For more information about the composition and biological role of blood, about the essence of anemia, see the material “Anemia. Blood and bloodlessness” .
Sickle cell anemia is a severe hereditary disease, also known as drepanocytosis, meniscocytosis, S-hemoglobin disease, Herrick’s syndrome, African hemolytic anemia (hemolytic – Greek literal “dissolving, decomposing blood”). The modern history of the study of this type of anemia began, as it is believed, in the middle of the 19th century , when the spleen was not found in the body of an African slave executed for escaping. Then , in 1910, a report appeared written by a professor of cardiology, James B. Herrick , and his intern , Ernest E. Irons.. In a blood test of a 20-year-old student who had been treated since 1904 for “anemia, muscular rheumatism, and biliary overflow” (he died of pneumonia in 1916), Irons observed and first described red blood cells of a strange shape, which he defined as “elongated and sickle-shaped “. The name “sickle cell anemia” was first used as a diagnosis by Verne Mason in 1922 . Since the 1930s , epidemiological studies on this disease began in samples of children of African descent.
It can be assumed that the genetic mutation leading to sickle cell anemia appeared on the African continent – and was fixed in the population, oddly enough, as a useful trait: gene carriers and patients with this form of anemia show relative resistance to malaria . The malarial plasmodium parasitizes and destroys red blood cells, but erythrocytes, genetically mutilated and carrying a completely different hemoglobin (see below), are “inedible” for plasmodium. And although the anemia of malaria is not sweeter, the lethality of swamp fever is still higher: those who had at least some immunity survived.
In an actively migrating humanity that is becoming increasingly international and gradually interracial, sickle cell anemia is ubiquitous. However, a certain endemicity persists today: in Equatorial Africa, the Mediterranean basin, India, the Middle East, the frequency of genetic carriage (not to be confused with the incidence in clinical form) reaches 40%.
According to a special study conducted in 2001 in Jamaica, the average life expectancy of patients with homozygous sickle cell anemia is 53 years for men and 58 years for women. About 90% live up to 20 years, about half live up to 50 years.
In other words, the problem is very serious, it is characterized by high medical and social significance and needs effective solutions, which are currently being sought by leading specialized research centers. The prevalence of hereditary hemoglobinopathies (including sickle cell anemia) in the world is estimated at 3-7%. In the early 2010s, WHO classified sickle cell anemia as a global health problem.
The epidemiological situation and mortality rates in third world countries are unknown or not sufficiently reliable.
According to the literature, due to migration processes, the incidence in Russia shows a significant and steady upward trend, especially in Moscow and St. Petersburg.
The reasons
S-hemoglobin (from the English “a sickle” – sickle), encoded by a faulty gene, is much more viscous and about a hundred times less soluble than normal A-hemoglobin; in addition, the ability to bind oxygen and transport it to the tissues is many times lower, which is what causes the actual anemic symptoms of hypoxia. Erythrocytes containing altered hemoglobin differ in the shape of an elongated deformed crescent or crescent from normal blood cells, which look like a relatively thick biconcave disc. The unnatural shape and rigidity of S-erythrocytes causes a tendency for them to clog capillary beds. Hemolysis is sharply accelerated, i.e. the life span of S-erythrocytes is much shorter than that of normal red cells.
The patient’s blood may contain both normal and abnormal red blood cells, or only abnormal ones. Obviously, in the second case, the disease is much more severe and the prognosis is worse; the first option may be little or even asymptomatic.
The type of inheritance is autosomal recessive. This means that two parents who carry the gene have a 50% chance of having a child with the same gene, and a 25% chance of having a child with a clinical form of sickle cell anemia. If only one of the parents is a carrier, the probability of inheriting the gene remains fifty percent, but the disease itself does not manifest in the child.
Symptoms
Like most genetic diseases, sickle cell anemia is characterized by an extraordinary variety of possible symptoms, syndromes, and complications. Their variability is so great that no clinical picture and no individual case can be considered typical.
The debut in most cases falls on early childhood, and then three periods can be traced in the development of the disease.
In the initial period , as a rule, the symptoms of microthrombosis, osteoarticular pains and pains of other localization, swelling of the joints, enlargement of the spleen, jaundice (due to the accelerated breakdown of hemoglobin) dominate. Such children are highly prone to infections, including osteomyelitis. The course of the disease at this stage is often of a crisis nature and is easily aggravated under any adverse conditions. For example, a hemolytic type crisis is often provoked by an infection and can be fatal; aplastic, sequestration, vascular (thrombotic) crises are also life-threatening syndromes.
In many cases, there is a characteristic deformation of the structures of the musculoskeletal system and bones of the skull: kyphosis, lordosis, acrocephaly (“tower skull”), as well as serious delays in psychophysical development.
At the second stage , an abnormally intense production of erythrocytes can be observed as a compensation for their failure. Due to thrombosis, heart or kidney failure, strokes, diabetes mellitus, cirrhosis of the liver, and trophic leg ulcers often develop. Most patients with such a severe picture of the second period die within a few years.
The third period, if it occurs at all, is characterized by moderate hemolytic symptoms. The absence of the spleen (see above) is due to the phenomenon of shrinkage and self-destruction (autosplenectomy) after repeated infarcts. The liver remains enlarged, there is a high predisposition to the purulent-inflammatory course of any infectious diseases.
Optional (possible in different cases, but not mandatory) complications of sickle cell anemia are cholelithiasis, aseptic bone necrosis (avascular osteonecrosis), immunodeficiency, priapism in men, preeclampsia and miscarriages in pregnant women, intrauterine growth retardation, acute renal necrosis, retinopathy (retinal detachment can result in complete blindness), pulmonary hypertension, and many others.
More or less prolonged attacks of acute pain in the bones, joints and muscles are characteristic. The National Health Service of Great Britain has included sickle cell anemia in the list of the most painful conditions .
Diagnostics
The diagnosis is established by a characteristic combination of symptoms common to anemia and specific manifestations. A thorough multifactorial laboratory blood test is performed . Medical genetic testing is scheduled.
Treatment
To date, there is only palliative, symptomatic treatment , which in many cases requires the participation of several specialized specialists. Of great importance is the prevention of infectious diseases, good nutrition, control of sufficient intake of vitamins (especially B9 and B12).
It should be noted that in March 2017, The New England Journal of Medicine published an article in which a large team of authors reported the first ever case of significant alleviation of sickle cell anemia by genetic engineering. A French teenager received such treatment at the Necker University Hospital (Paris), known since 1802 as the world’s first specialized medical facility for children.
However, the prognosis of the further development and course of the disease, as well as the prospects for introducing the method into clinical practice, are still unclear. I would like to hope that this success is certainly outstanding! – will mark a long-awaited and much-needed revolution in the treatment of sickle cell anemia and, in general, chromosomal diseases.
