Isolated Duane retraction syndrome
Isolated Duane retraction syndrome is an eye movement disorder that limits the ability to move the eye outward and sometimes inward, often causing the eyeball to pull back into its socket.
Overview
Isolated Duane retraction syndrome is a condition where the eye cannot move outward toward the ear, and sometimes inward toward the nose. As the eye moves inward, the eyeball retracts (pulls back) into the socket, and the eyelid opening narrows. Because of these limitations, the eyes often do not look in the same direction (strabismus), and affected individuals may turn their head to track objects.
Key Features
- Usually affects only one eye (most commonly the left).
- Approximately 10 percent of affected individuals develop amblyopia ("lazy eye").
- There are three types (I, II, and III), differentiated by which eye movements are most severely restricted.
- About 70 percent of cases are isolated, occurring without other physical symptoms.
Causes
In most cases, the cause is unknown. However, some individuals have variants in the CHN1 gene. This gene provides instructions for making the protein N-chimaerin, which is critical for the development of nerves that control the muscles surrounding the eyes (extraocular muscles). Variants in this gene disrupt the development of these nerves, preventing effective control of eye movement.
Inheritance
Most cases are simplex, occurring in people with no family history of the disorder. When the condition is familial, it typically follows an autosomal dominant pattern of inheritance, where one copy of the altered gene is sufficient to cause the disorder.