Clinical genomics is undergoing a profound transformation. The rapid evolution of sequencing technologies has given clinicians and researchers tools that were unimaginable just two decades ago — enabling the diagnosis of conditions that were previously undetectable, personalizing treatment at the molecular level, and opening new frontiers in reproductive health and oncology.
Three technologies sit at the heart of this revolution: Next-Generation Sequencing (NGS), cytogenetic testing, and Sanger sequencing. Each has distinct strengths, and together they form a comprehensive toolkit for understanding the human genome in clinical practice.
Next-Generation Sequencing (NGS)
Next-Generation Sequencing — also called high-throughput sequencing — is the most transformative technology in modern genomics. Unlike traditional Sanger sequencing, which reads one DNA fragment at a time, NGS processes millions of DNA fragments simultaneously — enabling rapid, cost-effective analysis of large amounts of genetic data.
Types of NGS in Clinical Practice
- Whole Exome Sequencing (WES) — Sequences only the protein-coding regions of the genome (the exome), which contain approximately 85% of disease-causing variants. Cost-effective for diagnosing rare genetic disorders and identifying variants of clinical significance.
- Whole Genome Sequencing (WGS) — Sequences the entire genome, including coding and non-coding regions. The most comprehensive approach; used for complex cases, research, and when WES is inconclusive.
- Targeted Panel Sequencing — Sequences a defined set of genes associated with a specific disease or condition. Efficient and cost-effective when the clinical question is focused (e.g., hereditary cancer panels, cardiac gene panels).
Clinical Applications of NGS
- Rare disease diagnosis — NGS has dramatically reduced the "diagnostic odyssey" for patients with rare genetic disorders, identifying causative variants in conditions that previously went undiagnosed for years
- Oncology — Identifying somatic mutations, copy number variations, and fusion genes in tumours to guide targeted therapy and immunotherapy decisions
- Pharmacogenomics — Identifying genetic variants that affect drug metabolism and response, enabling personalized prescribing
- Reproductive health — Carrier screening, preimplantation genetic testing (PGT), and non-invasive prenatal testing (NIPT)
- Infectious disease — Pathogen sequencing for outbreak investigation and antimicrobial resistance profiling
Cytogenetic Testing
Cytogenetic testing examines chromosomes — the large-scale structures that organize DNA in the cell nucleus. While NGS operates at the level of individual DNA base pairs, cytogenetic testing reveals structural abnormalities at the chromosomal level: translocations, deletions, duplications, inversions, and changes in chromosome number.
Key Cytogenetic Techniques
- Karyotyping — Microscopic examination of all 46 chromosomes; detects large structural abnormalities and aneuploidy (abnormal chromosome number)
- Fluorescence In Situ Hybridization (FISH) — Uses fluorescent probes to detect specific chromosomal regions; faster than karyotyping for targeted abnormalities
- Chromosomal Microarray (CMA) — Detects submicroscopic copy number variations (CNVs) — deletions and duplications too small to see by karyotyping but large enough to cause significant clinical effects
Clinical Applications of Cytogenetic Testing
- Prenatal diagnosis — Identifying chromosomal abnormalities in fetuses, including Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), and Turner syndrome
- Oncology — Diagnosing and prognosticating haematological malignancies (leukaemia, lymphoma) and solid tumours through characteristic chromosomal rearrangements
- Developmental delay and intellectual disability — Identifying chromosomal abnormalities underlying unexplained developmental delays
- Recurrent pregnancy loss — Detecting balanced translocations in parents that cause unbalanced chromosomal arrangements in embryos
Sanger Sequencing
Sanger sequencing — developed in the 1970s — was the gold standard of DNA sequencing for decades and remains an important tool in clinical genomics today. While NGS has largely replaced it for large-scale sequencing, Sanger sequencing retains a critical role as a validation method.
When Sanger Sequencing Is Used
- Variant confirmation — Validating specific variants identified by NGS before reporting them clinically; essential for quality assurance in diagnostic laboratories
- Targeted single-gene testing — Cost-effective when a specific known mutation is being tested (e.g., confirming a familial variant in relatives)
- Short sequence regions — Highly accurate for sequencing short, defined regions of interest
How These Technologies Work Together
In modern clinical genomics, these three technologies are complementary rather than competing:
- NGS identifies variants at the nucleotide level across large genomic regions
- Cytogenetic testing reveals chromosomal-level structural abnormalities that NGS may miss
- Sanger sequencing confirms specific variants identified by NGS with high accuracy
Together, they provide a comprehensive view of the genome — from individual base pairs to entire chromosomes — enabling more accurate diagnosis, better treatment decisions, and deeper understanding of genetic disease.
FAQs
What is the difference between WES and WGS?
Whole Exome Sequencing (WES) sequences only the protein-coding regions (about 1–2% of the genome), which contain most disease-causing variants. Whole Genome Sequencing (WGS) sequences the entire genome. WES is more cost-effective for most clinical applications; WGS is used when WES is inconclusive or when non-coding variants are suspected.
When is chromosomal microarray preferred over karyotyping?
Chromosomal microarray (CMA) is preferred when submicroscopic copy number variations are suspected — for example, in children with unexplained developmental delay, autism spectrum disorder, or multiple congenital anomalies. Karyotyping remains the standard for detecting balanced translocations and large chromosomal rearrangements.
🧬 MapmyGenome's Diagnostic Portfolio
MapmyGenome leverages NGS, cytogenetics, and Sanger sequencing across multiple clinical specialties — including reproductive health, oncology, rare diseases, and infectious diseases. Our CAP & NABL-accredited laboratory delivers accurate, clinically actionable results.
