Patau syndrome is a very serious condition incompatible with life: most of those affected, in fact, die before birth or within the first week of life.
According to the most reliable research, it seems that Patau's syndrome is due to a "genetic aberration that takes place before conception and that concerns a sex cell of one of the parents or shortly after conception.
Generally, for the prenatal diagnosis of Patau syndrome, the following are necessary: prenatal ultrasound scans, one between bi-test or tri-test and amniocentesis or, alternatively, villocentesis.
Unfortunately, being the consequence of an irremediable genetic error, Patau syndrome is an incurable condition, even when detected at an early stage of fetal development.
- Each cell of a healthy human being has 23 pairs of homologous chromosomes, so 46 chromosomes in all (23 derive from the mother and 23 derive from the father); of these 23 pairs of homologous chromosomes, 22 are autosomal (the chromosomes that do not affect an individual's sex are autosomal) and one is sexual (the chromosomes that determine an individual's sex are sexual).
- In their totality, the 46 human chromosomes contain the entire genetic material, better known as DNA; the DNA of an individual is what establishes his somatic traits, predispositions, physical qualities, etc.
- DNA can undergo mutations, that is, alterations; these mutations can concern a DNA sequence inside one or more chromosomes (these sequences are called genes) or they can involve the number of chromosomes (we speak of trisomy, when there are 3 copies of the same chromosome, and of monosomy, when it is only one copy of a given chromosome is present).
The condition for which two copies of the same chromosome are present in the somatic cells of an organism - a condition that for the human being is equivalent to normality - is called diploidy.
Epidemiology
Patau syndrome is the third most common form of trisomy in the world, after Down syndrome (or trisomy 21) and Edwards syndrome (or trisomy 18).
Statistical data relating to the spread of trisomy 13 are somewhat discordant: according to some sources, the frequency of Patau syndrome calculated on the population of live born children would be equal to 1 case for every 5,000-12,000 births; according to other sources, however, it would be equivalent to 1 case every 16,000 births.
Patau syndrome seems to affect women more often than men; however, it should be noted that even the data relating to this epidemiological aspect are uncertain: some studies, in fact, report that trisomy 13 occurs in both sexes with the same frequency.
Origin of the name
Patau syndrome owes its name to Dr. Klaus Patau, who, in 1960, was the first to identify the association between the disease and the presence of an extra chromosome 13 inside the cells of the sick.
(in this case, however, it is in a moment after conception).
In Patau syndrome, the chromosomal error leading to the formation of a third chromosome 13 could take place before conception, during meiosis of the germ cells of one of the parents, or after conception, during mitosis of the fertilized egg.
In-depth study for the more experienced
According to the most accredited hypotheses, the chromosomal alteration that marks the Patau syndrome would consist in a phenomenon of non-separation (or non-disjunction) of the chromosomes in duplicate form (chromatids) destined, during the phases of meiosis and mitosis, to divide in the non-duplicated form within the daughter cells.
Genetic Mosaicism
As reiterated on more than one "occasion, Edwards syndrome is characterized by the presence of a third chromosome 18 in the constituent cells of the affected individual.
Genetic studies, however, have shown that the chromosomal makeup of about 10% of individuals affected by Patau syndrome is 47 chromosomes only for a part of the cells of the organism, while for the remaining part it is 46 chromosomes (therefore c "is also a normal chromosome set).
Also observable in other genetic diseases, this curious phenomenon - that is the presence in an organism of cells with distinct chromosome arrangements (one of which is normal and one pathological) - is called genetic mosaicism (or simply mosaicism).
The genetic mosaicism related to trisomy 13 is a phenomenon not yet fully understood; scientific studies in this regard suggest that it is observable only in sick subjects for whom chromosomal aberration takes place after conception, during the early stages of embryonic development.
It should be noted that, while remaining a condition incompatible with life, the Patau syndrome marked by genetic mosaicism is associated with a relatively less severe symptomatological picture than that observed when all the cells of the organism have 47 chromosomes.
In-depth study for the more experienced
In Patau syndrome, the degree of genetic mosaicism is variable: for some individuals, the number of cells with 47 chromosomes is lower than for others.
According to the researchers, this variability depends on when chromosomal aberration occurs in the mitosis phase: during embryonic development, the earlier the appearance of the third chromosome 13, the greater the number of possible cells with 47 chromosomes in the individual formed.
Translocation
Important scientific studies have found that, in a good 25% of cases of Patau syndrome, the third chromosome 13 is "attached", in whole or only in part, to another autosomal chromosome, rather than being "free" like the other two copies.
In genetics, this particular phenomenon, whereby a chromosome or part of it is attached to another chromosome, is known as a translocation.
