Humans are bilaterally symmetric, but asymmetries occur normally in development and are influenced by both genetic and environmental processes. Disruptions in the left-right patterning can lead to situs defects or diseases that unilaterally affect an area of the body. The exact cause and mechanism through which such unilateral diseases develop is still under investigation, but diseases such as unicoronal craniosynostosis (the premature fusion of the coronal suture on one side of the skull) can help provide insight. Unicoronal synostosis occurs in two forms, right (RUCS) and left (LUCS), in unequal proportions, which suggests that different mechanisms lead to each form. This study uses cranial morphology as an indication of the underlying biological processes to compare the two forms. Landmark locations were marked on computed tomography scans of 19 RUCS, 8 LUCS, and 20 control (unaffected) cases and then analyzed with geometric morphometrics. The data showed that RUCS and LUCS are similarly asymmetric and vary only in the direction of asymmetry; they therefore seem to be the result of similar biological processes. The difference in prevalence may be the result of one side of the head being more prone to synostosis than the other due to factors such as brain growth or mechanical forces. Other unilateral diseases may follow similar trends but need to be further explored.
