Hypotonia is particularly evident in the neonatal period (the period immediately after birth) and during infancy. Children may be moderately or severely affected and may lack head control, have difficulties rolling over, sitting, standing and walking. Unsteadiness due to ataxia and balance problems may also be present. Joubert syndrome also affects breathing and abnormal over breathing commonly occurs during the neonatal period. This may improve with age but, in some cases, it persists and may threaten survival.
Individuals with Joubert syndrome have abnormal eye movements including a squint with or without retinal degeneration, and with or without congenital blindness (see entry Vision disorders in Childhood). Young infants with Joubert syndrome often have a characteristic appearance with a large head, prominent forehead, high rounded eyebrows, broad nasal ridge, mild epicanthus, upturned nose with evident nostrils, open mouth and protruding tongue. This appearance becomes less pronounced as the child grows.
Cognitive and physical development is delayed in Joubert syndrome. Moderate-to-severe learning difficulties are common, language may be delayed. Some children with Joubert syndrome are hyperactive, combative and difficult to manage whilst others display normal behaviour.