Finding the ways in which changes in the genetic material (genotype) affects the structure and function of a given organism (phenotype) is the subject of very old attention, starting with the publication of the person who is considered the father of genetics, the priest Gregor Mendel (1822-1884). The year of the publication was 1866, so the inquiry is lasting for 151 years.
Human variation can be classified into two large groups, normal and pathological. The characteristic that was the subject of the article, hemophilia B (HB), is the less frequent (about 30%) of a clotting disorder that was recognized as a distinct pathology for many years now (the most frequent, around 70% of the cases, is hemophilia A, HA).
The familial character of the hemophiliacs, in general, was already recognized in the Talmud, the Jewish holy book, which dispensed babies from circumcision if the mother had relatives with hemorrhages; and its inheritance was clearly characterized by C. F. Nasse in 1820, therefore, four decades before Mendel’s publication.
Our research group has been interested in this pathology for more than half a century, and the beginning of the investigations was led by Israel Roisenberg (1934-2013). The present series of studies started with a 2009 paper, and the one which is being considered is the seventh. The series objective is the molecular characterization of the mutations responsible for the different clinical pictures of hemophilia patients, but we also investigated the factors that may influence the development of antibodies (inhibitors) against the substance used for the replacement of the missing or decreased factor. This complication, however, occurs only in HA patients, being very infrequent in HB.
Coagulation Factor IX, missing or decreased in HB, is synthesized in the hepatocytes as a precursor protein of 461 amino acids, and after appropriate processing presents four domains: GLA (gamma-carboxyglutamic acid), EGF-like (epidermal growth factor-like), and serine protease. The type of the mutation that is going to affect any one of these regions can also be classified whether: a) they affect only the processing of the protein (splicing sites); b) lead to coding errors (non-sense); c) to a different pattern in the processing and determination of the protein (frameshift); or d) to a different type of amino acid (missense). Depending on the type of mutation and the region of the protein that is going to be affected, different clinical patterns emerge.
We tested 43 Brazilian HB patients whose clinical conditions were classified as severe (30), moderate (7) or mild (6). A total of 31 types of mutations were detected in them, and all of them would lead to structural changes in the protein, such as spacing between units, incorrect folding or binding changes, as well as charge and hydrophobicity modifications. Their position (namely, near or distant from sites of interaction with other coagulation factors) is also important.
Six of the 31 mutations had not been previously described in the literature, and detailed molecular information about them, as well as models for the interpretation of the four new missense mutations found (comparing the normal and mutant proteins), were provided.
So far, so good. However, what is the importance of these findings for the patients themselves, their families, or science in general?
The answers are as follows: a) Improved diagnosis: the finer subdivisions obtained would allow a better comparison between patients with the same mutation in terms of clinical severity and of prospects for the future; b) Improved genetic counseling: the determination of the exact change would allow a more precise and cheaper search for the presence or not of the allele in female potential carriers; and c) Gene therapy: with the progress in the techniques of gene editing, it will be possible, in the future, to correct the specific change which occurred with gene therapy methods, leading to the patient’s cure.
This study, Molecular characterization of haemophilia B patients in southern Brazil was recently published in the journal Haemophilia.