Trisomy 16
Trisomy 16 is a chromosomal abnormality in which there are 3 copies of chromosome 16 rather than two.[1] It is the most common trisomy leading to miscarriage and the second most common chromosomal cause of it, closely following X-chromosome monosomy.[2] Like most chromosomal abnormalities, trisomy 16 usually causes miscarriage in the first trimester of pregnancy.
It is not possible for a child to be born alive with an extra copy of this chromosome present in all cells (full trisomy 16).[3] It is possible, however, for a child to be born alive with the mosaic form.[4][5]
Contents
Chromosome 16
Normally humans have 2 copies of chromosome 16, one inherited by each parent. This chromosome represents almost 3% of all DNA in cells.[6]
Screening
During pregnancy, women can be screened by chorionic villus sampling and amniocentesis to detect trisomy 16. This can cause fetal growth retardation.[7]
Full trisomy 16
Full trisomy 16 is incompatible with life and most of the time it results in miscarriage during the first trimester. This occurs when all of the cells in the body contain an extra copy of chromosome 16.[7]
Mosaic trisomy 16
Mosaic trisomy 16, a rare chromosomal disorder, is compatible with life, therefore a baby can be born alive. This happens when only some of the cells in the body contain the extra copy of chromosome 16. Some of the consequences include slow growth before birth.[8]
Prenatal diagnosis
During prenatal diagnosis the levels of trisomy in fetal-placental tissues can be analyzed. These levels can be predictors of outcomes in mosaic trisomy 16 pregnancies. In a study of prenatal diagnosis cases, there were 66% live births with an average 35.7 weeks gestational age. About 45% of them had malformations. The most common malformations were CSD, ASD, and hypospadias.[6] However, trisomy 16 does not always result in anatomical abnormalities.[8]
References
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