? KCNA2 1p13.3 Autosomal dominant Childhood
SPG? Granulin 17q21.31
SPG? POLR3A 10q22.3 Autosomal recessive

Pathophysiology

The major feature of HSP is a length dependent axonal degeneration.[18] These include the crossed and uncrossed corticospinal tracts to the legs and fasciculus gracilis. The spinocerebellar tract is involved to a lesser extent. Neuronal cell bodies of degenerating axons are preserved and there is no evidence of primary demyelination.[15] Loss of anterior horn cells of the spinal cord are observed in some cases. Dorsal root ganglia, posterior roots and peripheral nerves are not directly affected.

HSP affects several pathways in motor neurons. Many genes were identified and linked to HSP. It remains a challenge to accurately define the key players in each of the affected pathways, mainly because many genes have multiple functions and are involved in more than one pathway (Figure).

Overview of HSP pathogenesis on cellular level. Identified affected genes in each pathway are depicted.

Axon pathfinding

Pathfinding is important for axon growth to the right destination (e.g. another nerve cell or a muscle). Significant for this mechanism is the L1CAM gene, a cell surface glycoprotein of the immunoglobulin superfamily. Mutations leading to a loss-of-function in L1CAM are also found in other X-linked syndromes. All of these disorders display corticospinal tract impairment (a hallmark feature of HSP). L1CAM participates in a set of interactions, binding other L1CAM molecules as well as extracellular cell adhesion molecules, integrins, and proteoglycans or intracellular proteins like ankyrins.

The pathfinding defect occurs via the association of L1CAM with neuropilin-1. Neurophilin-1 interacts with Plexin-A proteins to form the Semaporin3A receptor complex. Semaporin3A is then released in the ventral spinal cord to steer corticospinal neurons away from the midline spinal cord/medullary junction. If L1CAM does not work correctly due to a mutation, the cortiocospinal neurons are not directed to the correct position and the impairment occurs.[3]

Lipid metabolism

Axons in the central and peripheral nervous system are coated with an insulation, the myelin layer, to increase the speed of action potential propagation. Abnormal myelination in the CNS is detected in some forms of hsp HSP.[19] Several genes were linked to myelin malformation, namely PLP1, GFC2 and FA2H.[3] The mutations alter myelin composition, thickness and integrity.

Endoplasmic reticulum (ER) is the main organelle for lipid synthesis. Mutations in genes encoding proteins that have a role in shaping ER morphology and lipid metabolism were linked to HSP. Mutations in ATL1, BSCL2 and ERLIN2 alter ER structure, specifically the tubular network and the formation of three-way junctions in ER tubules. Many mutated genes are linked to abnormal lipid metabolism. The most prevalent effect is on arachidonic acid (CYP2U1) and cholesterol (CYP7B1) metabolism, phospholipase activity (DDHD1 and DDHD2), ganglioside formation (B4GALNT-1) and the balance between carbohydrate and fat metabolism (SLV33A1).[3][20][19]

Endosomal trafficking

Neurons take in substances from their surrounding by endocytosis. Endocytic vesicles fuse to endosomes in order to release their content. There are three main compartments that have endosome trafficking: Golgi to/from endosomes; plasma membrane to/from early endosomes (via recycling endosomes) and late endosomes to lysosomes. Dysfunction of endosomal trafficking can have severe consequences in motor neurons with long axons, as reported in HSP. Mutations in AP4B1 and KIAA0415 are linked to disturbance in vesicle formation and membrane trafficking including selective uptake of proteins into vesicles. Both genes encode proteins that interact with several other proteins and disrupt the secretory and endocytic pathways.[19]

Mitochondrial function

Mitochondrial dysfunctions have been connected with developmental and degenerative neurological disorders. Only a few HSP genes encode for mitochondrial proteins. Two mitochondrial resident proteins are mutated in HSP: paraplegin and chaperonin 60. Paraplegin is a m-AAA metalloprotease of the inner mitochondrial membrane. It functions in ribosomal assembly and protein quality control. The impaired chaperonin 60 activity leads to impaired mitochondrial quality control. Two genes DDHD1 and CYP2U1 have shown alteration of mitochondrial architecture in patient fibroblasts. These genes encode enzymes involved in fatty-acid metabolism.

Diagnosis

Initial diagnosis of HSPs relies upon family history, the presence or absence of additional signs and the exclusion of other nongenetic causes of spasticity, the latter being particular important in sporadic cases.[9]

Cerebral and spinal MRI is an important procedure performed in order to rule out other frequent neurological conditions, such as multiple sclerosis, but also to detect associated abnormalities such as cerebellar or corpus callosum atrophy as well as white matter abnormalities. Differential diagnosis of HSP should also exclude spastic diplegia which presents with nearly identical day-to-day effects and even is treatable with similar medicines such as baclofen and orthopedic surgery; at times, these two conditions may look and feel so similar that the only perceived difference may be HSP's hereditary nature versus the explicitly non-hereditary nature of spastic diplegia (however, unlike spastic diplegia and other forms of spastic cerebral palsy, HSP cannot be reliably treated with selective dorsal rhizotomy).

Ultimate confirmation of HSP diagnosis can only be provided by carrying out genetic tests targeted towards known genetic mutations.

Classification

Hereditary spastic paraplegias can be classified based on the symptoms; mode of inheritance; the patient’s age at onset; the affected genes; and biochemical pathways involved.

