Medical Genetics A, Pathophysiology Trisomy 18 severely affects all organ systems. In translocations that result in partial trisomy or in cases of mosaic trisomy 18, clinica expression is less severe and longer survival is usualMedical Genetics A. Pathophysiology Trisomy 18 severely affects all organ systems. In translocations that result in partial trisomy or in cases of mosaic trisomy 18, clinical expression is less severe and longer survival is usual