]> 2026-07-31T07:27:52+00:00 WBR0144 0 en Mosaicism Heteroplasmy Pleiotropy Pleiotropy occurs when one gene influences multiple phenotypic traits. Consequently, a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously. While the ''Fibrillin'' mutations of Marfan syndrome are illustrations of pleiotropy, pleiotropy is not the most accurate descriptor of the resident's argument. Locus heterogeneity Variable expressivity Variable expressivity occurs when a phenotype varies among individuals who have the same genotype. Although MFS is characterized by variable expressivity, whereby some patients patients have dissimilar manifestations, locus heterogeneity better explains the resident's argument in the vignette. Genetics A 37-year-old man presents to the emergency department (ED) for a severe sudden "tearing" chest pain that radiates to his back. The patient is tall, has abnormal laxity of his joints, and long extremities. A medical student suggests that this patient has Marfan syndrome, whereas the resident in the ED contends that long extremities and joint laxity may be features of other inherited conditions. Which of the following mechanism's explains the resident’s argument? D Musculoskeletal/Rheumatology 2020-10-27T23:28:21Z 2459150.4780208 WBR0144