Duane-radial ray syndrome

Duane-radial ray syndrome is a rare disorder that affects the eyes and causes abnormalities of bones in the arms and hands.

Presentation
The name of the condition refers to the two elements which most commonly present:


 * This condition is characterized by a particular problem with eye movement called Duane anomaly (also known as Duane syndrome). Duane anomaly results from the improper development of certain nerves that control eye movement. This condition limits outward eye movement (toward the ear), and in some cases may limit inward eye movement (toward the nose). As the eye moves inward, the eye opening becomes narrower and the eyeball may pull back (retract) into its socket.


 * Bone abnormalities in the hands include malformed or absent thumbs, an extra thumb, or a thumb that looks like a finger. Partial or complete absence of bones in the forearm is also common. Together, these hand and arm abnormalities are called radial ray malformations.

People with the combination of Duane anomaly and radial ray malformations may have a variety of other signs and symptoms. These features include unusually shaped ears, hearing loss, heart and kidney defects, a distinctive facial appearance, an inward- and downward-turning foot (a clubfoot), and fused vertebrae.

Related conditions
The varied signs and symptoms of Duane-radial ray syndrome often overlap with features of other disorders.


 * For example, acro-renal-ocular syndrome is characterized by Duane anomaly and other eye abnormalities, radial ray malformations, and kidney defects. Both conditions can be caused by mutations in the same gene. Based on these similarities, researchers are investigating whether Duane-radial ray syndrome and acro-renal-ocular syndrome are separate disorders or part of a single syndrome with many possible signs and symptoms.


 * The features of Duane-radial ray syndrome also overlap with those of a condition called Holt-Oram syndrome; however, these two disorders are caused by mutations in different genes.

Genetics
Mutations in the SALL4 gene cause Duane-radial ray syndrome. The SALL4 gene is part of a group of genes called the SALL family. These genes provide instructions for making proteins that are involved in the formation of tissues and organs before birth. SALL proteins act as transcription factors, which means they bind to specific regions of DNA and help control the activity of particular genes. Mutations in the SALL4 gene prevent one copy of the gene in each cell from making any protein. It remains unclear how a reduction in the amount of SALL4 protein leads to Duane anomaly, radial ray malformations, and the other features of Duane-radial ray syndrome and similar conditions. Duane-radial ray syndrome often is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.