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Spinocerebellar Degenerations

Timothy C. Hain, MD Page last modified: January 16, 2016

Figure 1: Sagittal MRI of person with an inherited cerebellar degeneration (of unknown origin). This MRI shows prominent atrophy (shrinkage) of the midline (called the vermis).

 

 

 

 

 

 

 

 

The main goal of this page is to serve as a repository for recent information about inherited cerebellar degenerations. It is not comprehensive, but we hope that it might be of some use to individuals searching for information about these rare conditions on the web. We highly recommend also using the OMIM database, which can be accessed on the web. A large number of the genetic ataxias can be tested for using contemporary methodology. An example of a lab that does this is Athena.

Most of the information here concerns inherited conditions, as there is considerable new data derived from researchers using a nearly complete map of the human genome (your tax dollar is doing some good !), and improvements in the technology of molecular biology. It seems quite feasible that within the next decade, we may be able to determine the gene that is damaged in most inherited cerebellar degenerations. As these data become known, it may also be possible to target specific therapies, probably over the next 2 decades. In other words, stay tuned, but we aren't there yet.

There are numerous non-genetic causes of cerebellar disease. which are not covered here.

What to do:

If you have a SCA -- we suggest that you do the following:

DISEASE LISTINGS

Pages on this site outside of this main SCA page. Generally these pages exist to host more specific information (often containing videos) of patients with this diagnosis.

 

SPINOCEREBELLAR ATAXIAS:

All of these disorders exhibit gradually progressive pancerebellar dysfunction, usually beginning in childhood, differentiated by other nervous system involvement.  These disorders were previously known as autosomal dominant cerebellar ataxias. The prevalence of SCA's is estimated to be about 1-4/100,000, but it can be much higher in some regions because of the founder effect. SCA's are all autosomal dominant.

SCA Type findings and comments Mutation
SCA-1 (3-15%) Hypermetric saccades, slow saccades, UMN CAG repeat, 6p
SCA2 (6-15%)

Diminished velocity saccades, areflexia

Common in Cuba.

CAG repeat, 12q
SCA3 (MJD, 30-40%)

Gaze-evoked nystagmus, UMN, slow saccades.

Common in the Azores.

CAG repeat, 14q
SCA-4 (17 families) areflexia Chromosome 16q
SCA-5 Pure cerebellar Chromosome 11
SCA-6

Downbeating nystagmus, positional vertigo

Symptoms can appear for the first time as late as 65 years old.

CAG repeat, 19p (Calcium channel gene)
SCA-7 Macular degeneration, UMN, slow saccades CAG repeat, 3p
SCA-8 Horizontal nystagmus CTG repeat, 13q
SCA-10 (Zu et al, 5 families) ataxia, seizures, primarily in Mexicans Chromosome 22q linked, pentanucleotide repeat
SCA-11   15q
SCA-12 (rare, OHearn et al) Head and hand tremor, akinseia 5q CAG
SCA-13 (rare) Mental retardation 19q
SCA-14 (rare) Myoclonus 19q
SCA-15/16/29 Head and hand tremor 8q
SCA17 Age of onset 20-60, dystonia, chorea, spasticity, dementia  
SCA18 Age of onset 12-25, neuropathy, muscle weakness, atrophy, fasculations, pyramidal signs.  
SCA 19/22 Mild cerebellar syndrome, dysarthria  
SCA20 Age of onset 30-40, presents with dysarthria, palatal tremor  
SCA21 Age of onset 6-30, mild cognitive, tremor, akinesia, rigidity  
SCA22 -- see sca19    
SCA23 40-60, pyramidal tract, sensory loss  
SCA24 -- not listed.    
SCA 25 ataxia with sensory neuropathy, vomiting and gastrointestinal pain. 2p
SCA34 Oculomotor, resembles PSP ELOVL4
SCA35 Age of onset 40-48, pyramidal signs, sensory loss, spasmodic torticollus  
SCA36 Age of onset 40-60, tongue and skeletal muscle atrophy and fasiculation, hearing loss. 20p13-12.2/NOP56
SCA37 Pure cerebellar syndrome  
SCA38 Age of onset 40-50, axonal neuropathy, vermal atrophy  
DRPLA

