Next-generation sequencing (NGS) is a powerful and versatile genomic technology used for high-throughput DNA and RNA sequencing. Its applications in pediatrics are expanding due to its ability to provide precise genetic diagnoses.
What is Next-generation sequencing NGS?
NGS refers to advanced sequencing technologies that allow parallel sequencing of millions of DNA fragments. This technology provides a comprehensive view of the genome, exome (coding regions of genes), or transcriptome (RNA).
Techniques of NGS
- Whole Genome Sequencing (WGS): Sequences the entire genome, including coding and non-coding regions.
- Whole Exome Sequencing (WES): Focuses on coding regions (exons) of the genome, which comprise approximately 1% of the genome but harbor the majority of known disease-causing mutations.
- Targeted Gene Panels: Focus on specific sets of genes associated with a particular disease or group of disorders.
- RNA Sequencing (RNA-seq): Provides information about gene expression and structural variations in RNA.
Indications for NGS in Pediatrics
NGS is particularly useful in identifying genetic causes of diseases in children, especially in the following scenarios:
1. Unexplained Developmental Disorders and Intellectual Disabilities
- Suspected genetic etiology without a definitive diagnosis despite extensive evaluation.
- Congenital malformations or syndromic presentations without a clear cause.
2. Rare Mendelian Disorders
- Monogenic disorders such as inherited metabolic diseases, primary immunodeficiencies, or connective tissue disorders.
- Conditions where conventional genetic tests like karyotyping and microarrays have failed to identify a cause.
3. Neurological Disorders
- Early-onset epilepsy with suspected genetic cause.
- Neurodegenerative disorders and leukodystrophies.
- Movement disorders, including dystonia and ataxia.
4. Hematological and Oncological Disorders
- Identification of germline mutations in hereditary cancer syndromes (e.g., Li-Fraumeni syndrome).
- Diagnosis and classification of leukemias and solid tumors.
- Predicting response to targeted therapies based on tumor-specific genetic alterations.
5. Inherited Cardiomyopathies and Arrhythmias
- Hypertrophic or dilated cardiomyopathies.
- Long QT syndrome or other inherited arrhythmogenic disorders.
6. Primary Immunodeficiencies
- Suspected genetic immunodeficiencies such as severe combined immunodeficiency (SCID) or chronic granulomatous disease.
7. Autism Spectrum Disorders
- When associated with dysmorphism, malformations, or a positive family history suggesting a genetic basis.
8. Reproductive and Preimplantation Testing
- Carrier screening in parents for inherited conditions.
- Preimplantation genetic testing in assisted reproductive techniques.
9. Genomic Syndromes
- Complex syndromes with overlapping phenotypes where single-gene tests are inconclusive.
Benefits of NGS in Pediatrics
- Higher Diagnostic Yield: Especially in rare disorders with a genetic basis.
- Cost-Effectiveness: Particularly when compared to performing multiple sequential genetic tests.
- Precision Medicine: Guides personalized treatment based on molecular diagnosis.
Challenges and Limitations
- Variants of Uncertain Significance (VUS): Difficulty in interpreting the clinical relevance of certain genetic variants.
- Incidental Findings: Discovery of unrelated but potentially actionable genetic information.
- Ethical and Counseling Issues: Requires robust pre- and post-test genetic counseling.
- Cost and Accessibility: Still a barrier in many low-resource settings.