Background Information

Down syndrome is among the commonly occurring genetic diseases and is mainly characterized by mental retardation and conditions such as tissue dimorphism, metabolic disorders, and internal organ abnormalities. The disorder is most prevalent in newborn babies, occurring in 1:700 infants. The main causal agent for DS is nondisjunction. Nondisjunction is caused by an error in the division of cells, which leads to the existence of three copies of chromosome 21 in the embryo (trisomy 21). Consequently, the disorder can also be caused by the presence of the ring chromosome or isochromosome and through Robertsonian translocation (Asim et al., 2015). Isochromosome condition is when two long chromosome arms jointly separate rather than the usual short and long joint separation during the sperm-egg development, leading to trisomy 21 (karyotype 47 XX + 21-females and 47 XX + 21-males). This occurs when there is a failure in the separation of chromosome 21 in the development process of either sperms or eggs cells. On the other hand, Robertsonian translocation is the least cause of DS and occurs when the chromosome’s long arm is linked to a different chromosome, especially chromosome 14. Consequently, Robertsonian translocation can also occur through the attachment of 2 chromosomes 21 and it can be inherited from carrier parents (Kadakol et al., 2019). Robertsonian translocation is known to comprise hereditary factors and 1/3 of its occurrence is inherited. Therefore, all the three causes of DS are as a result of genetic conditions, with only 1% of the cases depicting hereditary factors. Incidences of its occurrence increase with maternal age, however, since younger women possess a higher fertility rate, the chances of giving birth to a DS affected child increases with the mother’s age.