What is Copy Number Variation (CNV)? A 2026 Clinical Guide
At a Glance
- Sample Required: Peripheral blood (2-3 mL) or saliva sample
- Fasting Rules: No fasting required
- Turnaround Time (TAT): 10–14 business days
- Base Cost: [Insert Current 2026 Price]
Definition and Clinical Relevance
Copy number variation (CNV) refers to the duplication or deletion of DNA segments larger than 1 kilobase (kb) that alter the diploid status of the genome. These structural variants can be benign, pathogenic, or of uncertain significance. Pathogenic CNVs are implicated in numerous genetic disorders, including neurodevelopmental conditions, congenital anomalies, and cancer predisposition syndromes. Detection of CNVs is a cornerstone of modern genomic diagnostics.
Modern Detection Technologies
Advances in molecular genetics have replaced traditional cytogenetic methods with higher-resolution, genome-wide approaches. The following technologies are currently used in clinical practice:
Next-Generation Sequencing (NGS) – Whole Exome and Whole Genome
NGS, particularly whole exome sequencing (WES) and whole genome sequencing (WGS), now enables simultaneous detection of single-nucleotide variants (SNVs), indels, and CNVs. Bioinformatic algorithms analyze read-depth and allele frequency to identify copy number changes across the genome. This approach has largely replaced array-based methods for many indications due to its ability to detect both sequence and structural variants in a single assay.
Chromosomal Microarray (CMA) – Array Comparative Genomic Hybridization (aCGH)
CMA remains a robust and cost-effective method for CNV detection, especially in postnatal and prenatal settings. It uses oligonucleotide probes across the genome to detect copy number gains and losses with high resolution. While NGS is increasingly preferred, CMA is still widely used for its established interpretation guidelines and lower cost.
Targeted Assays – MLPA and FISH
Multiplex ligation-dependent probe amplification (MLPA) and fluorescence in situ hybridization (FISH) are now reserved for specific clinical scenarios, such as confirming a known familial CNV or detecting mosaicism. These methods are not genome-wide and are used to complement NGS or CMA findings.
Information Gain: Comparison of CNV Detection Methods
| Method | Resolution | Genome Coverage | Turnaround Time | Clinical Use |
|---|---|---|---|---|
| NGS (WES/WGS) | Exon-level to base-pair | Whole exome or genome | 10–14 days | First-line for many genetic disorders |
| Chromosomal Microarray (aCGH) | 50–100 kb | Genome-wide | 7–10 days | Postnatal and prenatal CNV screening |
| MLPA | Single exon to gene | Targeted regions | 3–5 days | Confirmation of specific CNVs |
| FISH | ~1 Mb | Targeted loci | 2–3 days | Rapid aneuploidy detection, mosaicism |
Clinical Significance and Interpretation
Interpreting CNVs requires careful classification based on size, gene content, population frequency, and inheritance patterns. Many CNVs are benign, but some are pathogenic with incomplete penetrance or variable expressivity. The American College of Medical Genetics and Genomics (ACMG) provides guidelines for CNV interpretation, which are routinely applied in our laboratory.
When a CNV of uncertain significance (VUS) is identified, additional familial testing or functional studies may be recommended. Genetic counseling is essential to explain the implications and guide clinical management.
When is CNV Testing Recommended?
- Neurodevelopmental disorders (e.g., autism, intellectual disability)
- Multiple congenital anomalies
- Cancer predisposition syndromes (e.g., hereditary breast and ovarian cancer, Lynch syndrome)
- Prenatal diagnosis of fetal structural abnormalities
- Unexplained developmental delay or regression
Why Choose DNA Labs India?
DNA Labs India is an ISO 9001 certified laboratory offering comprehensive genetic testing services. Our state-of-the-art NGS and CMA platforms provide accurate and reliable CNV detection. We adhere to strict quality control and provide expert interpretation by board-certified medical geneticists.