If you are asked to show where your heart is located, without hesitation, you put your hand… at the top left of your chest. But did you know, in some people, the heart muscle is located on the right side?
Going to the doctor and learning that your heart is at the top right of your chest, not at the left as is not the case for the vast majority of us. But for very few of us, it’s a reality. Described for the first time in 1643, this phenomenon even bears a name, “situs inversus”.
Situs inversus is a disease characterized by abnormal placement of the thoracic and/or abdominal organs. It is an inversion of these parts of the body compared to normal. This pathology can develop in isolation (without other underlying conditions) or may appear in addition to other deficiencies, abnormalities and pathologies. In addition, congenital heart defects are present in 5 to 10% of cases of the disease.
Situs inversus is a complex and rare disease whose mode of transmission is genetic and hereditary.
The vital or long-term prognosis of patients with situs inversus depends directly on whether or not this pathology is associated with other abnormalities, particularly with cardiac deficiencies. Patients with the disease without underlying problems have an excellent prognosis. Conversely, when situs inversus is associated with other conditions or other pathologies, the prognosis also depends on these underlying causes and may therefore be less favorable.
The diagnosis of the disease can be made before the birth of the child during ultrasounds or MRI (Magnetic Resonance Imaging), which can provide additional information about fetal development, the progress of the disease and possibly the prognosis. Postnatal exams provide a broader perspective and confirm prenatal diagnosis. These tests include genetic tests.
The knowledge of the overall health of people with this pathology is important in the diagnosis of underlying medical problems as well as to prevent possible complications.
In the context of the development of situs inversus without the presence of any other underlying anomaly, which could be the cause, the symptoms relate to a completely reversed image of the thoracic and abdominal disposition.
Many people with associated diseases, Kartagener syndrome or even primary ciliary dyskinesia, clinical manifestations result in the symmetrically inverted placement of thoracic and abdominal organs added to the symptoms associated with the underlying conditions.
The severity of malformations varies from one patient to another. This can range from cardiac, kidney, biliary malformations and so on.
Aplasia, an undeveloped or absent spleen, as well as polyspenia, the presence of several small spleens with abnormality of lateralization, are also possible in the context of the disease.
Transmission of the disease is inherited genetically. Nevertheless, the transfer is complex. Several familial cases have been identified in which hereditary processes have been described.
The most common mode of transmission of the disease is autosomal recessive. That is, that the mutated gene of interest is located on a non-sexual chromosome and the presence of both copies of the mutated gene is indispensable in the development of the disease.
Other modes of hereditary transfer have also been highlighted:
the dominant autosomal transfer: the mutated gene is located on a non-sexual chromosome and the presence of only one of the two copies of the mutated gene is sufficient for the subject to develop the disease phenotype;
X-linked transfer: the mutated gene is located on an X sex chromosome.
The transmission of the disease is heterogeneously effective, which means that genetic factors or genes can interfere with the risk of mutations in different people.
The risk factors for developing the disease are genetic.
Indeed, different modes of transmission have been shown in the development of the disease.
In the context of an autosomal recessive transfer (for the majority of cases), a single copy of the mutated gene is not sufficient for the individual to develop the disease. It is essential for the subject to receive the mutated gene from both parents to develop the disease phenotype. In this case, if the associated risk factor is the presence of the disease in both parents.
Regarding the autosomal dominant transfer, this time, the presence of only one of the two copies of the mutated gene is sufficient for the individual to be sick. In this sense, the risk factor is that a subject has one of both parents with the disease.
Finally, X-linked transmission consists in the fact that the mutated gene is positioned on the sex chromosome X. Girls with a XX sex genetic inheritance and XY for boys, so girls have higher risk.