March 18 is World Trisomy 18 Awareness Day.
Trisomy 18 syndrome is a disorder of human chromosomes which occurs in approximately 1 in 7,000 live births. Trisomy refers to three copies of a chromosome instead of the normal two. In Trisomy 18 syndrome there is a presence of an extra #18 chromosome. Over 90% of infants with Trisomy 18 have full trisomy. This means that they will have trisomy in all the cells of their body. The remainder of the infants with Trisomy 18 will have Trisomy 18 Mosaicism or Partial Trisomy 18.
Trisomy 18 Mosaicism: a syndrome where an individual has an extra third copy of chromosome 18
in only some of the body's cells. T18m is usually less severe than full Trisomy 18.
Partial Trisomy 18: a syndrome where the individual has an extra third copy of only part of chromosome 18 in the cells of the body. The condition is highly variable depending on how many of the body's cells are involved and how much of the chromosome is involved.
Infants born with Trisomy 18 are usually small in size at birth. Other recognizable features of Trisomy 18 are:
- prominence to the back part of the head
- short eyelid fissures
- small mouth and jaw
- external ear variations
- clenched fist with index finger overlapping the third, and the fifth finger overlapping the fourth
- underdeveloped or altered thumbs
- short sternum (breastbone)
- club feet
- redundant skin at the back of the neck
The major impact of Trisomy 18 is a predisposition to congenital malformations, a high incidence of infant mortality, and motor/developmental disability.
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