Generality
Agenesis is the medical term that describes the complete absence of an organ, due to an incorrect embryonic development.
Episodes of agenesis, therefore, are anatomical anomalies of a congenital nature.
Agenesis should not be confused with aplasia: while in the case of agenesis, the affected organ is completely absent, in the case of aplasia the affected organ is minimally sketched.
Definition of agenesis
Agenesis is the term that, in medicine, indicates the "complete absence of an organ, following an error during embryonic development
An "agenesis is, in fact, a" congenital anatomical anomaly, where for "congenital" s "means" present from birth ".
Numerous organs of the human body can be the object of agenesis.
ARE AGENESIA AND APLASIA SYNONYMOUS?
Although it is a fairly widespread trend, equating agenesis with aplasia is a mistake.
In fact, while agenesis is the complete absence of an organ, the term aplasia indicates the lack of development of an organ or tissue, where for "lack of development" s "means" development not completed ".
In essence, therefore, if in the first situation (agenesis) there is not even a sketch of the organ concerned, in the second situation an attempt - albeit minimal - to develop the organ involved exists and is sometimes even visible.
ORIGIN OF THE NAME
The term "agenesis" derives from the "union of two Greek words, which are: the so-called privative alpha, corresponding to the initial letter" a, "and" genesis "(γενεσις). The" privative alpha denotes a lack, while "genesis" it means "birth" or "generation".
Therefore, the meaning of agenesis is "lack of generation".
Types
There are various types of agenesis. The criterion of distinction for the various typologies is, as can be understood, the organ concerned.
The most common types of agenesis include: renal agenesis, penile agenesis, testicular agenesis, corpus callosum agenesis, Müllerian agenesis, uterine agenesis and phocomelia.
On the other hand, the less common types of agenesis include: gallbladder agenesis, ocular agenesis, ear agenesis and dental-oral agenesis.
RENAL AGENESIA
Renal agenesis is a congenital anatomical anomaly characterized by the lack of one or both kidneys from birth. Specifically, the lack of only one kidney is called unilateral renal agenesis, while the lack of both kidneys is better known as bilateral renal agenesis.
Renal agenesis in its unilateral form is decidedly more widespread than renal agenesis in its bilateral form; according to reliable statistical surveys, in fact, the first would involve a new born every 500, while the second would concern a new born every 4,000.
For unknown reasons, the lack of one or both kidneys from birth (congenital deficiency) is more common in the male population.
Renal agenesis can be an isolated condition or a condition associated with pathological states, such as: trisomy 21, trisomy 22, trisomy 7, trisomy 10 or Turner syndrome.
The symptomatological picture of renal agenesis is variable: the absence of only one kidney is an asymptomatic condition, as long as the only kidney present is healthy; on the contrary, the lack of both kidneys entails, starting from fetal life, the presence of a condition known as oligohydramnios, which can lead to other malformations and, in severe cases, death at birth.
Anatomical malformations that may be associated with unilateral renal agenesis:
- Potter's Syndrome;
- Poland syndrome;
- Anomalies of the Müllerian ducts;
- Seminal vesicle cysts;
- Congenital cardiac anomalies;
- Sirenomelia
PENALTY AGENESIA
Penile agenesis is a congenital anatomical anomaly, which exclusively affects the male population, characterized by the lack of a penis.
With an incidence equal to one case every 5-6 million new male births, penile agenesis can occur in isolation or associated with testicular agenesis (which will be discussed later).
The main problem of males who are born with penile agenesis is the inability to eliminate urine. To remedy this problem, patients must undergo a specific surgery, aimed at creating a functional urethra.
TESTICULAR AGENESIA
Testicular agenesis is the medical term that indicates a "congenital anatomical anomaly, exclusive to the male population, which is characterized by the lack of testicles.
According to reliable studies, testicular agenesis would arise as a result of the failure, during embryonic development, of some particular cells, called Leydig cells.
