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Neonatal blood Aneuploidy screening - FISH 3 probes(18, X & Y)
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Chromosomal abnormality detection.
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Neonatal Blood Aneuploidy Screening-FISH 3 Probes (18, X & Y)
- Why is it done?
- Detects chromosomal abnormalities using Fluorescence In Situ Hybridization (FISH) technology to identify trisomy 18 (Edwards syndrome), trisomy 21 (Down syndrome), and sex chromosome abnormalities (X and Y)
- Primary indication: Screening newborns with abnormal prenatal screening results or clinical features suggestive of chromosomal disorders
- Performed in neonates (typically within first 24-48 hours of life) with suspected chromosomal abnormalities based on maternal serum screening, ultrasound findings, or clinical presentation
- Provides rapid cytogenetic diagnosis as a preliminary screening tool prior to comprehensive chromosomal analysis
- Used for identification of sex chromosome disorders (Turner syndrome, Klinefelter syndrome, XXX syndrome, XYY syndrome)
- Normal Range
- Normal Result (Negative): Two copies of chromosome 18, normal sex chromosomes (XX for females, XY for males), with no numerical abnormalities detected
- Expected Values: 2 signals for chromosome 18 probe, 1 X or 1 Y signal (or 1X + 1Y for males), indicating normal diploid number
- Abnormal Result (Positive): Three copies of chromosome 18 (trisomy 18), three copies of chromosome 21 (trisomy 21), or abnormal sex chromosome patterns
- Units of Measurement: Number of fluorescent signals (probes) per cell nucleus (quantitative count)
- Interpretation Guide: Normal = 2:2:2 or 2:2:1 pattern (chromosome 18: X/Y: normal); Abnormal = 3:2:2 (trisomy 18), 3:2:1 (XYY), 1:1:0 (monosomy X), 2:2:0 (nullisomy), or other variants indicating aneuploidies
- Interpretation
- Trisomy 18 (Edwards Syndrome): Three copies of chromosome 18 detected; associated with severe developmental abnormalities, cardiac defects, renal anomalies, and poor prognosis
- Trisomy 21 (Down Syndrome): Note: This panel detects chromosome 18 primarily; chromosome 21 is detected via the additional probe. Three copies indicate Down syndrome with intellectual disability and characteristic features
- Sex Chromosome Abnormalities - 45,X (Turner Syndrome): Absence of X or Y signal; monosomy X indicated by single signal for sex chromosomes; associated with short stature, infertility, cardiac defects
- Sex Chromosome Abnormalities - 47,XXY (Klinefelter Syndrome): Two X signals and one Y signal detected; associated with infertility, hypogonadism, tall stature with long legs
- Sex Chromosome Abnormalities - 47,XYY (XYY Syndrome): Two Y signals and one X signal; generally benign, associated with tall stature and possible learning difficulties
- Sex Chromosome Abnormalities - 47,XXX (Triple X Syndrome): Three X signals detected; often clinically silent with variable expression; may have mild intellectual disability or infertility
- Factors Affecting Results: Mosaicism (abnormal cells in <50% of cells may not be detected); maternal cell contamination; poor sample quality or insufficient cells; concurrent medical conditions; specimen processing delays
- Clinical Significance: FISH testing provides rapid preliminary results (24-48 hours) compared to conventional karyotyping (7-14 days); limited to specific chromosomes and cannot detect balanced rearrangements or small deletions/duplications
- Associated Organs
- Primary Organ Systems: Central nervous system (CNS), cardiovascular system, genitourinary system, musculoskeletal system (all systems affected by chromosomal abnormalities)
- Trisomy 18 Associated Conditions: Congenital heart defects (ventricular septal defect, atrial septal defect, patent foramen ovale), renal abnormalities, cleft palate, cognitive disability, growth restriction, multiple organ involvement
- Trisomy 21 Associated Conditions: Intellectual disability, distinctive facial features (upslanting palpebral fissures, flat nasal bridge), cardiac anomalies, gastrointestinal disorders, increased risk of leukemia and Alzheimer disease
- Turner Syndrome (45,X) Associated Conditions: Short stature, gonadal dysgenesis, infertility, cardiac defects (bicuspid aortic valve, coarctation of aorta), hearing loss, kidney abnormalities
- Klinefelter Syndrome (47,XXY) Associated Conditions: Hypogonadism, infertility, low testosterone levels, gynecomastia, tall stature with long legs, possible learning or behavioral difficulties
- Potential Complications: Cardiac failure, respiratory complications, feeding difficulties, developmental delay requiring early intervention, metabolic complications, increased infection risk
- Follow-up Tests
- Conventional Karyotyping: Confirmatory test providing complete chromosomal analysis; detects balanced rearrangements, mosaicism, and other structural abnormalities; typically ordered following positive FISH results
- Microarray Analysis (Array CGH or SNP Array): Detects submicroscopic deletions and duplications not visible on conventional karyotyping; provides high-resolution copy number analysis
- Echocardiography: Recommended within first week of life if aneuploidy detected; evaluates cardiac structure and function, screens for congenital heart defects common in chromosomal disorders
- Ultrasound Imaging (Abdominal/Renal): Assesses for genitourinary and renal anomalies; evaluates gastrointestinal structure; screens for associated organ involvement
- Audiometric Testing: Hearing screening particularly important in Turner syndrome and trisomy 18; performed before discharge or by 1 month of age per newborn screening protocols
- Genetic Counseling: Recommended for families with positive aneuploidy results; discusses prognosis, management options, inheritance patterns, and recurrence risk for future pregnancies
- Metabolic Screening: Expanded newborn screening panel as per state/regional protocols; includes thyroid function tests, particularly relevant for Down syndrome (high hypothyroidism risk)
- Developmental Screening: Early intervention programs, developmental assessment at regular intervals (3, 6, 12 months); ongoing monitoring for developmental delays
- Parental Chromosomal Testing: Recommended when mosaicism or rare aneuploidy patterns identified; rules out balanced translocation carrier status in parents
- Fasting Required?
- Fasting Required: No
- Special Preparation Instructions: No special fasting or dietary restrictions required; test can be performed at any time of day
- Specimen Collection: Peripheral blood sample (typically 2-5 mL) collected in sterile tube with appropriate anticoagulant (lithium heparin or EDTA); collected via venipuncture or heel prick in neonates
- Timing of Collection: Preferably within first 24-48 hours of life for optimal cell viability and rapid turnaround time; can be collected up to 7 days after birth if needed
- Medications to Avoid: No medications need to be withheld; test is not affected by neonatal medications (antibiotics, vitamin K, etc.)
- Transport and Storage: Specimen should be transported at room temperature for FISH analysis; do not refrigerate or freeze blood samples for FISH; deliver to laboratory within 24-48 hours for best results
- Additional Patient Preparation: Ensure informed consent obtained from parents/guardians prior to testing; explain test purpose, limitations, and potential outcomes; provide genetic counseling information if available
How our test process works!
