Abstract
Down syndrome is a congenital genetic disorder caused by abnormalities in the number, structure, or arrangement of chromosome 21 that cause cognitive impairment, congenital malformation, immune disorder, congenital heart disease, and other disorders. It is the most common chromosomal abnormality worldwide. ‘Down syndrome’ is named in honor of John Langdon Heydon Down, who described its clinical manifestations in an article in 1866. Down syndrome is a congenital genetic disorder caused by abnormalities in the number, structure, or arrangement of chromosome 21 that cause cognitive impairment, congenital malformation, immune disorder, congenital heart disease, and other disorders. It is the most common chromosomal abnormality worldwide. ‘Down syndrome’ is named in honor of John Langdon Haydon Down, who described its clinical manifestations in an article in 1866. Down syndrome may result from classic trisomy 21, Robertsonian translocation, or chromosomal mosaicism. Maternal age is the most common risk factor, as pathogenesis is linked to biological ovarian aging. Biological ovarian aging may increase the risk of chromosome 21 nondisjunction through hormonal imbalance, depletion of the oocyte pool, impaired cohesion function, oxidative stress, and altered elimination of aneuploid embryos. Knowledge of risk factors and their etiopathogenesis may help recommend an ideal maternal age for pregnancy. A better understanding of these mechanisms may support genetic counseling, pregnancy planning, and appropriate prenatal screening.