Clinical Conditions
Down syndrome
Down syndrome, also know as trisomy 21, is a genetic disorder that occurs when the 21st pair of chromosomes has an extra copy or third chromosome, instead of the usual two chromosomes. Having an extra chromosome is called a “trisomy.”
Most individuals have a total of 46 chromosomes arranged in 23 pairs. These 23 pairs are numbered 1-22 and the 23rd pair, designated as XY determines the sex of the baby. Chromosomes control growth and development and are considered as transmitters of genetic material. Chromosomal imbalances, such as in trisomy, often result in abnormal development of the fetus.
The degree of physical and mental retardation for individuals affected by trisomy 21, or Down syndrome, varies greatly. For some it is minimal; for others it is substantial. Chromosomal imbalances often lead to a combination of malformations, which may include flattened facial features and retardation of both physical and mental growth. All Down syndrome cases have some degree of mental impairment. Congenital heart disease, a major cause of early death associated with Down syndrome, can often be corrected by surgery. Recent advances in education have enabled certain Down syndrome children to live more independent and productive lifestyles. Down syndrome occurs in about one in 800 births; however the incidence rate varies significantly by maternal age.
Trisomy 18
Trisomy 18 is a type of chromosomal abnormality in which the 18th pair of chromosomes has an extra or third chromosome instead of the usual two chromosomes. Trisomy 18 is considered a more severe disorder than Down syndrome. Approximately 30% of babies born with trisomy 18 die within the first month of birth, 50% by two months, 70% by three months, 90% by one year of age and 99% by age 10. The survivors are profoundly retarded in both physical and mental growth. Trisomy 18 occurs in one out of every 6,600 births.
Trisomy 13
Trisomy 13 is a chromosomal disorder that occurs in approximately 1 in 10,000 live born infants. The condition is attributed to the presence of an extra chromosome 13. Infants born with trisomy 13 have a recognizable pattern of physical features such as a small head size (microcephaly), small eyes (micropthalmia), or sometimes absent eye or faulty retinal development. Cleft lip or cleft palate or both occur in approximately 60% of children born with this disorder. About 80% of trisomy 13 cases will have congenital heart defects. Other potential considerations include feeding difficulties, gastroescophageal reflux, slow post-natal growth, apnea, seizures, hypertension, kidney defects, developmental disabilities and scoliosis.
Open Neural Tube Defects (ONTD)
Open neural tube defects affect the head and spine of the baby, including spina bifida and anencephaly. They occur when the neural tube (the structure that later develops into the brain and spinal cord) remains open instead of closing during embryonic growth in the first month of pregnancy.
Common Types of Neural Tube Defects
Anencephaly (an-en-sef-a-lee) is a disorder in which much of the brain and head are underdeveloped. Newborns usually do not survive after birth. Anencephaly occurs in one out of 1,500 pregnancies, but incidence rates vary by geography and ethnicity.
Open spina bifida involves an opening in the spinal column of the baby. Open spina bifida is often accompanied by conditions with varying degrees of severity including paralysis of the legs, lack of bowel or bladder control and an accumulation of excess fluid in the brain. In a small percentage of open spina bifida newborns, the birth defect is minor. Open spina bifida occurs in about 1 out of 2,000 pregnancies but incidence rates may vary based upon a number of factors, including geography and ethnicity.
Closed spina bifida is a defect of the spinal column which is covered by skin or membranous tissue. The closed form of spina bifida may lead to serious medical conditions and is rarely detectable by prenatal screening.
Ventral Wall Defects (VWDs) are characterized by an opening in the abdomen through which a part of the intestine may protrude. These birth defects are rare, occurring in about 1 out of every 5,000 births.
To determine whether or not your pregnancy is at increased risk for ONTDs and VWDs, NTD Labs measures a naturally occurring substance in the blood known as alpha-fetoprotein (AFP), which is produced by the liver of the baby. When ONTDs or VWDs are present, the expectant mother’s blood usually contains elevated levels of AFP. However, elevated levels of AFP may also occur in normal pregnancies as well.