Chorea, seizures, primarily found in Japan

12p CAG expansion

SCA1-3, SCA6-7m 12 and 16, are genetically associated with unstable CAG trinucleotide repeats. Trinucleotide repeats are abnormal "nonsense" areas in human DNA, that tend to get bigger with time. In successive generations, the size of the CAG repeat tends to get bigger causing a decrease in age at onset (called anticipation). Other CAG repeat diseases include Huntington's disease, dentatorubral-pallidoluysian atrophy, and spinal and bulbar muscular atrophy. Surprisingly, the CAG repeats in the SCA1-3 are found on different chromosomes.  Other trinucleotide repeat diseases include myotonic dystrophy and fragile X syndrome. In trinucleotide repeats, an expansion may increase when passed between an affected parent and his or her affected child -- this is called anticipation. The premutation carrier state of Fragile-X is also associated with cerebellar findings (Berry-Kravis et al, 2003). This mutation has a frequency of 1/250 in women and 1/813 men.

In SCA1 there is atrophy of Purkinje cells as well as loss of many afferent projections to cerebellar cortex, atrophy of dentatorubral pathways, the dorsal columns and certain cranial nerve nuclei.. SCA1 maps to chromosome 6p. Saccade amplitude is reportedly increased in SCA1, resulting in hypermetria (Rivaud-Pechoux et al, 1998). In dominant kindreds, Moseley et al (1998) found SCA1 in 5.6%.

SCA2 is associated with marked loss or slowing of saccadic eye movements. There is olivopontocerebellar atrophy. SCA2 maps to chromosome 12q. SCA2 may be the most common of the CAG repeat type autosomal dominant cerebellar ataxias. Saccadic velocity (rapid eye movement velocity) is decreased in SCA2 (Rivaud-Pechoux et al, 1998). In dominant kindreds, Mosely et al found SCA2 in 15.2%.

SCA3, which is dominantly inherited, is also known as Machado-Joseph disease. We have some case examples of this disorder here.

SCA6 is an autosomal dominant ataxia associated with small expansions of a trinucleotide repeat (CAG) in the gene CACNL1A4, which encodes a voltage-gated calcium channel. Zoghbi (1997) reviews the genetics of this disorder.

Patients with SCA6 can have at least three different syndromes: episodic ataxia, cerebellar ataxia plus brainstem or long tract degeneration, or pure cerebellar ataxia. Calcium channels are identified in Purkinje and granule neurons. Clinically they have a coarse gaze-evoked nystagmus, downbeat nystagmus on lateral gaze, and poor visual suppression (Gomez et al, 1997). SCA6 accounts for about 30% of dominant ataxias in Japan, and between 5-15% of dominantly inherited ataxia in the United States (Geshwind et al, 1997; Mosely et al, 1998). Imaging studies reveal cerebellar atrophy with relative sparing of the brainstem. In Japan, ataxia is the most common initial symptom. Patients with prolonged courses exhibit dystonic postures, involuntary movements and abnormalities in tendon reflexes (Ikeuchi et al, 1997). Takeichi et al (2000) reported that while ocular smooth pursuit is diminished, vestibular cancellation is normal. This may be a distinctive finding of this condition. As mentioned above, patients with calcium channelopathies including SCA-6 and EA2 have deficient ocular responses to otolith input.

SCA7, also dominantly inherited,  is associated with retinopathy or blindness. It is also a CAG repeat disorder. Mosely et al (1998) found SCA7 in about 5% of dominantly inherited ataxias. We illustrate a case of this here.

SCA8 was described in 2000 by Ikeda and others. It is a CAG/CTG repeat disorder. It is characterized by incoordination, ataxic dysarthria, impaired smooth pursuit, horizontal nystagmus, and atrophy of the cerebellar vermis and hemispheres. Myotonic dystrophy is another CTG repeat disorder. Both show maternal anticipation. Average age of onset is 53.8 years.

According to Matsuura et al, SCA 9 is reserved for disorders yet to be described in the literature, and SCA10 (Zu et al, 1998), designates another autosomal dominant ataxia, with occasional seizures.

