Circumstances in which the parents are not emotionally capable of understanding the test results and managing the ramifications of the test results.
Synonym/Acronym
chromosome karyotyping.
Rationale
To test for suspected chromosomal disorders that result in birth defects such as Down syndrome.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
(Method: Tissue culture and microscopic analysis). No chromosomal abnormalities identified.
(Study type: Blood collected in a green-top [sodium heparin] tube; related body system: .)
Cytogenetics is a specialization within the area of genetics that includes chromosome analysis or karyotyping. Chromosome analysis or karyotyping involves comparison of test samples against normal chromosome patterns of number and structure. A normal karyotype consists of 22 pairs of autosomal chromosomes and one pair of sex chromosomes, XX for female and XY for male. Variations in number or structure can be inherited or acquired. Variations can range from a small, single-gene sequence variation to abnormalities in an entire chromosome or set of chromosomes due to duplication, deletion, substitution, translocation, or other rearrangement.
Molecular probe techniques are used to detect smaller, more subtle changes in chromosomes. Cells are incubated in culture media to increase the number of cells available for study and to allow for hybridization of the cellular DNA with fluorescent DNA probes in a technique called fluorescence in situ hybridization (FISH). The probes are designed to target areas of the chromosome known to correlate with genetic risk for a particular disease. When a suitable volume of hybridized sample is achieved, cell growth is chemically inhibited during the prophase and metaphase stages of mitosis (cell division), and cellular DNA is examined to detect fluorescence, which represents chromosomal abnormalities, in the targeted areas. Amniotic fluid, chorionic villus sampling, and cells from fetal tissue or products of conception can also be evaluated for chromosomal abnormalities.
Cell free fetal DNA (cffDNA) analysis is a noninvasive cytogenetic screening option for females of reproductive potential with an increased risk for fetal aneuploidy (an abnormal number of fetal chromosomes). CffDNA is released by the placenta as early as the 10th week of pregnancy and is detectable in circulating blood of the biological mother. Analysis of the blood sample can be performed to identify trisomy 13 (Patau syndrome), trisomy 18 (Edwards syndrome), trisomy 21 (Down syndrome), and Klinefelter syndrome (XXY). It should be noted that there are a number of limitations with cffDNA testing that would not be encountered with conventional prenatal screening and diagnostic testing strategies. Discussion regarding the limitations and benefits should occur between every patient who chooses this testing and the appropriate health-care provider (HCP). The most current screening recommendations for aneuploidy include a requirement that all cffDNA screens be confirmed by a diagnostic test such as amniocentesis or chorionic villus sampling, regardless of whether the screening test results were normal or abnormal. For additional information regarding maternal screening, refer to the study titled “Prenatal Screening Tests.”
Cytogenetic testing is also used to identify conditions associated with the reproductive system. For example, gene sequence variations that affect normal functioning of the ovaries have been associated with amenorrhea and the subsequent development of infertility issues. The chromosomal abnormalities may be inherited or acquired.
Knowledge of genetics assists in identifying those who may benefit from additional education, risk assessment, and counseling. Genetics is the study and identification of genes, genetic sequence variations, and inheritance. For example, genetics provides some insight into the likelihood of inheriting a medical condition such as Down syndrome. Down syndrome is an example of a chromosome disorder in which the cells have three copies of chromosome 21 (trisomy) instead of the normal two copies. Further information regarding inheritance of genes can be found in the study titled “Genetic Testing.”
Circumstances in which the parents are not emotionally capable of understanding the test results and managing the ramifications of the test results.
The following tables list some common genetic defects.
