The hereditary cerebellar ataxias are a group of degenerative progressive diseases with heterogenous clinical and genetic features, characterized by disorder of motor coordination, gait, posture, speech articulation and oculomotory movements. The degenerative process can be limited to the cerebellum or may involve other structures of the central and peripheral nervous system. The moleuclar defects and the underlying pathogenic mechanisms have not been extensively characterized yet.
In dominant forms, (ADCA), the prevalence has been estimated between 0.8 and 3.5:100,000. The onset is usually between 30 and 50 years of age although some cases presenting childhood or late onset (>60 y.o.) have been reported. Molecular diagnosis is achieved in 50% of ADCA cases and it remains a challeng since more than 36 loci are involved.
Most of the causative mutations are triplets expansion which are responsible for the variability in the age of onset. More recently, point mutations or microdeletions have also been described.
The autosomal recessive cerebellar ataxias (ARCA) as well as X-linked forms, show a prevalence of 7 per 100,000 and involve both the peripheral and central nervous system. Other systems and organs may be also striked. The onset is early, before the age of 20. We distinguish 4 main types of ARCA on the basis of the pathogenetic mechanism: congenital ataxias (developmental defects), progressive degenerative ataxias, ataxias associated with metabolic diseases, ataxias related to defects in DNA repair. The most common forms of ARCA in the Caucasian population are Friedreich’s ataxia and ataxia-telangiectasia.