Down syndrome, general aspects

By Cristiano Antonino On Dec 9, 2022

Down Syndrome is a genetic condition characterised by the presence of an extra chromosome in the cells: instead of 46 chromosomes in the nucleus of each cell there are 47, i.e. there is an extra Chromosome No. 21; hence also the term Trisomy 21

Genetic does not mean hereditary, in fact in 98% of cases Down Syndrome is not hereditary

This chromosomal alteration affects both sexes and all racial groups.

The consequence of this alteration is a handicap, characterised by a delay in the child’s mental, physical and motor development.

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Epidemiology of Down syndrome

Currently, 1 in every 1,200 children in Italy is born with this condition.

Thanks to the development of medicine and increased care for Down’s syndrome sufferers, their life span has lengthened so much that we can now speak of a life expectancy of 62 years, which is destined to grow further in the future.

An estimated 38,000 people with Down’s syndrome live in Italy today.

The causes are still unknown

Numerous epidemiological investigations have shown, however, that the incidence increases with increasing maternal age, particularly after the age of 35. This does not rule out the possibility that children with Down’s syndrome are also born to younger women, but an older woman is more likely.

The other proven risk factor is having had a previous child with the syndrome.

Genetic aspects of Down syndrome

There are three types of chromosomal abnormalities, all characterised by a supernumerary chromosome 21:

Complete Free Trisomy 21 (95% of cases) is the most frequent abnormality and is characterised by the presence of three chromosomes 21 instead of two in all the body’s cells;

In free Trisomy 21 in mosaicism (2% of cases) some cells are normal with 46 chromosomes others with 47, resulting in slight phenotypic changes;

In translocation trisomy 21 (3% of cases), the extra chromosome 21 is not free but migrates to another chromosome, making no change to the total number of chromosomes, which remains at 46.

An important examination that makes it possible to detect chromosome alterations in the foetus is AMNIOCENTESIS.

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