Retinoblastoma Chromosome Abnormalities
Norm of Retinoblastoma Chromosome Abnormalities
Female |
44 autosomes + 2X chromosomes |
| Karyotype | 46,XX |
Male |
44 autosomes + 1X and 1Y chromosome |
| Karyotype | 46,XY |
Note: Retinoblastoma chromosomal defect is identified as female, 46,XX,13q-; male, 46,XY,13q-.
Usage of Retinoblastoma Chromosome Abnormalities
Screening for retinoblastoma, identification of numerical chromosomal defects, and genetic counseling.
Description of Retinoblastoma Chromosome Abnormalities
Retinoblastoma is an inherited type of cancer caused by mutations of the RB1 gene. It is the most frequently occurring congenital ocular tumor in children, occurring in 1 in 20,000 births. Tumor occurrence is unilateral in 60% of cases and is usually nonmetastatic and may occur up to several years later in the second eye. The risk for metastasis of retinoblastoma is elevated when diagnosis is delayed, when both eyes are involved, and when there is invasion to the uvea, orbit, and optic nerve. Clinical symptoms include strabismus, impaired vision, and the appearance of white to yellow reflex from the pupil, referred to as “cat's-eye.” Left untreated, this tumor is fatal because optic nerve, subarachnoid space, and cerebral tissue invasion occurs. If caught early enough, retinoblastoma is considered curable with years of chemotherapy treatment. Leukocyte screening of peripheral blood is the most common technique for chromosomal abnormality detection and analysis. Tissue cultures are cultivated from the blood sample, fixed, and stained. The chromosomes are then counted and photographed, and the karyotype is arranged according to the Denver nomenclature from cut photographs. Diagnosis is confirmed by computed tomography with or without magnetic resonance imaging, and radiotherapy is a common approach to treatment. Prognosis is dependent on location, size, and the amount of ocular and extraocular involvement.
Professional Considerations of Retinoblastoma Chromosome Abnormalities
Consent form NOT required.
Preparation
- See Client and Family Teaching.
- Tube: Green topped.
- Specimens MAY be drawn during hemodialysis.
Procedure
- A morning sample is preferred. Draw a 10-mL blood sample.
Postprocedure Care
- None.
Client and Family Teaching
- This test is a genetic screen.
- Fast for 3 hours before the blood is drawn.
Factors That Affect Results
- Insufficient number of cells in sample.
Other Data
- Retinoblastoma is also associated with elevated plasma somatostatin levels.