In Patau's syndrome, although it is not so frequent, the translocation arouses considerable scientific interest, as it appears to be in all respects a hereditary phenomenon; the patients affected by the translocation, in fact, are generally children of couples, in which one of the two parents has, for one of the two chromosomes 13 present in his cells, the same type of translocation (NB: the parent involved is healthy, because his chromosome kit is always 46 chromosomes, even if one is attached to another).
In-depth study for the more experienced
The translocation of a chromosome has no health consequences, except when it concerns a chromosome present in triplicate or when, in the event, it involves the loss of genetic material from the chromosome concerned.
In genetics, when the translocation has no repercussions on the health of an individual, we speak of a balanced translocation.
Risk factors
Fertile women of any age can have a child with Patau syndrome; however, statistics show that they are more at risk in women over the age of 40.
of Patau syndrome consist of several external and internal physical abnormalities, including:- Small head (microcephaly).
- Holoprosencephaly. It is the failure to divide the brain into two hemispheres; it is associated with severe neurological problems and facial defects.
- Myelomeningocele (or spina bifida Aperto). It is the most severe form of spina bifida.
- Sloped forehead.
- Wide nose.
- Low and unusually shaped ears, associated with deafness and recurrent infections (otitis).
- Ocular defects of various kinds (microphthalmia, hypotelorism, anophthalmia, ocular coloboma and absence of the retina), associated with reduced or no visual abilities.
- Cleft lip and / or cleft palate.
- Polydactyly (or hyperdactyly) and camptodactyly. They are two malformations of the hands.
- Aplasia of the skin (or aplasia cutis). It is the medical term for lack of skin in certain areas of the scalp.
- In male individuals, cryptorchidism and malformations of the scrotum and genitals (eg: micropenis); in female individuals, on the other hand, bicornuate uterus and clitoral hypertrophy.
- Respiratory difficulties and cardiac defects (e.g. atrial and ventricular defects, patent ductus arteriosus, valvulopathies and dextrocardia).
- Kidney cysts.
- Gastrointestinal anomalies, such as omphalocele and abdominal hernia.
Symptoms and signs of Patau syndrome after one month of life
If the person with Patau syndrome reaches one month of life, they develop additional disorders, including:
- Difficulty eating properly;
- Constipation;
- Gastroesophageal reflux disease;
- Slow pace of growth;
- Scoliosis;
- Tendency to irritability;
- Sensitivity to sunlight (photophobia);
- Reduced muscle tone;
- Hypertension;
- Sinusitis and infections of the urinary tract, eye and ear.
If for various reasons it is not possible to carry out the aforementioned checks, the diagnosis of Patau syndrome occurs at birth, by means of an accurate physical examination and the chromosomal analysis of a blood sample.
Bi-Test
To be performed between the 11th and 14th week of pregnancy, it is an examination of screening which combines the measurement, by ultrasound, of nuchal translucency with the quantification, in maternal blood, of the PAPP-A proteins (plasma protein A associated with pregnancy) and hCG (chorionic gonadotropin).
The bi-test is a "diagnostic investigation useful to detect the possibility that the fetus has some chromosomal abnormality.
It presents a small margin of error, therefore, in the event that it provides suspicious results, it is necessary to resort to more in-depth examinations, such as amniocentesis or CVS.
Amniocentesis
Performable between the 16th and 18th week of pregnancy, amniocentesis consists in the transabdominal withdrawal of a small amount of amniotic fluid - that is the fluid that envelops and protects the fetus during its uterine development - and in the subsequent laboratory analysis of the chromosomal set of fetal cells contained in the sample of liquid taken.
Amniocentesis is a very thorough and reliable examination, which can identify any possible chromosomal abnormality; however, since it is associated with a minimal risk of fetal death, its execution is indicated only when prenatal ultrasound and bi-test or tri-tests give suspicious results or when particular conditions exist (eg advanced age of the mother, history of spontaneous abortions, etc.).
Villocentesis
Executable between the 10th and 12th week of pregnancy, CVS is a diagnostic technique similar to amniocentesis, with the only difference that the fetal material to be collected and subsequently analyzed in the laboratory are the chorionic villi (instead of the amniotic fluid).
Like amniocentesis, CVS can cause unwanted fetal death, so it is only indicated when strictly necessary.
.However, it should be noted that, for patients born alive, there is the possibility of subjecting them, clearly only after parental consent, to some symptomatic therapies with a purely palliative purpose.
Symptomatic-Palliative Treatments
Among the symptomatic-palliative treatments for those suffering from Patau syndrome, the following deserve a mention:
- Artificial feeding techniques, such as tube or gastrostomy;
- Surgery aimed at correcting the cleft lip and cleft palate;
- The use of visual and / or auditory aids to deal with any sight or hearing defects.
