An international team of researchers have identified a gene that, when altered, can cause bent fingers and toes, clubfoot, scoliosis, and short stature.
Partial loss of the protein coding gene MYLPF (myosin light chain, phosphorylatable, fast skeletal muscle) results in a disorder called distal arthrogryposis (DA) that’s present at birth, according to the researchers, in The American Journal of Human Genetics.
The discovery has several exciting implications, notes Jared Talbot, an assistant professor in the University of Maine School of Biology and Ecology, and Jessica Chong, an assistant professor of human genetics at the University of Washington, in a media release from University of Maine.
“Before a disease can be effectively treated, its cause needs to be understood. Right now, DA is treated through surgery, which often has to be repeated several times over a lifetime. By understanding the disease better, we may be able to discover longer-lasting and less-invasive ways to treat it.”
— Jared Talbot
More broadly, the breakthrough adds to scientists’ knowledge about how prenatal muscle formation affects health throughout a lifetime, he adds.
MYLPF Mutations ID’d in 19 People with DA
Chong began the project while working with Dr. Michael J. Bamshad in the University of Washington’s Division of Genetic Medicine. They identified the initial cases and headed an international team that, so far, has identified MYLPF mutations in 19 people with DA in eight families.
Their results also could provide insight into arthrogryposes, which occurs in about 1 in 3,000 births. Arthrogryposes are a larger group of conditions characterized by multiple joint contractures at birth, including in the shoulders, hips and knees. The most common type of arthrogryposis is amyoplasia, which involves muscle loss.
“We hope that our findings may help to shed light on potential genetic causes of amyoplasia, because to date, the etiology of most cases of amyoplasia remains unknown.”
— Jessica Chong
Chong and Bamshad also learned of a person with DA who had no muscle in one of their feet, which indicates there may be more similarity than previously thought between DA and amyoplasia.
Bamshad and Chong contacted Talbot, who studies the same gene in zebrafish embryos.
Zebrafish have a similar genetic structure to humans. They share 70% of genes with people, and 84% of genes known to be associated with human disease have a zebrafish counterpart. Zebrafish muscle development also mirrors that of people and their embryos grow quickly and are see-through.
Talbot investigated how muscle development is affected by loss of this gene’s function, to understand the “why” behind the human findings. He began work on MYLPF while a postdoc in Dr. Sharon Amacher’s laboratory at The Ohio State University.
There, he mentored Emily Teets, who studied MYLPF function as part of her undergraduate honors thesis. They generated mutations that remove one of the two zebrafish MYLPF genes, called mylpfa, and found that this gene is needed for normal muscle structure and function.
Last fall, Talbot began research at UMaine, where he uses zebrafish to investigate muscle formation and model this human muscle disease.
“MYLPF protein acts in the muscle. We think the crooked joints of DA arise because of reduced muscle function when those joints are forming in the womb. We can’t study people’s muscle strength before they’re born, but we can study zebrafish in their early development and use these fish to model what happens in people.”
— Jared Talbot
Talbot found that zebrafish with mylpfa knocked out had complete paralysis in their pectoral fin and reduced overall muscle strength.
Degeneration in Utero May Lead to Muscle Loss
In addition, he and Teets discovered that muscle eventually degenerated in the zebrafish. This, he says, suggests that some muscle loss that people with DA experience may be due to degeneration in utero.
Talbot used protein models to understand why some of the specific mutations found in humans have dominant inheritance (where one copy of a mutation can cause disease) and other mutations have recessive inheritance, (where two copies must be mutated for a disease to occur).
He found the dominant mutations are caused by changes in parts of the protein that directly contact another protein called myosin, which is the motor protein that contracts muscle.
And, working with David Warshaw at the University of Vermont, they showed that myosin function is reduced in the zebrafish DA model.
Together, these fish and human findings show that MYLPF mutations cause a disease, DA, and they offer insights into how and why that disease arises before birth.
“I have investigated several disease models, but this was the first time that I was able to offer insights from a model organism at the same time that the gene’s function was being connected to a human condition. Our basic-science study paired beautifully with the clinical findings to tell one cohesive story that was enriched by everyone involved.”
— Jared Talbot
[Source(s): University of Maine, EurekAlert]
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