Zebrafish Model Offers Rapid Insights into SMA Genetic Variants for Newborns
A research team, led by Dr. Jean Giacomotto of Griffith University, has developed a method using zebrafish to quickly determine if specific genetic variants identified in newborns are likely to cause Spinal Muscular Atrophy (SMA). This innovative approach aims to provide timely information for clinical decisions, potentially preventing unnecessary treatments while ensuring critical interventions are not delayed.
This approach aims to provide timely information for clinical decisions, potentially preventing unnecessary treatments while ensuring critical interventions are not delayed.
Understanding Spinal Muscular Atrophy (SMA)
Spinal Muscular Atrophy (SMA) is a severe genetic disorder characterized by the progressive loss of motor neurons, leading to muscle weakness and impaired motor functions. It stands as a significant cause of infant mortality globally, with symptoms often including an inability to hold the head steady.
Crucially, effective therapies for SMA exist, but they are exceptionally costly, with some gene therapies exceeding $2 million per treatment. For these treatments to be most effective, they must be administered before the onset of symptoms, as any delay can result in irreversible degenerative damage.
The Clinical Dilemma: Variants of Uncertain Significance (VUS)
The expansion of newborn genomic screening programs has introduced a new challenge for clinicians: the increasing identification of 'variants of uncertain significance (VUS)' in genes such as SMN1, which is responsible for SMA.
When a baby carries a previously unobserved VUS, medical specialists face a profound dilemma:
Initiate expensive treatment immediately, risking an unnecessary intervention if the variant is benign, or wait for symptoms to appear, risking irreversible neurological damage if the variant is pathogenic.
This uncertainty places immense pressure on families and healthcare providers alike.
The Zebrafish Functional Assay: A Novel Solution
To address this critical challenge, Dr. Giacomotto's team at Griffith University’s Institute for Biomedicine and Glycomics developed a rapid, zebrafish-based functional assay. The research involved breeding zebrafish without the SMN1 gene, a genetic modification that typically results in a neuromuscular condition, degeneration, and early death in the fish.
The team then injected specific SMN1 gene variants from infants into these zebrafish embryos. The assay's design is straightforward yet powerful:
- The survival of the injected zebrafish indicates that the variant is not harmful and would not cause SMA.
- Conversely, a lack of survival would suggest pathogenicity.
This functional assay is designed to determine the pathogenicity of a novel SMN1 mutation within days.
Real-World Impact: Clinical Application and Success
The method has already demonstrated its utility in specific clinical scenarios. For instance, two infants – one in New South Wales, Australia, and another in Germany – both born in 2023, were identified through newborn screening as carrying previously unknown variants of the SMN1 gene.
Using the zebrafish model, Dr. Giacomotto's team functionally tested these specific variants. The results indicated that the variants were not harmful, providing critical clarity to clinicians.
This clarification was provided to clinicians within six weeks of the variants' identification.
As a direct result, these infants avoided potentially unnecessary medical treatments. They are now reported to be over two years old and developing normally. Professor Michelle Farrar, a paediatric neurologist involved in the research, highlighted the method's significant impact on clinical decision-making, particularly for uncertain results from newborn genomic screening programs.
Broader Implications and Future Potential
Researchers suggest that this zebrafish model could serve as a valuable tool for testing genetic variants of uncertain significance across a range of human diseases, significantly contributing to precision and personalized medicine.
Professor Peter Currie, director of research at the Australian Regenerative Medicine Institute, emphasized the suitability of zebrafish for this type of research:
Zebrafish share 70 percent of their genes with humans and their translucent embryos allow for easy observation of biological processes, making them a suitable model for studying human disease and screening experimental drugs.
The study indicates that zebrafish can play a pivotal role in clinical variant interpretation, especially as genomic sequencing becomes more widespread globally, leading to the identification of an increasing number of uncertain variants. This method offers a swift and cost-effective solution for resolving such complex cases.
The research, titled ‘Clinical relevance of zebrafish for gene variants testing: Proof-of-principle with SMN1/SMA,’ was published in EMBO Molecular Medicine.