![]() The reason behind this difference in the prevalence of different types of CHD in different regions is still unclear, and many factors such as regional proximity have been found to contribute. There is geographical variation in the prevalence of the cardiac defect in Down syndrome, with VSD being the most common in Asia and secundum type ASD in Latin America. The other cardiac defects associated with trisomy 21 are secundum atrial defect (10%), tetralogy of Fallot (6%), and isolated PDA (4%), while about 30% of the patients have more than one cardiac defect. Together with AVSD, these account for more than 50% of congenital cardiac defects in patients with Down syndrome. ![]() It is said to be associated with the mutation of the non-Hsa21 CRELD1 gene The second most common cardiac defect in Down syndrome is a ventricular septal defect (VSD), which is seen in about 32% of the patients with Down syndrome. The most common cardiac defect associated with Down syndrome is an atrioventricular septal defect (AVSD), and this defect makes up to 40% of the congenital cardiac defects in Down syndrome. The incidence of CHD in babies born with Down syndrome is up to 50%. Though different suggestions have been made about the geographical as well as seasonal variation in the occurrence of different types of congenital cardiac defects in trisomy 21, so far none of the results have been conclusive. Ĭongenital cardiac defects are by far the most common and leading cause associated with morbidity and mortality in the patients with Down syndrome especially in the first 2 years of life. These patients have a wide array of signs and symptoms like intellectual and developmental disabilities or neurological features, congenital heart defects, gastrointestinal (GI) abnormalities, characteristic facial features, and abnormalities. ĭifferent clinical conditions are associated with Down syndrome as different systems are affected by it. After a thorough study of different analyses, it became clear that a single critical region gene cannot cause all the phenotypical features associated with trisomy 21, rather it is more evident that multiple critical regions or critical genes have a role to play in this phenomenon. DSCR on 21q21.22 is responsible for many clinical features of Down syndrome. Down syndrome critical regions (DSCR) are few chromosomal regions which are associated with partial trisomy for Has21. Ĭritical region hypothesis is also well known in this list. ![]() The other popular hypothesis is amplified development instability hypothesis, according to which the genetic imbalance created by a number of trisomic genes and results in a greater impact on the expression and regulation of many genes. It further includes the possibility of association of different genes with different phenotypes of Down syndrome. Among them is gene dosage imbalance in which there is an increased dosage or number of genes of Hsa21, which results in increased gene expansion. There are different hypothesis related to genetic basis of Down syndrome and association of different genotypes with the phenotypes. The majority of patients with Down syndrome have an extra copy of chromosome 21.
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