ELUCIDATING THE MECHANISMS UNDERLYING THE GENETIC BASIS OF EDWARD SYNDROME (TRISOMY 18): A REVIEW OF THE EVIDENCE

Abstract

Edwards syndrome is also termed trisomy 18 syndrome. It is an autosomal chromosomal anomaly that occurs due to the presence of an extra chromosome 18. This anamoly was first observed in 1960 by Edwards and his colleagues. It was observed in a neonate who showed various congenital anomalies along with intellectual impairment. Smith et al. corroborated that the presence of an extra chromosome 18 is one of the causes of Edwards syndrome. Edwards syndrome is the second most frequent autosomal trisomy syndrome after trisomy 21. It is found to be living-born with an observed prevalence . However, it is more frequent since there is a high number of fetal losses or terminated pregnancies in cases diagnosed prenatally. As maternal age advances, the likelihood of having a baby with Edwards syndrome (Trisomy 18) also rises.The risk of repetition for a family who had children with full trisomy is approximately one in 100 cases. Edwards syndrome is observed to pose a vast clinical phenotype. Moreover, it is noticed that they have a very guarded prognosis. More than 130 anomalies of various systems such as heart, lungs, brain, skin, musculoskeletal, immune, etc. including almost all body systems, have been noticed in Edwards syndrome patients. It is found that their anomalies occur due to the presence of three copies of chromosome 18. Despite their extra copy of chromosome, the major chromosome observed is the trisomy of chromosome 18, that is observed to be free trisomy-18, which is related to non-disjunction, specially found in the mother's egg cells. Edwards syndrome is found to occur in almost 90 and 95 out of every 100 fetuses who expired in the embryonic or fetal periods of development. Their mean survival time for live-born children is found to range between 2.5 to 14.5 days . One of the primary features of Edwards syndrome is found to be gestalt dysmorphism. Moreover, it is observed that approximately 90 out of 100 the cases of Edwards syndrome occur with cardiac anomalies. More or less, 90 to 95 out of every 100 children suffering from Edwards syndrome tend to have intellectual impairments. Moreover, their features also include fixed flexion deformity of the limbs accompanying overlapping digits, presence of rocker-bottom feet, anomalies in the genitourinary or gastrointestinal tracts. Almost 90 out of 100 children with Edwards syndrome tend to have heart anomalies. Their mean survival time for live-born children is found to range between 2.5 to 14.5 days. Additionally, their features include fixed deformity of the limbs accompanied by overlapping digits, rocker-bottom feet, genitourinary anomalies, or anomalies of the gastrointestinal tracts. Almost 90 out of 100 children with Edwards syndrome tend to have cardiac anomalies. Moreover, approximately 90 to 95 out of 100  children suffering from Edwards syndrome tend to be intellectually impaired.