The Chromosomal syndromes Are the result of anomalous genetic mutations that occur within the chromosomes during the formation of the gametes or in the first divisions of the zygote.
The following is a list of 14 types of chromosomal syndromes and their causes , With emphasis on how genetic alteration occurs.
Types chromosomal syndromes
1- Turner syndrome or monosomy X
He Turner's syndrome A genetic pathology associated with the female sex that occurs as a consequence of the partial or total absence of an X chromosome, in all or part of the Cells Of the agency (National Organization for Rare Disorders, 2012).
The karyotype of Turner syndrome has 45 chromosomes, with a model of 45 X and a missing sex chromosome.
2- Patau's syndrome
He Patau's syndrome Is the third most common autosomal trisomy after Down syndrome and Edwards syndrome.
In the case of this syndrome the genetic anomaly specifically affects the chromosome 13, that is to say that it has three copies of the same chromosome.
3 - Down Syndrome or Trisomy 21
The known Down Syndrome or Trisomy 21 Is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is the most frequent chromosomal syndrome of congenital psychic cognitive disability.
The causes of chromosomal excess are still unknown, although it is statistically related to maternal age above 35 years.
Edward's Syndrome
He Edward Syndrome or Trisomy 18 is a Aneuploidy Which is characterized by the presence of an additional complete chromosome in pair 18.
This may also be due to the partial presence of chromosome 18 due to a translocation of deceleration or mosacism in the fetal cells.
5- Fragile X syndrome
He Fragile X syndrome , Is a genetic disorder that is due to the mutation of a gene, which is inactive and can not perform the function of synthesizing this protein.
Although it is one of the most frequent hereditary disorders, it is quite unknown for the general population, so its diagnosis is usually wrong and late.
Usually affects males, since in women having two X chroms, the second protects them.
6- Cri's syndrome Du chat o 5 p
He Cri du Chat syndrome , Also known by the cat's meow syndrome, is one of the chromosomal disorders produced by a Deletion At the end of the short arm of chromosome 5.
It affects one in every 20,000-50,000 newborns and is characterized by the crying that these babies usually have, resembling the meow of a cat, hence its name.
Usually, most of these cases are not inherited, but it is during the formation of the reproductive cells when genetic material is lost.
7- Wolf Hirschhorn Syndrome
He S Wolf Hirschhorn syndrome , Also called Dillan 4 p monochromosomal deletion syndrome, is characterized by multisystemic involvement, leading to severe mental and growth disorders.
A good part of the affected people die during the prenatal or neonatal phase, but some with a moderate affectation can arrive to exceed the year of life.
8- Klinefelter syndrome or 47 XXY.
East syndrome Is due to a chromosomal anomaly that consists of the existence of two XX plus chromosomes and one Y chromosome. It affects the men and it causes Hypogonadism , Ie the testicles do not function properly, which leads to various malformations and metabolic problems.
Such aneuploidies on sex chromosomes are usually relatively frequent.
Normally, in the middle of the occasions it is due to paternal meiosis I, and the rest of occasions to maternal type II meiosis.
9- Robinow's syndrome
He Robinow's syndrome Is an extremely rare genetic disorder characterized by dwarfism and bone malformations.
Two types of Robinow syndrome have been identified, distinguished by the severity of their signs and symptoms and by inheritance patterns: the autosomal recessive form and the autosomal dominant form.
Recessive autosomal inheritance means that both copies of the gene in each cell must have the mutations for the alteration to be expressed. The parents of a subject suffering from this recessive disease have a copy of the mutated gene but they do not show any signs or symptoms of the disease.
In contrast, autosomal dominant inheritance means that a copy of the altered gene in each cell is sufficient to express the alteration.
10- Double Y syndrome, XYY
AND L Double Y syndrome, Or commonly called superman syndrome, is a genetic disease caused by a chromosomal excess.
As you can see from an alteration in the Y chromosome, it only affects males.
Although it is due to an anomaly in the sexual chromosomes, it is not a serious disease, since it does not have alterations neither in the sexual organs nor problems in the puberty.
11- Prader syndrome WILLI
He Prader Willi Syndrome , Is a non-hereditary and rare congenital disorder. In those people suffering from SPW there is a loss or inactivation of the genes of the 15q11-q13 region of the long arm of chromosome 15 inherited from the father.
Among the symptoms we have Muscle hypotonia And feeding problems in your first stage ( Hyperphagia And obesity) from the two years with somewhat peculiar physical features.
12- Pallister Killian Syndrome
The Killian Pallister Syndrome , This syndrome occurs due to the anomalous presence of an extra chromosome 12 in some cells of the organism, giving rise to diverse muscoloskeletal anomalies in neck, limbs, spine, etc.
