[At the crossroads between developmental and degenerative diseases: the cerebellar disorders of early infancy. Classification and practical approach].

The developmental characteristics of the cerebellum, including its histogenesis which persists well beyond birth, explain, at least in part,why the mechanisms of cerebral disorders of infancy remain equivocal. The nosology of certain congenital ataxias, especially those with cerebellar hypoplasia, remains ambiguous, at the crossroads between early degenerative disease and congenital non-progressive anomalies. We have revisited the clinical approach to the most frequent situations: (1) the careful dysmorphology work-up must search for any element of various recognizable syndromes, especially those transmitted by autosomal recessive inheritance. An update of list of such syndromes is provided. (2) Cerebellum imaging must be obtained as early as possible and re-documented with a long-term follow-up. Emerging 3D techniques should help improve morphological evaluation. (3) One the contrary, a complex biochemical work-up, looking for metabolic diseases, is required only when the clinical and radiological evaluations provide unusual data. (4) Mental status is always the most relevant element of prognosis. t is frequently compromised, including in congenital non-progressive ataxia with normal imaging. Beyond the classical strategies, the genetic approach must take into consideration possible phenotypic homologies with natural or experimental animal models. This approach is illustrated by the recent discovery of mutations with the human homolog of the Reeler gene in a subset of cerebellar agenesis associated with other dysgenetic elements.