| Syndrome | Autosomal Chromosome Defect | Features |
|---|---|---|
| Angelman | Deletion 15q11–q13 | Developmental delays (physical growth, communication, and motor skills); hyperactive behavior; overall happy demeanor with frequent laughter and hand-flapping actions; fascination with water |
| Beckwith-Wiedemann | Duplication 11p15 | Macroglossia, omphalocele, earlobe creases |
| Bloom | Sequence variations of BLM, 15 | Birth weight and length are below normal, and stature remains below normal to adulthood; skin changes in response to sun exposure; increased risk of cancers that develop early in life; high-pitched voice; distinctive facial features (long, narrow face with a small jaw; large nose and ears) |
| Canavan | Sequence variations of ASPA, 17p13.3 | Developmental delays that become obvious at 3 to 5 months of age; hypotonia that contributes to inability to roll over, sit upright, or swallow; macrocephaly; and intellectual disability |
| Cat’s eye | Trisomy 2q11 | Anal atresia, coloboma |
| Cri du chat | Deletion 5p | Catlike cry, microcephaly, hypertelorism, intellectual disability, retrognathia |
| Cystic fibrosis | Sequence variations of CFTR, 7 | Impaired transport of chloride affects the movement of water in and out of the cells lining the lungs and pancreas, resulting in production of thick mucus that obstructs airways and prevents normal function of the affected organs; life-threatening, permanent lung damage |
| DiGeorge | Deletion 22q11.2 | The wide variety in type and severity of problems associated with this syndrome of impaired development of body systems most commonly includes cardiac abnormalities or defects, poor immune system function (hypothymic or absent thymus), cleft palate, hypoparathyroidism (low calcium), behavioral disorders, distinctive facial features (long face with downturned mouth, asymmetric face when crying, microcephaly, hooded eyelids, malformed ears) |
| Down | Trisomy 21 | Epicanthal folds, simian crease of palm, flat nasal bridge, intellectual disability, congenital heart disease |
| Edwards | Trisomy 18 | Micrognathia, clenched third/fourth fingers with the fifth finger overlapping, rocker-bottom feet, intellectual disability, congenital heart disease |
| Gaucher | Genetic sequence variations of GBA, 1 | Hepatomegaly and splenomegaly related to accumulation of lipids, anemia, thrombocytopenia, bone disease (bone pain, fractures, and arthritis) |
| Maple syrup | Genetic sequence variations of BCKDHA, BCKDHB, DBT, and DLD, 19 | Developmental delays, poor feeding, lethargy, distinctive maple syrup odor in urine |
| Miller-Dieker | Deletion 17 | Lissencephaly (incomplete or absent development of the folds of the cerebrum); microcephaly; developmental delays, especially in growth; intellectual disability with seizures; difficulty feeding and failure to thrive; cardiac malformations |
| Niemann-Pick | Chromosome 14q24.3 (type C2); 18q11.2 (type C1); 11p15.4–p15.1 (types A & B) | All types demonstrate symptoms that reflect abnormalities in liver and lung function; blood tests show hyperlipidemia (cholesterol and other fats) and thrombocytopenia |
| Pallister-Killian | Trisomy 12p | Psychomotor delay, sparse anterior scalp hair, micrognathia, hypotonia |
| Patau | Trisomy 13 | Microcephaly, cleft palate or lip, polydactyly, intellectual disability, congenital heart disease |
| Prader-Willi | Deletion 15q11–q13 | Delayed development; distinctive facial features (narrow forehead, almond-shaped eyes, triangular-shaped mouth, diminished stature with small hands and feet); hypotonia; childhood development of an insatiable appetite, hyperphagia, and obesity; mild to moderate intellectual disability; behavioral problems (outbursts of anger and compulsive behavior such as picking at the skin) |
| Smith-Magenis | Deletion 17p11.2 | Major features include mild to moderate intellectual disability, delayed speech and language skills, distinctive facial features, sleep disturbances, and behavioral problems |
| Tay-Sachs | Genetic sequence variations of HEXA, 15q24.1 | Normal development until age 3 to 6 mo when development slows and hypotonia affects motor skills such as ability to turn over, sit upright, and crawl; exaggerated startle reaction to loud noises; seizures; eventual loss of vision (cherry red spot upon eye examination is characteristic) and hearing; intellectual disability |
| Warkam | Mosaic trisomy 8 | Malformed ears, bulbous nose, deep palm creases, absent or hypoplastic patellae |
| Wolf-Hirschhorn | Deletion 4p16.3 | Microcephaly, growth retardation, intellectual disability, carp mouth |
| Syndrome | Sex-Chromosome Defect | Features |
|---|---|---|
| Fragile X | Xq27.3 | Intellectual disability, autism and autism spectrum disorders |
| XYY | 47,XYY | Tall, increased risk of behavior problems |
| Klinefelter | 47,XXY | Hypogonadism, infertility, underdeveloped secondary sex characteristics, learning disabilities |
| Rett | Genetic sequence variations of Xq28 | Severe and progressive developmental problems related to brain functions such as speech, motor, and intelligence begin after 6 to 18 mo of normal growth; brain disorder almost exclusively affecting females; slower than normal physical growth; microcephaly; meaningful use of hands is lost in early childhood and replaced by repetitive random hand motions such as clapping or wringing |
| Triple X | 47,XXX | Increased risk of infertility and learning disabilities |
| Ullrich-Turner | 45,X | Short, gonadal dysgenesis, webbed neck, low posterior hairline, renal and cardiovascular abnormalities |
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
Clinical Judgement
Follow-Up Evaluation and Desired Outcomes