A new muscle disease - myoglobin disease

A study published in Natural Communications reported a new muscle disease caused by a mutation in the myoglobin gene. The study was conducted by researchers at the Bellvitge Institute of Biomedical Research (IDIBELL).

The muscles are red because of myoglobin in the muscles. Myoglobin is a small cytoplasmic globular hemoglobin that is highly expressed in the heart and oxidized skeletal muscle fibers. Myoglobin is encoded by the myoglobin gene (MB) on human chromosome 22q12.3.

By reversibly binding oxygen, the intracellular buffered oxygen concentration of myoglobin promotes intracellular oxygen transport and acts as a reservoir during hypoxic and anoxic conditions of oxygen. In addition, myoglobin also scavenges free radicals and other reactive oxygen species, avoiding cell damage caused by oxidative stress.
Myoglobin is the first protein to determine the three-dimensional structure by X-ray crystallography. The backbone of myoglobin consists of eight alpha-helices surrounding a central pocket containing heme groups, which contain iron atoms that are usually in the center of the ferrous oxidation state. Its heme active site is responsible for the reversible binding of various ligands, including oxygen, carbon monoxide, and nitric oxide.

This is the first time that a disease caused by a mutation in the myoglobin gene has been discovered. And the researchers have found the same mutations in 14 members of six unrelated European families, all with the same symptoms, a very typical injury in muscle biopsy - called sarcoplasmic.

The sarcoplasmic body is the pathological marker of the disease and the main auxiliary means of diagnosis. They have some similarities to lipofuscin, also known as globular dense inclusions found in Pompe disease, but they are denser and more uniform and are often lacking in these two conditions to see vacuolar lipid droplets.

This new disease is named myoglobinopathy and is characterized by its onset during the fourth or fifth decade of life. It causes progressive weakness in the axial and limb muscles, and in the later stages, affects the respiratory muscle system and heart.

Infrared microscopy of the synchrotron MIRAS beamline characterizes the chemical composition and structure of the protein, enabling researchers to prove the presence of oxidized lipids in damaged muscle cells. And they have observed that sarcoplasmic bodies correspond to oxidized lipids and misfolded proteins.

Finally, researchers at the University of Modena and the University of Vienna discovered that the biochemical and thermodynamic properties of mutant myoglobin have changed, including a decrease in the affinity for molecular oxygen, which contributes to the formation of lipids and protein aggregates found in the muscles of patients.

This discovery has led to the establishment of a diagnosis of some patients many years later and has enabled researchers to focus on finding treatments for this disease from now on.
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