الفهرس 
Down syndromeOnly 14 pages are availabe for public view
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Abstract
Summary Down syndrome (DS) is the most frequently occurring chromosomal abnormality in humans and affecting between 1 in 400-1500 babies born in different populations, depending on maternal age, and prenatal screening schedules. DS is the most common genetic cause of intellectual disabilities worldwide and large numbers of patients throughout the world encounter various additional health issues, including heart defects, hematopoietic disorders and early-onset Alzheimer disease. The syndrome is due to trisomy of the whole or part of chromosome 21 in all or some cells of the body and the subsequent increase in expression due to gene dosage of the trisomic genes. It is coupled with mental retardation, congenital heart defects, gastrointestinal anomalies, weak neuromuscular tone, dysmorphic features of the head, neck and airways, audiovestibular and visual impairment, characteristic facial and physical features, hematopoietic disorders and a higher incidence of other medical disorders. The incidence of births of children with DS increases with the age of the mother. However, due to higher fertility rates in younger women, the probability of having a child with DS increases with the age of the mother and more than 80% of children with DS are born to women under 35 years of age. Many epidemiological studies interested with the prevalence of DS have been conducted over the last 100 years, describing the multifactorial nature of the syndrome and studying both the genetic