Trisomy 21 (Down syndrome)

People with Down syndrome characteristically have three instead of the normal two chromosomes 21 in all somatic cells.With an occurrence of 1:650 live births, Down syndrome is the most common of the congenital syndromes.Common physical features are eyelids that slant up and out, a single transverse palmar crease (also called the Simian crease), significantly reduced muscle tone and a tendency to have lower than average cognitive ability. There are also often malformations of the inner organs, with the heart being most frequently affected; 40-50 per cent of children with Down syndrome also have a congenital heart defect, which typically affects the cardiac septum. Althoughthe fault is usually a complete AV canal septal defect, there could also be the presence of a ventricular septal defect or an atrial septal defect. Due to excellent treatment methods, in particular for cardiac anomalies, the life expectancy of Europeans with Down syndrome has risen from an average of nine years (1929) to 60 years (2004).