Joubert's syndrome commonly presents with which feature?

• A. Severe muscle hypertrophy
• B. Hypotonia
• C. Hearing loss
• D. Visual field loss

Answer: (B)

Joubert syndrome is typically marked early by low muscle tone because the hindbrain, especially the cerebellar vermis and brainstem, isn’t developing normally. This disruption affects the neural signals that help keep muscles toned and coordinated, so infants present as hypotonic, with delayed motor milestones. As development progresses, coordination problems and ataxia become more evident, and other features like abnormal eye movements or breathing abnormalities can appear. Among the given options, hypotonia best fits the usual early presentation. The other features aren’t characteristic of Joubert syndrome: severe muscle hypertrophy isn’t typical and doesn’t reflect the nervous-system–driven tone deficit; while hearing loss or visual field loss can occur in various conditions, they are not defining or common early features of Joubert syndrome.