Clinical and Genetic Characterization of a Patient With EED ‐Related Overgrowth Syndrome

Cohen–Gibson syndrome (COGIS) is a rare genetic disorder caused by heterozygous pathogenic variants in EED . As the COGIS phenotypic spectrum remains incompletely characterized, additional cases help refine understanding of the condition. We evaluated a 37‐year‐old man with EED ‐related COGIS features, including overgrowth and intellectual disability. Genetic workup included karyotyping, FMR1 CGG‐repeat expansion testing, whole‐exome sequencing, and a familial segregation analysis, which identified the previously reported heterozygous pathogenic variant NM_003797.5:c.772C>T:p.His258Tyr. Clinical findings and medical history were recorded; birth parameters were obtained retrospectively from parental report due to lack of official documentation. Echocardiography revealed mild mitral valve regurgitation, alongside features uncommon in previously reported patients—normal adult weight, a long face, normal head circumference, normally spaced eyes, camptodactyly, no history of cryptorchidism, and a normal gait. Notably, the patient's father carried the same variant with reduced Sanger peak height, suggesting possible mosaicism. This case highlights potential phenotypic variability in COGIS, including the cardiac finding warranting further study, and underscores the implications of suspected paternal mosaicism for genetic counseling. Further quantitative assessment of mosaicism and cardiac evaluation in future studies could help better define the clinical spectrum of COGIS.