NORD gratefully acknowledges M. Hassan Toufaily, MD, Postdoctoral Research Fellow, Massachusetts General Hospital and Brigham and Women's Hospital, for assistance in the preparation of this report.
Triploidy is a rare chromosomal abnormality. Triploidy is the presence of an additional set of chromosomes in the cell for a total of 69 chromosomes rather than the normal 46 chromosomes per cell. The extra set of chromosomes originates either from the father or the mother during fertilization. Infants with triploidy usually are miscarried early in the pregnancy. If the pregnancy continues to term, the infant dies within the first days of life. A few affected individuals have been reported to have survived to adulthood, but suffered from developmental delay, learning difficulties, seizures, hearing loss and other abnormalities. Those that survive have mosaic triploidy, meaning that some cells have the normal number of 46 chromosomes and other cells have 69 chromosomes per cell. Infants affected with complete triploidy suffer from growth restriction and multiple birth defects.
Infants affected with triploidy suffer from heart defects, abnormal brain development, adrenal and kidney defects (cystic kidneys), spinal cord malformations (neural tube defects) and abnormal facial features (widely spaced eyes, low nasal bridge, low-set malformed ears, small jaw, absent/small eye, and cleft lip and palate). The third and fourth fingers of the hands and the second and third toes of the feet may be united and the hands may have unusual simian creases. There may also be liver and gallbladder defects, twisted intestines and deformities of the fingers and toes. The placenta in triploidy may be immature, large, and filled with cysts. Individuals who are mosaic will survive longer than those with complete triploidy but usually suffer from intellectual disability, developmental delay, depression, seizures, short stature, obesity and other abnormalities.
The pregnant mother carrying a triploidy fetus sometimes experiences increase in blood pressure (hypertension), swelling (edema), and excretion of albumin in the urine (albuminuria). This condition is called toxemia or preeclampsia. Triploidy is frequently diagnosed in pregnancies in which there is a cystic placenta (partial mole). Triploidy has been diagnosed in pregnancies that occur soon after oral contraceptives are discontinued or after long menstrual cycles. The disorder has been reported in conceptions that occurred following in vitro fertilization and in conceptions after a history of repeated miscarriages.
Triploidy is the presence of a complete additional set of chromosomes. The triplication of the chromosomes is caused by the fertilization of an egg by two sperms, or the fertilization of an egg by a sperm that has an extra set of chromosomes or by the fertilization of an egg that has an extra set of chromosomes by a normal sperm. This disorder does not run in families and is not associated with maternal or paternal age.
Triploidy accounts for 1-3 percent of all pregnancies. The condition occurs slightly more often in males than females; it is estimated that 2/3 of triploid pregnancies are male.
The presence of multiple major malformations, low amniotic fluid and/or growth restriction on fetal ultrasound during pregnancy raises the suspicion of triploidy. The diagnosis can be made during pregnancy by chromosome analysis (karyotyping) of cells obtained by amniocentesis or chorionic villus sampling (CVS). The diagnosis can be confirmed after birth by chromosome analysis of tissue (skin) obtained from the affected infant. Triploidy cannot be diagnosed by chromosome microarray testing. The accuracy of non-invasive prenatal testing using cell-free fetal (cff) DNA in the diagnosis of triploidy is still being studied. Abnormal levels of specific maternal blood proteins such as alpha-fetoprotein, human chorionic gonadotropin, estriol and pregnancy-assisted plasma protein-A have been associated with an increased risk for triploidy.
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