SCA-10 is rare in populations other than Mexicans (Matsuura and others, 2002).

SCA-17 is an autosomal dominant cerebellar ataxia caused by CAG repeat expansion in the TATA-box binding protein gene. The clinical features include ataxia, dementia, hyperreflexia, parkinsonism manifestations such as bradykinesia, and postural reflex disturbances.

SCA-34 is autosomal dominant cerebellar ataxia due to an ELOVL4 mutation. Mutations of ELOV4 have been reported in 2 Japanese kindreds and a French-Canadian family. In the Japanese variant, the disorder resembles PSP including the "hot cross bun" sign in some and pontine linear hyperdensities in others. (Ozaki et al, 2015).

SCA-38 is due to a missense mutation of ELOVL5. ELOV5 is involved in fatty acid synthesis. (Di Gregorio et al, 2014).

There are many other ataxias which are not included in the "SCA#" nomenclature.

Grewal and others (1998) described an autosomal dominant spinocerebellar disorder in individuals of mexican-american heritage. The clinical picture included cerebellar ataxia, gaze and rebound nystagmus.

Matsuura et al (1999) mapped an autosomal dominant spinocerebellar ataxia with seizures, also in a hispanic family.

Swartz and others (2003) described an autosomal recessive ataxia with progressive ataxia, corticospinal signs, axonal sensorimotor neuropathy, and disruption of visual fixation by saccadic intrusions. This disorder was mapped to a mutation on 1p36.

References for SCA

Dentatorubral and pallidoluysian atrophy (DRPLA)

DRPLA maps to chromosome 12p, and a gene designated "atrophin-1". It was first described by Smith in 1958 (Neurology 1958:8:205-209), and remains rare outside of Asia. Young adults and children display progressive chorea, cerebellar ataxia, oculomotor function and dementia. This disorder has an unstable CAG repeat. Purkinje cells are intact, unlike SCA1, but there is degeneration of the cerebellar dentate nucleus.

Autosomal dominant cerebellar ataxia associated with pigmentary macular dystrophy maps to chromosome 3p.

Charlevoix-Saguenay

This obscure autosomal recessive spastic ataxia is caused by mutations in the SACS gene. It was first described in Quebec. French Canadians, like other inbred populations, have more autosomal recessive disorders than the rest of the world. It is characterized by a triad of slowly progressive cerebellar ataxia, lower limb pyramidal tract features, and a sensorimotor neuropathy. There may also be retinal changes, urinary symptoms, progressive cerebellar atrophy, and linear hypointensities in the pons on MRI, considered the hallmark of the disease. (Pilliod et al, 2015)

Treatment for cerebellar disorders

In general,  main stream medicine has very little to offer in treatment for cerebellar disorders. In the overwhelming majority of cases, cerebellar disorders are caused by death of cerebellar neurons.  Medicine has no method of regrowing dead neurons.  Normally, only a few subpopulations of neurons (such as related to smell) regenerate. There are a few instances where genes have been traced that allow regeneration to occur (i.e. for hair cells in birds).  Pursuit of this direction seem promising to us. Stem cell transplants, at the present writing (2010) are wishful thinking.

Some medications are helpful in suppressing overactive neuronal circuits that cause tremor -  examples are the benzodiazepines and baclofen.

Some medications are helpful in reducing or increasing motor symptoms -- examples are dopamine agonists (such as L-dopa), and antagonists (such as haloperidol).

The alternative medicine community (AMC ?) offers a multitude of treatments for incurable disorders.  We don't especially recommend any of these ourselves, but a few interesting ones suggested by patients are below:

WHAT CAN YOU DO TO HELP IF YOU HAVE SPINOCEREBELLAR ATROPHY?

  1. Volunteer or otherwise support efforts to do research or disseminate information about SCA
  2. Consider allowing your brain to be autopsied in the event of your death.
  3. See a neurologist yearly to document your clinical course. Keep careful records.

LINKS:

REFERENCES:

Copyright January 16, 2016 , Timothy C. Hain, M.D. All rights reserved. Last saved on January 16, 2016