Spastic Ataxia 6, Charlevoix-Saguenay Type

Clinical Characteristics

Ocular Features:

Patches of myelinated axons from retinal neurons in the retina are not unusual in the general population but are especially prominent among families in Canada with SPAX6. These typically appear as striated white or yellowish-white patches with 'fuzzy' borders in the nerve fiber layer of the retina and radiate from the disc. These findings are usually of no functional significance but if sufficiently large and dense can be demonstrated on perimetry as small scotomas. OCT studies in two Belgian families have revealed increased thickness of the peri-papillary retinal nerve fiber layer in both patients and carriers without clinical evidence of myelination. In addition the retinal nerve fiber layer has been described as 'hypertrophied' outside the areas of myelination. Horizontal gaze nystagmus and deficits in conjugate pursuit movements are often present.

Systemic Features:

This neurodegenerative disorder begins in early childhood (12-18 months) with signs of cerebellar ataxia, pyramidal signs, and peripheral neuropathy. Slightly older children develop a mixed-sensorimotor peripheral neuropathy. Dysarthria, limb spasticity, distal muscle wasting, and mitral valve prolapse are often present. Knee reflexes are exaggerated while ankle reflexes are often absent. Extensor plantar responses are usually present. The EMG can show signs of denervation with slowed conduction while brain neuroimaging demonstrates regional atrophy in the cerebellum, especially the superior vermis. Most patients eventually become wheelchair-bound. However, cognitive and daily living skills are preserved into adulthood. Most patients live into the sixth decade.

Genetics

Homozygous or compound heterozygous mutations in the SACS [1] gene (13q12.12) are responsible for this autosomal recessive disorder.

The largest number of cases is found in the Charlevoix-Saguenay region of Quebec, Canada among the descendents of a founder but families have also been found in Asia and Europe.

Treatment

Treatment Options:

No treatment for the general disease is available but specific therapies for some functions such as urinary urgency are available. Physical and speech therapy as well as special education assistance can be helpful for adaptation.

References

Article Title:

Retinal nerve fiber layer thickening in ARSACS carriers [2]

van Lint M, Hoornaert K, Ten Tusscher MP. Retinal nerve fiber layer thickening in ARSACS carriers. J Neurol Sci. 2016 Nov 15;370:119-122.

PubMed ID:

27772739

Finding of retinal nerve fiber layer hypertrophy in ataxia of Charlevoix-Saguenay patients [3]

Garcia-Martin E, Bambo MP, Gazulla J, Larrosa JM, Polo V, Fuertes MI, Fuentes JL, Ferreras A, Pablo LE. Finding of retinal nerve fiber layer hypertrophy in ataxia of Charlevoix-Saguenay patients. Arch Soc Esp Oftalmol. 2013 Apr 3. [Epub ahead of print] English, Spanish.

PubMed ID:

24269465

ARSACS, a spastic ataxia common in northeastern Qu√©bec, is caused by mutations in a new gene encoding an 11.5-kb ORF [4]

Engert JC, B?(c)rub?(c) P, Mercier J, Dor?(c) C, Lepage P, Ge B, Bouchard JP, Mathieu J, Melan?sson SB, Schalling M, Lander ES, Morgan K, Hudson TJ, Richter A. ARSACS, a spastic ataxia common in northeastern Qu?(c)bec, is caused by mutations in a new gene encoding an 11.5-kb ORF. Nat Genet. 2000 Feb;24(2):120-5.

PubMed ID:

10655055

Location score and haplotype analyses of the locus for autosomal recessive spastic ataxia of Charlevoix-Saguenay, in chromosome region 13q11 [5]

Richter A, Rioux JD, Bouchard JP, Mercier J, Mathieu J, Ge B, Poirier J, Julien D, Gyapay G, Weissenbach J, Hudson TJ, Melan?sson SB, Morgan K. Location score and haplotype analyses of the locus for autosomal recessive spastic ataxia of Charlevoix-Saguenay, in chromosome region 13q11. Am J Hum Genet. 1999 Mar;64(3):768-75. Erratum in: Am J Hum Genet 1999 Apr;64(4):1257.

PubMed ID:

10053011