0 the most common form of Down's syndrome (= a genetic condition associated with learning difficulties in which a person is born with an extra chromosome) that is caused by there being an extra copy of the chromosome number 21 in the body's cells:
In the past year I have identified two cases of trisomy 21 in our screening district.
The proportion of cases of trisomy 21 diagnosed cytogenetically before birth rose.
This Trisomy 21 diagnosis – Down syndrome, in lay terms – was followed not by smiles and "Congratulations! You just had a baby" joy, but by downcast eyes and pity.