Treatment

No specific treatment is known that would prevent, slow, or reverse HSP. Available therapies mainly consist of symptomatic medical management and promoting physical and emotional well-being. Therapeutics offered to HSP patients include:

  • Baclofen – a voluntary muscle relaxant to relax muscles and reduce tone. This can be administered orally or intrathecally. (Studies in HSP [21][22][23])
  • Tizanidine – to treat nocturnal or intermittent spasms (studies available [24][25])
  • Diazepam and clonazepam – to decrease intensity of spasms
  • Oxybutynin chloride – an involuntary muscle relaxant and spasmolytic agent, used to reduce spasticity of the bladder in patients with bladder control problems
  • Tolterodine tartate – an involuntary muscle relaxant and spasmolytic agent, used to reduce spasticity of the bladder in patients with bladder control problems
  • Botulinum toxin – to reduce muscle overactivity (existing studies for HSP patients[26][27])
  • Antidepressants (such as selective serotonin re-uptake inhibitors, tricyclic antidepressants and monoamine oxidase inhibitors) – for patients experiencing clinical depression
  • Physical therapy – to restore and maintain the ability to move; to reduce muscle tone; to maintain or improve range of motion and mobility; to increase strength and coordination; to prevent complications, such as frozen joints, contractures, or bedsores.

Prognosis

Although HSP is a progressive condition, the prognosis for individuals with HSP varies greatly. It primarily affects the legs although there can be some upperbody involvement in some individuals. Some cases are seriously disabling while others are less disabling and are compatible with a productive and full life. The majority of individuals with HSP have a normal life expectancy.[13]

Epidemiology

Worldwide, the prevalence of all hereditary spastic paraplegias combined is estimated to be 2 to 6 in 100,000 people.[28] A Norwegian study of more than 2.5 million people published in March 2009 has found an HSP prevalence rate of 7.4/100,000 of population – a higher rate, but in the same range as previous studies. No differences in rate relating to gender were found, and average age at onset was 24 years.[29] In the United States, Hereditary Spastic Paraplegia is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health which means that the disorder affects less than 200,000 people in the US population.[28]

References

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  2. ^ Depienne, Christel; Stevanin, Giovanni; Brice, Alexis; Durr, Alexandra (2007-12-01). "Hereditary spastic paraplegias: an update". Current Opinion in Neurology. 20 (6): 674–680. doi:10.1097/WCO.0b013e3282f190ba. ISSN 1350-7540. PMID 17992088.
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  14. ^ a b c Schüle, Rebecca; Wiethoff, Sarah; Martus, Peter; Karle, Kathrin N.; Otto, Susanne; Klebe, Stephan; Klimpe, Sven; Gallenmüller, Constanze; Kurzwelly, Delia (2016-04-01). "Hereditary spastic paraplegia: Clinicogenetic lessons from 608 patients". Annals of Neurology. 79 (4): 646–658. doi:10.1002/ana.24611. ISSN 1531-8249.
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  18. ^ Wharton SB, McDermott CJ, Grierson AJ, Wood JD, Gelsthorpe C, Ince PG, Shaw PJ (2003) The cellular and molecular pathology of the motor system in hereditary spastic paraparesis due to mutation of the spastin gene. J Neuropathol Exp Neurol 62:1166–1177
  19. ^ a b c Noreau, A., Dion, P.A. & Rouleau, G.A., 2014. Molecular aspects of hereditary spastic paraplegia. Experimental Cell Research, 325(1), pp.18–26
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  22. ^ Heetla HW, Halbertsma JP, Dekker R, Staal MJ, van Laar T. Improved Gait Performance in a Patient With Hereditary Spastic Paraplegia After a Continuous Intrathecal Baclofen Test Infusion and Subsequent Pump Implantation: A Case Report. Archives of Physical Medicine and Rehabilitation. 2015;96(6):1166-9.
  23. ^ Klebe S, Stolze H, Kopper F, Lorenz D, Wenzelburger R, Deuschl G, et al. Objective assessment of gait after intrathecal baclofen in hereditary spastic paraplegia. Journal of neurology. 2005;252(8):991-3.
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  25. ^ Bes A, Eyssette M, Pierrot-Deseilligny E, Rohmer F, Warter JM. A multi-centre, double-blind trial of tizanidine, a new antispastic agent, in spasticity associated with hemiplegia. Current Medical Research and Opinion. 1988;10(10):709-18.
  26. ^ Hecht MJ, Stolze H, Auf Dem Brinke M, Giess R, Treig T, Winterholler M, et al. Botulinum neurotoxin type A injections reduce spasticity in mild to moderate hereditary spastic paraplegia— Report of 19 cases. Movement Disorders. 2008;23(2):228-33.
  27. ^ de Niet M, de Bot ST, van de Warrenburg BP, Weerdesteyn V, Geurts AC. Functional effects of botulinum toxin type-A treatment and subsequent stretching of spastic calf muscles: A study in patients with hereditary spastic paraplegia. Journal of rehabilitation medicine. 2015;47(2):147-53.
  28. ^ a b National Institute of Health (2008). "Hereditary Spastic Paraplegia Information Page". Retrieved 2008-04-30.
  29. ^ Erichsen, AK; Koht, J; Stray-Pedersen, A; Abdelnoor, M; Tallaksen, CM (June 2009). "Prevalence of hereditary ataxia and spastic paraplegia in southeast Norway: a population-based study" (PDF). Brain. 132 (Pt 6): 1577–88. doi:10.1093/brain/awp056. PMID 19339254.

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