Postnatal Chromosome Analysis
Postnatal chromosome analysis is performed on peripheral blood, skin biopsy, or other specimens from individuals suspected of having a chromosome abnormality. Tissues from miscarried or stillborn babies can be tested for chromosome abnormalities, which are a significant cause of pregnancy loss.
What is a Chromosome Abnormality?
Chromosomes are units of genetic information. Every cell should have 46 chromosomes, arranged into 23 pairs. Differences in the number or the make-up of the chromosomes causes pregnancy loss, or mental retardation and birth defects in a live-born child. The most common chromosome abnormality is an extra 21 chromosome resulting in Down syndrome. Chromosome abnormalities are caused at conception when an abnormal sperm or egg from one parent fuses with a normal sperm or egg from the other parent. The abnormal sperm or egg contains extra or missing chromosomal material. These abnormal sperm or eggs are present in everyone, but the risk of an abnormal conception does increase significantly with the parents' ages.
Who Should Have Postnatal Chromosome Analysis?
- Newborns with three or more minor anomalies; that is, features which do not require surgery but are different from family members' features. The first signs of a chromosome abnormality in a newborn may be subtle differences in features.
- Newborns with differences of the genitalia; including a small penis, a displaced opening to the penis, and genitalia that is not completely female or male.
- Infants and children experiencing developmental delays, learning disabilities, behavioral problems, or unexplained mental retardation. Many children with chromosome abnormalities experience learning difficulties to some degree.
- Individuals suspected of having specific syndromes. A syndrome is a group of signs and symptoms which occur together and are typical of a particular disorder. The most common chromosomal syndrome is Down syndrome.
- Couples experiencing infertility or two or more pregnancy losses; including ectopic pregnancies, miscarriages, stillbirths, or unexplained neonatal deaths. In approximately 6% of these couples, one of the partners is a carrier of a chromosome abnormality.
- Females with inguinal hernia, absence of menstruation, and/or proportional short stature. Abnormalities of the X chromosome can cause these problems in females.
- Males with small testes or enlarged breasts (gynecomastia). Abnormalities of the X chromosome can cause these problems in males.
- Females with premature ovarian failure, or early menopause.
- Males with oligospermia or azoospermia (low or absent sperm count) because 4.6-13.7% have a chromosome abnormality. All males seeking assisted reproductive technology should have chromosome analysis and Y-DNA deletion studies.
- Tissues of miscarried or stillborn babies in cases of unexplained pregnancy loss. About 60% of these losses are due to a chromosome abnormality.
- Blood relatives of individuals with a chromosome abnormality. These relatives are at risk for carrying a balanced form of the chromosome abnormality which could be passed to their children in an unbalanced state, causing miscarriage and/or birth defects and mental retardation.
What Other Testing Should be Performed on Postnatal Specimens?
Some abnormalities of the chromosomes cannot be detected with standard chromosome analysis. Many chromosome deletions are so small (micro) they cannot be detected by chromosome analysis alone. A specific laboratory technique know as FISH (fluorescent in situ hybridization) is used to look for micro-deletions known to cause certain genetic syndromes. A variety of specialized testing is available to detect other types of chromosome abnormalities.
Please contact GeneCare at 800-277-4363 and speak to a genetic counselor if you have further questions about postnatal chromosome analysis.
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Last modified: May 25, 2004 04:26 PM
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