The complex clinical and genetic classification of inherited ataxias. II. Autosomal recessive ataxias.
Autosomal recessive ataxias are a heterogeneous group of rare neurodegenerative diseases characterized by early onset cerebellar ataxia associated with various neurologic, ophthalmologic and systemic signs. In comparison with autosomal dominant ataxias, the group of recessive ataxias is less extensively characterized. In fact, only a few conditions have been genetically characterized. The pathogenesis of these forms is associated with a "loss of function" of specific cellular proteins involved in metabolic homeostasis, cell cycle, and DNA repair/protection processing. The two most common autosomal recessive ataxias, in European countries, are Friedreich's ataxia and ataxia telangiectasia. Other forms are much less frequent, and include ataxia with vitamin E deficiency, abetalipoproteinemia. Refsum's disease, spastic ataxia, infantile onset spinocerebellar ataxia, and ataxia with oculomotor apraxia. These pathological conditions, although extremely rare, have nevertheless to be carefully considered in differential diagnosis, not only for correct nosographical classification, but particularly, for specific prognostic and therapeutic implications. Some of these diseases exhibit a peculiar regional distribution. An updated review of the clinical, genetic, and pathogenic aspects of recessive ataxias is presented. Specific management problems with respect to diagnosis and genetic counseling are discussed.