The lack of testicles has various repercussions on the functionality of the reproductive system of the male concerned: from the lack / absence of testosterone to the absence of spermatozoa and to the non-existent development of secondary sexual characteristics.
AGENESIA OF THE CALLOUS BODY
The agenesis of the corpus callosum is a congenital anatomical defect, characterized by the absence of the so-called corpus callosum. The corpus callosum is the lamina of white matter, with a sagittal course and curved shape, which is interposed between the two cerebral hemispheres and is made up of myelinated nerve fibers.
The agenesis of the corpus callosum depends on an error during the fetal development of the brain, the latter process which takes place between the third and the twelfth week of gestation.
The causes of the aforementioned error are still uncertain. According to the most reliable hypotheses, they could consist of: chromosomal aberrations, genetic-hereditary mutations, prenatal infections or trauma to the head, prenatal exposures to toxins, prenatal brain cysts or metabolic diseases.
The agenesis of the corpus callosum can cause various symptoms and clinical signs, including: visual difficulties, hypotonia, reduced motor coordination, slowing of movements, reduced perception of pain, difficulty in chewing and swallowing, cognitive deficits, epilepsy attacks, spasticity , hearing problems, cranial malformations etc.
At the present time, there are no specific treatments for the agenesis of the corpus callosum, but only support treatments, aimed at improving the symptomatological picture.
- Aicardi syndrome;
- Shapiro syndrome;
- Acrocallosal syndrome;
- Septo-optic dysplasia (or de Morsier syndrome);
- Mowet-Wilson syndrome;
- Menkes syndrome.
Figure: the corpus callosum in the brain of the human being.
MULLERIAN AGENESIA AND UTERINE AGENESIA
Exclusive to the female population, Müllerian agenesis and uterine agenesis are two particular anatomical anomalies of a congenital nature, which are characterized, respectively, by the absence of the uterus, combined with more or less severe malformations of the proximal portion of the vagina, and for the sole absence of the uterus.
In other words, while women with Müllerian agenesis lack a uterus and have an abnormal vagina, women with uterine agenesis only have no uterus.
Both Müllerian agenesis and uterine agenesis are responsible for a condition of primary amenorrhea, in which the levels of sex hormones are normal due to the presence of functional gonads.
Sometimes associated with renal agenesis or vertebrae abnormalities, Müllerian agenesis and uterine agenesis are two examples of Müllerian duct anomalies; to be precise, they are anomalies of class I Müllerian ducts.
FOCOMELIA
Phocomelia is a very rare genetic disease that causes congenital anatomical anomalies of varying severity in the limbs, head and / or internal organs.
Phocomelia is included in the list of forms of agenesis, since, among the possible anatomical anomalies dependent on it, there are also the lack of upper or lower limbs and the lack of lungs.
AGENESIA OF THE gall bladder
Agenesis of the gallbladder is a congenital anatomical anomaly, which is characterized by the absence of the gallbladder.
Very often asymptomatic, this particular condition is very rare indeed; according to some statistical studies, in fact, it would have an "incidence on the general population equal to less than 0.1%.
OCULAR AGENESIA
Ocular agenesis is a congenital anatomical anomaly characterized by the absence of the eyeballs.
AGENESIA OF THE EARS
The "agenesis of the ears is a" congenital anatomical anomaly, which can be characterized by the absence of all the components of the ears (from the external ear to the internal ear) or by the absence of only the external portion (inner ear).
While people who lack all components of the ears are completely deaf, people who lack only the outer ear still have some degree of hearing ability.
DENTAL-ORAL AGENESIA
Dental-oral agenesis is a group of malformations, characterized by the lack of elements that make up the mouth.
Among the various dental-oral agenesis, the following deserve a mention: anodontia, aglossia and agnatia.
Anodontia is the agenesis of the teeth; this particular condition can affect both primary and secondary dentition.
Aglossia is the agenesis of the language; therefore the stakeholders do not present the language.
Finally, agnathy is the agenesis of the mandibular bone or mandible.
