Indian J Pediatr 1986; 53 : 761-773 Genetic aspects of congenital cerebellar ataxia D. Kumar Centre for Httman Genetics, Sh~ff~eM Children's Hospital, Universi o" c~/"Sheffield, England Congenital cerebellar ataxia comprises a heterogeneous group of birth defects involving brain stem and cerebellum, characterised by ataxia, spasticity, ehoreoathetotd movements and mental retardation. Three children with congenital cerebellar malformations are described. The presenting features were benign enlargement of head, myoclonie jerks, episodes of hy- pernoia, nystagmus, ataxia, motor delay and mental retardation. Computerised tomography revealed Dandy-Walker cyst in one case and in two cases cerebellar vermis agenesis was associated with a variable degree o f brain stern involvement. Retinal dysplasia and post-axial polydactyly were associated abnormalities in one ease as reported in Joubert's syndrome, an autosomal recessive type of familial cerebellar vermts dysgenesis. Genette factors in the pathogenesis of congenital cerebellar ataxia are reviewed. The relevance o f computerised tomography, electroretinography and prenatal diagnosis by fetal ultrasound is discussed. Genetic counselling in congenital cerebellar ataxia presenting in the first year at" life is important because of the high risk of recnrrence. Key words : Cerebellar ataxia; recessive cerebellar vermis agenesis; Joubert's syndrome; cerebellar hypoplasia; cerebral palsy; Dandy--Walker syndrome; retinal dysplasia; Leber's amaurosis; oral-facial-digital syndrome; polydactyly; computerised tomography; electroretinography; prenatal diagnosis; genetic counselling. Congenital cerebellar ataxia includes a heterogeneous group of birth defects involving the brain stern and cerebellum characterised by episodes of tachypnea, abnormal eye movements, ataxia, spasti- city, choreoathetoid movements and mental retardation. Nosologic delineation of congenital eerebellar ataxia is difficult because the majority of patients have a nonspecific syndrome of ataxia with or without mental retardation and mild Reprint requests:Dr. D. Kumar, Centre for Human Genetics, Sheffield Children's Hospital, Sub- Department of Medical Genetics, University of Sheffield, 117 Manchester Road, Sheffield, S10 5DN, England. 761 spasticity. Some distinctive pathological and clinical syndromes have been delinea- ted on an arbitrary basis. I The disorders which are included under the title of 'hereditary congenital ataxia 'are geneti- cally determined, giving rise to a conge- nital non-progressive syndrome in which ataxia is the most prominent component. The exact incidence of genetic congenital ataxia syndromes is difficult to identify since sporadic cases outnumber familial ones and are often labelled as ataxic or choreoathetoid forms of cerebral palsy. A significant number of cases of ataxic cerebral palsy have been suggested as examples of autosomal recessive con-