Clinical features: People with Down Syndrome have a characteristic facial appearance and as infants have poor muscle tone (hypotonia). A clinical diagnosis should be confirmed by chromosome analysis. Learning disabilities range from moderate to severe. A number of important medical complications are associated with Down Syndrome. Congenital heart disease is seen in 40% of people with Down Syndrome, 5% have duodenal atresia or Hirschsprung disease, 2% develop cataracts, 3% have hypothyroidism and 1% go on to develop leukaemia. Alzheimer disease is common after 40 years of age. Increasingly, the diagnosis is made during pregnancy following antenatal screening tests and either chorionic villus sampling (CVS) or amniocentesis. Down syndrome individuals who show mosaicism for both normal and trisomy 21 cells, tend to have milder clinical features than in the full Down syndrome.
Incidence: The overall birth incidence is 1 in 700 live births, with a maternal age effect.
Chromosome result: Down Syndrome is a chromosomal condition related to chromosome 21. Trisomy 21 occurs in 95% of cases, a translocation involving chromosome 21 accounts for 4% and mosaicism for 1% of cases.
Recurrence risk: The empiric recurrence risk to a couple who have had one child with regular trisomy 21 (confirmed on chromosomal analysis) is 1 in 100 of having another child with any chromosome abnormality. Over the age of 35 their risk is about twice the normal maternal age-specific risk. (See Maternal age for table of age specific risks.) Where there is a family history of Down syndrome, the most valuable information in calculating risks for other family members is the karyotype of the affected person. The risk would be that associated with maternal age, if the affected family member had regular trisomy 21. A translocation (which is associated with high risks), should be considered when there is more than one affected member. Appropriate members of the family should then be offered chromosome analysis.
UK Support Group: Down's Syndrome Association Langdon Down Centre 2a Langdon Park Teddington TW11 9PS Tel: 0845 230 0372 Fax: 0845 230 0373 Email: info@downs-syndrome.org.uk
If you would like further information on Down Syndrome please go to either:-
The Least You Need to Know Coffee Break Summary Pitfalls to Avoid Find Out More Clinical Scenarios at Genepool - Down syndrome
Back to genetic conditions index
