Down's syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. Down syndrome is by far the most common and best known chromosomal disorder in humans and the most common cause of intellectual disability. The extra chromosome 21 affects almost every organ system and results in a wide spectrum of phenotypic consequences. These include life-threatening complications, clinically significant alteration of life course and dysmorphic physical features.
Down syndrome is the most common autosomal abnormality. The frequency is about 1 case in 800 live births. Each year, approximately 6000 children are born with Down syndrome. About 92% of pregnancies in Europe with a diagnosis of Down syndrome are terminated. Affected neonates tend to be placid, rarely cry, and have hypotonia. Most have a flat facial profile, although some appear normal at birth and then develop characteristic facial features during infancy. A flattened occiput, microcephaly, and extra skin around the back of the neck are common.
The underlying disorder cannot be treated. Management depends on specific manifestations. Some congenital cardiac anomalies are repaired surgically. Hypothyroidism is treated with thyroid hormone replacement. Care should also include genetic counseling for the family, social support. Most research into Down syndrome has focused on understanding the mechanisms behind its symptoms. In XIST chromosome therapy The UMMS team has reported initial success in silencing the additional chromosome in pluripotent stem cells donated by a patient with Down syndrome. They achieved this by inserting an RNA gene into the additional copy of chromosome 21. This gene, called XIST, plays a role in turning off one of the two X chromosomes in female mammals, and the UMMS researchers found that it was effective at repressing the genes across the extra chromosome in their laboratory stem cells.