New rapid blood test may diagnose most SMA cases in about one hour
Experimental assay skips DNA purification to deliver results more quickly
Written by |
- SMA is a genetic neuromuscular condition primarily caused by mutations in the SMN1 gene.
- An experimental rapid blood test can diagnose most SMA cases in about one hour.
- The LNA-PCR assay detects common SMN1 deletions without requiring DNA purification.
A new blood test may offer a faster and simpler way to reliably diagnose most cases of spinal muscular atrophy (SMA), with results available in about one hour, a study showed.
The LNA-PCR assay looks for homozygous SMN1 deletions, the most common SMA-causing mutation, in which a key section of both copies of the SMN1 gene is missing. Unlike standard genetic testing approaches that require DNA to be extracted and purified from a blood sample, the new test works directly from blood after a simple preparation step.
The experimental assay correctly identified 95% of people with a confirmed homozygous SMN1 deletion and produced no false-positive results among validated controls without such a deletion.
“The direct LNA-PCR assay enables rapid, reliable, and cost-effective detection of homozygous SMN1 deletions directly from blood samples without DNA purification,” researchers wrote. “This simplified workflow may facilitate broader implementation of molecular testing for SMA in routine clinical laboratories and resource-limited settings.”
The study, “A rapid LNA-PCR assay from blood lysate without DNA purification for the diagnosis of homozygous SMN1 deletion in spinal muscular atrophy,” was published in Scientific Reports.
Molecular diagnostic methods can be costly, time-consuming
A genetic disease, SMA is mostly caused by mutations in the SMN1 gene, which lead to inadequate production of the survival motor neuron (SMN) protein. This causes the progressive loss of motor neurons, the nerve cells that control movement, resulting in muscle weakness and wasting.
The most common disease-causing mutation, accounting for about 95% of cases, is the complete loss of exon 7 in both copies of the SMN1 gene. Exons are the sections of a gene that contain instructions for protein production. This mutation essentially causes a chunk of the genetic code to be missing, which interferes with SMN production.
“Early and reliable molecular diagnosis is essential for clinical management, genetic counseling, and implementation of emerging therapeutic interventions,” the researchers wrote. “However, many molecular diagnostic methods require DNA purification and complex laboratory workflows, which may increase turnaround time and cost.”
Researchers simplified earlier test
Researchers in Turkey had previously developed a PCR-based test, called LNA-PCR, to detect SMN1 using purified DNA. PCR, short for polymerase chain reaction, works by repeatedly copying a specific stretch of DNA until there is enough of it to be detected. In this case, the test targets exon 7 of SMN1. If it is present, PCR produces a signal; if it is missing from both copies of the gene, no SMN1 signal is detected.
In this study, the team sought to simplify the process by eliminating the DNA purification step. Instead, blood was diluted and heated to break open cells and release their genetic material, then centrifuged before the resulting liquid was used for PCR.
The researchers evaluated the LNA-PCR assay using blood samples from 792 people. These included 61 people with genetically confirmed SMA, 56 SMA carriers, meaning they had one functional copy of SMN1, 45 genetically tested healthy controls, and another 630 healthy people older than 40 with no SMA-related symptoms.
Of the 61 people with SMA, 60 had the homozygous SMN1 deletion the new test was designed to detect. The LNA-PCR assay correctly identified 57 of these 60 cases, corresponding to a sensitivity of 95% — meaning it detected 95% of those known to have homozygous SMN1 deletion.
This approach enables rapid and reliable identification of SMA patients with homozygous SMN1 deletion directly from whole blood samples and may serve as a practical first-line diagnostic tool for SMA.
The other person with SMA had a different genetic cause of the disease: a deletion in one copy of SMN1 and a disease-causing point mutation, or a change in a single DNA building block, in the other. Because one SMN1 copy was still present, the assay produced a signal and correctly indicated that this person did not have a homozygous deletion.
The assay also correctly detected an SMN1 signal in all 56 carriers and 45 healthy controls. Together with the person with SMA who did not have a homozygous deletion, this meant it correctly classified all 102 genetically validated samples without the deletion, for a specificity of 100%. In other words, it did not falsely identify a homozygous deletion in any of these samples.
All 630 additional adults with no clinical signs of SMA also showed an SMN1 signal. However, because their SMN1 status had not been independently confirmed by genetic testing, they were not included in calculations of the assay’s diagnostic performance.
Overall, the assay had a diagnostic accuracy of 98.15%, correctly classifying about 98% of genetically validated samples according to whether the homozygous SMN1 deletion was present or absent.
“This approach enables rapid and reliable identification of SMA patients with homozygous SMN1 deletion directly from whole blood samples and may serve as a practical first-line diagnostic tool for SMA,” the researchers wrote, adding that “the ability to determine SMN1 deletion status … within approximately one hour may be particularly valuable for rapid molecular testing in newborn screening programs and resource-limited laboratory settings.”
Leave a comment
Fill in the required fields to post. Your email address will not be published.