Trisomy 16

Trisomy 16 is a chromosomal abnormality in which a person carries three copies of chromosome 16 instead of the usual two. It is the most common autosomal trisomy found in miscarried pregnancies and the second most common chromosomal cause of miscarriage overall, trailing only monosomy of the X chromosome, and it is present in about six percent of all miscarriages. The abnormality arises from nondisjunction, in which chromosomes fail to separate correctly during the formation of egg or sperm cells, and full trisomy 16 is incompatible with life, almost always ending in early pregnancy loss. A milder mosaic form exists, in which only some of a person's cells carry the extra chromosome, and this form can occasionally result in a live birth with a range of physical anomalies. Diagnosis is typically made through chorionic villus sampling or amniocentesis during pregnancy, within the specialty of medical genetics.