Congenital cerebellar ataxias
Congenital ataxic syndromes are rare and probably underdiagnosed. Clinical presentation is often non-specific, with motor and mental retardation, sometimes associated with spasticity and microcephaly. Nystagmus and intention tremor can be observed before ataxia becomes evident. Ataxia is usually not progressive and improvement has been observed in some cases during the course of the disease. Many individuals with cerebellum agenesis never develop symptoms of cerebellar dysfunction. Inheritance is autosomal recessive in most cases, but dominant and Xlinked transmission has also been reported. Sporadic cases are often misdiagnosed as cerebral palsy. Ataxia is present in 15% of the patients with cerebral palsy and a large proportion of those with no history of perinatal asphyxia may have a genetic disorder.
Granule cell layer hypoplasia (OMIM 213200)
This is an autosomal recessive, congenital cerebellar ataxia also characterized by mental deficiency and delayed motor milestones. The disorder is not progressive and long survival has been described. The cerebellum is small, with severe loss of granule cells and heterotopic Purkinje cells.
Two forms of autosomal recessive pontocerebellar hypoplasia have been described. Type 1 is associated with neuromuscular weakness, hypoventilation, and death during the first year of life. Type 2 (OMIM 277470) is characterized by microcephaly, severely impaired mental and motor development, chorea or dystonia, and seizures. Some patients die during childhood, but survival to adulthood is possible. In the latter form, computed tomography (CT) scan and magnetic resonance imaging (MRI) show marked hypoplasia of the pons, the vermis, and the cerebellar hemispheres, and progressive cerebral atrophy.