13- Waardenburg syndrome
He Waaedenburg's Syndrome , Is a disease of the autosomal dominant type with different ocular and systemic manifestations.
It is considered an auditory-pigmentary syndrome, characterized by alterations in the pigmentation of the hair, changes in the coloration of the iris and sensorial loss of the hearing of moderate to severe.
14- William's Syndrome
He William syndrome Is characterized by the loss of genetic material on chromosome 7, also called Monosomy .
This pathology is characterized by atypical facial alterations, cardiovascular problems, cognitive delay, learning problems, etc.
The causes of chromosomal syndromes: a Chromosomal abnormalities
As you will know, most species have two copies of each chromosome, one for each parent, so when it is altered, we find various anomalies in both number and structure.
Changes in chromosome number
All our cells are diploid, which means that the number of chromosomes is even.
The diploidia assumes that for each chromosome that exists there is another equal, therefore we have two copies of each gene, each in its corresponding place of each chromosome.
When forming an embryo, each of the members provides a chromosome, either X for the female sex or Y for the male sex.
The important thing when there is a reproduction, is that each member of the pair contributes a haploid gameto, so that from each reproductive cell or gameto of each, the zygote would form, which would again be a diploid cell (46). Chromosomes).
- Polyploids
When the number of chromosomes of a cell or all is an exact multiple of the normal haploid number (23), that cell is said to be euploid, ie it has 46 chromosomes.
Nowadays, thanks to different techniques of cell staining, we can count the number of exact chromosomes that exist, and if for any reason the number of chromosomes of a cell or all cells is an exact multiple of the number Haploid And other than the number Diploid Normal, we talk about polyploidy.
If the number of copies of each chromosome is three, it would be called triploidia, if it is four, tetraploidia, etc.
One of the causes of triploidia may be that an egg has been fertilized by two spermatozoa. Obviously it is not viable in the human being, since most end in abortions.
- Aneuploidies
Aneuploidies often occur because in the process of Meiotic division , A pair of chromosomes does not separate, so the gamete or haploid sex cells will have one more chromosome and therefore would be repeated.
- Monosomics
A monosomy occurs when the gamete does not receive the corresponding chromosome, ie, it does not have its homologue. This therefore results in the total number of chromosomes being 45 instead of 46
The only case of viable monosomy is Turner's Syndrome. One woman suffers from every 3,000 born, which is to prove that the X chromosome is essential for normal growth.
- Trisomies
The most frequent type of aneuploidy in the human species is called trisomy. Of all, the sex chromosomes and the chromosome 21, are the most compatible with life.
There are three trisomies of the sex chromosomes that are accompanied by Phenotypes Practically normal: 47XXX, 47XXY or (Klinefelter syndrome) and 47XYY. The first phenotype is female and the other two would be male.
Other alterations that occur in the sex chromosomes are: 48XXXX, Y 48XXYY, etc.
One of the most well known trisomies is Down Syndrome in par.
The others are not viable for the human being, since the children who are born alive, usually die to the few years of life, as it is in the case of the trisomy of the chromosome 13 or Patau Syndrome and the one of the 18.
On the other hand, also diverse syndromes can appear caused by an alteration in the structure of the chromosomes.
Structural alterations of chromosomes
In some cases, the chromosomes lose or gain genetic material (DNA), which implies a structural modification of the chromosome.
We can talk about Deletion When a piece of the chromosome is lost and disappears from the karyotype (eg, cat meow syndrome).
But if that piece is not lost, but joins another chromosome, we would be before a translocation.
To the extent that there is no loss or gain of genetic material, translocations are considered as balanced genetic rearrangements. The most important are reciprocal and robertsonian.
- A Reciprocal translocation : Is nothing more than an exchange of genetic material.
- The Robertsonian translocation : It consists in the union by the centromere of the long arms of two acrocentric chromosomes with loss of the short arms, thus when the two chromosomes merge, in the karyotype appears as only one.
An important fact is that it has been proven that Down syndrome does not present trisomy 21, but in terms of chromosomes are normal, since these have 46. It seems to be that this occurs because of this type of Robertsonian translocation 14-21.
On the other hand, we call inversion if that piece of chromosome stays where it was but oriented in the opposite direction.
If the area that is inverted contains the centromere, the inversion is said to be pericentric. If the investment lies outside the centromere, the investment is said to be paracentric.
Finally we would have the duplication, which happens when a piece of DNA from a chromosome, is copied or duplicated twice.
As you can verify the chromosomal syndromes can be due to both hereditary factors (chromosomal abnormality that is transmitted by a parent even though it is not affected) and by unknown causes, since when they occur at random can not identify which are The risk factors, in order to prevent them.
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