This novel hemoglobin variant, caused by a duplication of 23 amino acids in the hemoglobin (HBB) gene, leads to protein instability, triggering episodes of acute hemolytic anaemia, particularly during febrile episodes. The discovery, published in the journal Med by Cell Press, opens new avenues for studying these rare conditions with the aid of artificial intelligence.
The clinical case leading to the discovery involved a young Chinese girl who developed severe hemolytic anaemia after a febrile episode. This condition is characterised by the accelerated destruction of red blood cells at a rate that outpaces the bone marrow's ability to produce them. In children, acute episodes can significantly impact their overall health.
"Certain hemoglobin variants, known as ‘unstable hemoglobins,’ degrade under physical stress, such as fever, triggering hemolytic crises. These are generally caused by single-point alterations in the amino acid sequence of hemoglobin, affecting the protein's stability and functionality," explains Carlo Gambacorti-Passerini, Director of Haematology at the IRCCS San Gerardo dei Tintori Foundation and Professor at the University of Milano-Bicocca, who coordinated the research.
The young patient was under the care of Dr Paola Corti and technician Amedeo Messina at the San Gerardo dei Tintori Foundation. They identified that the anaemia stemmed from an unstable hemoglobin variant. Genetic analysis revealed that the patient’s mother and two siblings also carried the same variant and experienced similar episodes during fevers. Subsequent investigations showed that this hemoglobin variant was not only novel but characterised by an unprecedented long duplication of 23 amino acids in the beta chain of hemoglobin (HBB)—a feature never observed in other unstable hemoglobins.
Long duplications in the HBB gene are exceedingly rare and have historically been associated with beta-thalassemia. It has been assumed that such duplications disrupt the interaction between the beta and alpha chains of hemoglobin. Dr Ivan Civettini, a haematologist now pursuing a doctorate at the IRCCS San Raffaele Hospital, and Dr Arianna Zappaterra, a physician at the San Gerardo dei Tintori Foundation’s Haematology Division, investigated how such a significant mutation could allow hemoglobin to retain normal functionality under physiological conditions.
"The hemoglobin variant's structure was modelled using 3D techniques and artificial intelligence (neural networks), methods recently awarded the Nobel Prize in Chemistry," notes Dr Civettini. "Under normal conditions, the bond between the two hemoglobin chains is preserved, and the duplication manifests as a long protrusion flapping outside the protein structure. This mutation does not affect hemoglobin's active centre, where oxygen and iron bind. Essentially, under normal conditions, Hemoglobin Monza remains stable, and its chain interactions do not result in beta-thalassemia."
What happens during febrile episodes? Advanced computational techniques, such as molecular dynamics, were used to simulate these conditions. A fluid replicating human blood's salinity was prepared, containing both normal hemoglobin and Hemoglobin Monza, and heated to 38°C to mimic a fever. The results showed that Hemoglobin Monza degrades faster than normal hemoglobin, losing its bond with the iron atom. These experiments were conducted in collaboration with Professor Alfonso Zambon of the University of Modena and Reggio Emilia.
"The discovery provides valuable insights into rare hemoglobin variants, which will likely become more common in Italy due to the increasing diversity of the population," adds Professor Gambacorti-Passerini. "The use of modern computational techniques and artificial intelligence has made such studies faster and more cost-effective compared to traditional methods like X-ray crystallography. This is yet another demonstration of the importance of interdisciplinary collaboration in modern medicine."
Included are 3D models of Hemoglobin Monza.