This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Trisomy 17 mosaicism is a chromosomal abnormality in which there are three copies of chromosome 17 in some cells of the body, rather than the usual two copies. Trisomy 17 mosaicism is one of the rarest trisomies in humans. It is often incorrectly called trisomy 17 (also referred to as full trisomy 17), which is when three copies of chromosome 17 are present in all cells of the body. Full trisomy 17 has never been reported in a living individual in the medical literature. Few cases of trisomy 17 mosaicism have been described, most having been detected during pregnancy through a test called amniocentesis. Only a few individuals have had a confirmed diagnosis of trisomy 17 mosaicism after birth. Because the proportion and location of cells with trisomy 17 differs from case to case, the presence and severity of signs and symptoms may vary significantly from person to person.
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