SNP Shot: Genomic Insights

Isolated Duane retraction syndrome is an eye movement abnormality where the affected eye struggles to move outward (away from the nose). In some instances, inward movement (toward the nose) is also restricted. When attempting to look inward, the eyelid may droop or close partially, and the eyeball retracts into the eye socket. Typically, only one eye is affected. Approximately 10% of individuals with isolated Duane retraction syndrome experience amblyopia, also known as "lazy eye," leading to vision impairment in the affected eye.

Around 70% of Duane retraction syndrome cases are considered isolated, meaning they occur without other associated health problems. However, Duane retraction syndrome can also be a component of broader syndromes impacting other parts of the body. For instance, Duane-radial ray syndrome involves Duane retraction syndrome alongside bone abnormalities in the arms and hands.

Scientists have classified isolated Duane retraction syndrome into three types: I, II, and III. These types differ based on which eye movements are most limited: inward, outward, or both. A common characteristic across all three types is eyeball retraction during inward eye movement.

Inheritance:

Isolated Duane retraction syndrome usually arises spontaneously in individuals with no family history of the condition. These are called simplex cases, and their genetic origin remains unknown. Less frequently, isolated Duane retraction syndrome can be inherited within families. Familial cases typically follow an autosomal dominant inheritance pattern. This implies that a single copy of a mutated gene in each cell is enough to cause the disorder. Isolated Duane retraction syndrome caused by CHN1 gene mutations is also inherited in an autosomal dominant manner.

In rare instances of isolated Duane retraction syndrome, the family history suggests autosomal recessive inheritance. In these families, siblings may be affected, while the parents show no symptoms. Parents of children with an autosomal recessive condition are carriers; they each possess one copy of the mutated gene in their cells. Affected children inherit two copies of the mutated gene, one from each parent. However, the specific gene(s) responsible for autosomal recessive isolated Duane retraction syndrome are yet to be identified.