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Alpha-fetoprotein --- The predominant protein present in fetal blood. Small amounts are present in the maternal circulation during pregnancy, and the values change as the fetus grows. Abnormally high or low values are associated with increased risks of spina bifida and Down syndrome, respectively.
Amniocentesis --- A procedure for prenatal diagnosis in which about one tablespoon of amniotic fluid surrounding the fetus is withdrawn from the amniotic sac using a very fine needle. Genetic amniocentesis is performed at The Genetics Center. Continuous ultrasound guidance during the amniocentesis makes the 60 to 90 second procedure as safe and painless as possible.
Autosomal recessive / dominant --- Patterns of inheritance in which females are as likely to be affected as males. In recessive disorders, one gene (of the pair) needs to function properly to prevent the disorder. For a dominant disorder, one gene functioning abnormally is sufficient to cause the disorder.
BRCA1 and BRCA2 --- Two genes that are important in breast cancer. Certain changes in either BRCA1 or BRCA2 result in an increased risk of developing breast, ovarian, or certain other cancers. BRCA1 was identified in 1994, and BRCA2 was discovered in 1996.
Carrier --- An individual who has one non-functioning gene for a recessive disorder can transmit that gene to his or her offspring. Carriers most often have no outward manifestations of their condition.
Chromosomes --- Microscopic structures, present in the nucleus of each cell, which contain all of our genes. Abnormal size or number of chromosomes is a cause of some birth defects and mental retardation.
Chorionic villus sampling (CVS) --- A prenatal diagnostic technique to obtain fetal cells from the placenta. This can be performed several weeks earlier than amniocentesis, albeit with a somewhat higher risk of procedure related complications.
Cytogenetics --- The study of chromosomes. The Genetics Center has a fully licensed cytogenetics laboratory directed by Dr. Carolyn Trunca.
DNA --- The molecule which contains each individual cell's genetic code. In humans, DNA is organized into 23 pairs of chromosomes.
Down syndrome --- A condition involving mental retardation and distinctive facial features which is due to an extra chromosome 21. This can be detected prenatally by chromosome analysis on fetal cells obtained by amniocentesis.
Familial --- Occurring in more than one family member. A familial condition may be due to an inherited (genetic) factor, more than one genetic factor, an environmental factor, or some combination of these.
Gene --- A portion of a chromosome, too small to be seen under a microscope, which encodes a particular function. Humans are estimated to have approximately 50,000 different genes. Abnormalities of genes can cause various problems, depending on the gene involved and specific changes within that gene.
Genetic consultation --- An opportunity to meet with a geneticist to deal with genetic issues. A physician requests a consultation for a specific reason. After evaluating the situation, conducting any necessary tests, and counseling the patient, the geneticist summarizes the recommendations in a written report to the referring physician.
Genetic counseling --- Performed by a geneticist or a genetic counselor supervised by a geneticist, counseling is the process of conveying genetic information specific to the family and medical situation.
Geneticist --- A physician or PhD with special training in human genetics. Medical Genetics is a specialty recognized by the American Board of Medical Specialties. The geneticists at The Genetics Center are board-certified.
Human chorionic gonadotropin (hCG) --- A hormone produced by the placenta during a pregnancy. Measurement of this hormone is the basis of pregnancy tests. An unusually high level of this hormone in the second trimester is one reason that further testing for Down syndrome may be recommended. An unusually low level may indicate a rare chromosome abnormality called trisomy 18.
Maternal serum screening --- A blood test taken at 14-20 weeks gestation to determine whether there is an increased risk for a fetus having Down syndrome, trisomy 18, or spina bifida. The test is also known as the alpha-fetoprotein or AFP test, triple screen, or quad screen, depending on which combination of substances are measures on the blood sample.
Multifactorial inheritance --- A pattern of inheritance exhibited by a number of conditions, such as heart disease, diabetes, and certain birth defects. Multiple genetic or non-genetic factors--not just one--are involved in causing a Multifactorial condition.
Mutation --- A permanent, heritable change in the DNA of a particular gene.
Presymptomatic testing --- Testing to determine whether a particular condition will develop in the future. Presymptomatic testing for breast cancer involves analyzing the BRCA1 and BRCA2 genes.
Risk assessment --- Determining the chance of a particular outcome by using a combination of family history and laboratory testing. An example of this is predicting breast cancer risk for a woman with a family history of breast cancer who has had BRCA gene testing.
Spina bifida --- A birth defect caused when the neural tube, the structure in the very early embryo which develops into the brain and spina cord, fails to close properly. Spina bifida due to a neural tube defect typically results in paralysis as well as hydrocephalus ("water on the brain"). Anencephaly is a severe form of a neural tube defect in which no normal brain tissue develops. Spina bifida occulta is a minor defect of the spine which is not related to spina bifida from an open neural tube defect.
Translocation --- A chromosome rearrangement in which the chromosomes are not arranged in the typical set of 23 pairs. Even if the correct amount of genetic material is present, an individual with a chromosome translocation is at increased risk for having problems such as difficulty conceiving or maintaining a pregnancy. Chromosome translocations are often inherited.
Trisomy --- Having three of a given chromosome instead of the usual two. Trisomy for chromosome 21 is the cause of Down syndrome. Trisomy for chromosome 18 and trisomy for chromosome 13 cause very serious birth defects.
Ultrasonography --- The use of high frequency sound waves to examine internal body structures, such as a fetus contained in the uterus. An ultrasound examination is also known as a sonogram.
X-linked --- Hemophilia, Duchenne muscular dystrophy, and color blindness are examples of diseases whose genes are located on the X chromosome. Males are most often affected with X-linked disorders. This is the same as the formerly used term, sex-linked.