Genetic testing for autism, ASD, and other developmental delay disorders are commonly performed using next-generation sequencing (NGS), chromosomal microarray analysis (CMA), or a combination of both techniques.
NGS is based on the process of DNA sequencing whereby the precise order of nucleotides within a DNA molecule is sequenced. With the development of recent technology, rapid DNA sequencing methods have evolved and have greatly accelerated biological and medical research. The rapid speed of sequencing attained with modern DNA sequencing technology has been instrumental in obtaining complete DNA sequences (genomes). The technique has wide application in many areas of biology, including medicine, forensics, and anthropology.
DNA sequencing can be used to determine the sequence of individual genes, larger genetic regions or clusters of genes (operons), full chromosomes, or entire genomes. In addition, DNA sequencing can also be used to efficiently sequence RNA.
Introduced in the past decade, NGS is also known as high-throughput sequencing. It is a powerful platform that has enabled the sequencing of thousands to millions of DNA molecules simultaneously. NGS has revolutionized the fields of personalized medicine, genetic diseases, and clinical diagnostics by offering a high throughput option with the capability to sequence multiple individuals at the same time.
Several companies have developed various types of NGS systems. Most, if not all, of these systems share at least three fundamental steps:
- DNA preparation and immobilization: This is also called library preparation, whereby libraries are created using random fragmentation of DNA. DNA is fragmented to create smaller strands. Short, double-stranded pieces of synthetic DNA are then ligated to these fragments with the help of DNA ligase, an enzyme that joins DNA strands. This enables the sequence to become bound to a complementary counterpart. Eventually, this process serves to build the DNA Library.
- Amplification: Amplification of the library using clonal amplification methods and polymerase chain reaction (PCR). Library amplification is required so that the received signal from the sequencer is strong enough to be detected accurately. There are several types of amplification process which use PCR to create large numbers of DNA clusters.
- Sequencing: DNA is sequenced using one of several different techniques.
