Hereditary primary hemochromatosis is one of the most common metabolic inborn errors in Europe. The body is overloaded with iron in this disorder, also known as iron storage disease. Excess iron accumulates in organs and tissues, causing gradual damage to the liver, heart, pancreas, pituitary gland, and joints. This can result in heart muscle changes (cardiomyopathies), diabetes mellitus (bronchial diabetes), and even scarring of the liver tissue (liver cirrhosis) and liver cancer.
|Professor Dr. Michael Ott, Dr. Simon Krooss, and first author Dr. Alice Rovai (from left). Photographer: Karin Kaiser / MHH|
The cause is a genetic defect that disrupts the regulation of iron absorption via the small intestine's mucous membrane. A research team led by Professor Dr. Michael Ott and Dr. Simon Krooss from the Hannover Medical School's Department of Gastroenterology, Hepatology, and Endocrinology has discovered a way to treat hereditary diseases using targeted gene correction. The findings were published in Nature Communications.
Defective iron absorption control
"In most cases, iron storage disease is caused by a mutation in the hemochromatosis gene HFE, which is found on chromosome 6," Professor Ott explains. It only occurs in people who inherited the defect from both parents, i.e. who lack a "healthy" gene to compensate. A specific change known as the C282Y mutation is found in both copies of the HFE gene in more than 80% of those affected. This results in the substitution of an amino acid—a protein building block—in the HFE protein.
As a result, the HFE protein no longer controls iron absorption into intestinal cells. Patients must accept lifelong phlebotomies in order to empty the iron stores and normalize the iron concentration in the body. "This is stressful, and it does not work for everyone," says the hepatologist. Drugs that bind the iron directly in the body and thus neutralize it are also unsuitable due to severe side effects.
The cell begins the repair process.
As a result, the MHH researchers are taking a different approach. They repair the defective HFE gene using the body's own repair mechanisms. They specifically altered a tiny faulty building block in the mutated HFE gene using CRISPR/Cas technology, also known as "gene scissors," and an accompanying biotechnological tool.
The procedure is known as base editing in technical parlance. The gene scissors were used in such a way that they did not simply cut the DNA double-strand completely at the desired position, as in the traditional application. "There is always a risk of unwanted mutations with double-strand breaks," says the doctor and scientist. In contrast, with base editing, the two single strands are separated and only one of them is altered.
"As a result, the cell automatically initiates its natural repair program and incorporates the correct nucleotide in the second strand as well, resulting in the C282Y mutation disappearing in the entire double strand," Dr. Krooss explains.
Iron levels in the blood of mice are significantly reduced.
This biotechnological trick was investigated in the mouse model by the research team. The rate of gene correction with a single injection was 12%. "This is a huge success because most genetic diseases can already be controlled if 5% of the cells have the correct gene," says first author Dr. Alice Rovai. Four months after the intervention, the iron levels in the blood had already dropped significantly. Furthermore, the researchers anticipate a further reduction in iron levels after twelve months. "Because the repair system is slow, it takes time for more liver cells to correct the gene."
However, the research team is looking for more. So far, they have packaged the CRISPR/Cas system with the molecular tool in a viral vector, also known as a gene taxi, and injected it into mice. The researchers plan to send only the mRNA blueprint for the base editing system in the next step, similar to the mRNA vaccines against the SARS-CoV-2 coronavirus.
"This is safer and more efficient because we can avoid using the viral vector, potentially increasing the success rate to 30 to 40%," says Dr. Krooss. If this is successful and the application is then tested in humans, a single injection could one day save people suffering from hemochromatosis who are suffering from liver cancer and organ removal.
"Injection rather than transplantation," says Ott, a liver researcher. Furthermore, base editing may be a therapeutic option for many congenital diseases caused by a single defective gene.
Journal information: Nature Communications