Once the mutated gene has been identified, both the normal and abnormal gene and its protein product can be studied. The results can assist both the clinician and basic science researcher. Gene mapping and cloning can lead to the development of genetic testing, accurate diagnostic criteria, and phenotype-genotype correlation, and may provide the basis for new strategies for prevention and treatment. Concomitant strabismus occurs when the misalignment or the angle of deviation of the eyes remains constant independent of the direction of gaze and most commonly is felt to result from an upper motor neuron abnormality. Although Hippocrates noted a familial tendency for isolated concomitant strabismus, it does not follow a clear monogenic dominant or recessive pattern of inheritance, and the precise genetics have yet to be fully elucidated.
Concomitant strabismus is, however, a frequent component of genetic syndromes.
It is found in association with chromosomal trisomies and deletions, with some of the trinucleotide repeat expansion disorders, and in association with multisystem disorders. The occurrence of concomitant strabismus as a component of genetic syndromes that map to multiple chromosomal locations reinforces the concept that concomitant strabismus is a phenotype with marked genetic heterogeneity and can result from defects at many genetic locations. Incomitant strabismus occurs when the misalignment or the angle of deviation of the eyes varies with gaze direction. This results from mechanical dysfunction in the orbit or neuromuscular dysfunction at the level of the muscle, nerve, or brainstem. The ophthalmoplegia is virtually complete with the eyes fixed at 20 to 40 degrees below the horizontal.