Translucenza nucaleTutte test combinato del primo trimestre tecniche di diagnostica prenatale si eseguono durante la gravidanza e possono essere invasive o meno. Prevedono l'analisi del cariotipo di cellule fetali ottenute mediante diversi tipi di prelievi invasivi. Il liquido amniotico viene prelevato mediante amniocentesi. Le cellule fetali sospese nel liquido prelevato permettono di ricostruire la mappa cromosomica o cariotipo del feto. Un'altra tecnica prevede un prelievo di cellule fetali dai villi corialimediante la villocentesi.
Prenataltest - test di screening prenatale non invasivo su DNA fetale libero
Tutte le tecniche di diagnostica prenatale si eseguono durante la gravidanza e possono essere invasive o meno. Prevedono l'analisi del cariotipo di cellule fetali ottenute mediante diversi tipi di prelievi invasivi. Il liquido amniotico viene prelevato mediante amniocentesi. Le cellule fetali sospese nel liquido prelevato permettono di ricostruire la mappa cromosomica o cariotipo del feto.
Un'altra tecnica prevede un prelievo di cellule fetali dai villi coriali , mediante la villocentesi. Queste sono due tecniche di tipo invasivo il liquido si preleva tramite puntura in ambedue i casi , ma esistono anche tecniche non invasive. Il NIPT si basa sul conteggio di frammenti dei cromosomi di interesse il 21 nel caso della sindrome di Down presenti nel sangue materno.
Attualmente in Italia sono presenti 3 tipi di test non invasivi prenatali di recente generazione. In base al secondo, invece, si distinguono i test che eseguono il conteggio counting di tutte le sequenze prodotte e quelli che invece eseguono un conteggio di determinati polimorfismi a singolo nucleotide SNPs. Esistono poi test in fase di sperimentazione presso numerosi laboratori. In particolare l'ospedale di Pavia, l'ospedale sant'Anna di Torino, mediante un nuovo test su immunofluorescenza proposto dalla Vanadis e distribuito dalla Perkin Elmer, e altri centri privati.
Infine certe gravidanze hanno condizioni particolari per cui alcuni test non possono essere presi in considerazione, per esempio le gravidanze gemellari, o i casi in cui la gravidanza sia in seguito ad una ovodonazione. III , sentenza 11 maggio , n. Sentenza 10 gennaio - 2 ottobre , n. I test utilizzati debbono quindi rispondere ai requisiti prescritti.
Esattamente dove questa direttiva recita: Il fabbricante o il suo mandatario Organismo Certificato redige, per i dispositivi destinati alla valutazione delle prestazioni, una dichiarazione contenente le informazioni di cui al punto 2 e si accerta che siano soddisfatte le disposizioni pertinenti della presente direttiva.
Le direttive europee sono valide per tutti i test diagnostici in vitro e, ovviamente, non fanno alcun cenno specifico ai test di screening di Diagnosi Prenatale, pertanto, le declaration of conformity non debbono ricoprire tutto il work-flow, ma solo parti specifiche di questo, come ad esempio la preparazione delle "librerie", oppure il software utilizzato cfr. Cionondimeno alcuni laboratori, anche se non richiesto, stanno oramai commissionando, all' Organismo Notificato prescelto, la certificazione di tutto il work-flow producendo, nel documento finale, le varie certificazioni dei successivi step analitici.
Cariotipo — A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. The term is used for the complete set of chromosomes in a species or in an individual organism. Karyotypes describe the chromosome count of an organism and what these chromosomes look like under a light microscope, attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics.
The preparation and study of karyotypes is part of cytogenetics, the study of whole sets of chromosomes is sometimes known as karyology. The chromosomes are depicted in a format known as a karyogram or idiogram, in pairs, ordered by size. The basic number of chromosomes in the cells of an individual or a species is called the somatic number and is designated 2n.
In the germ-line the chromosome number is n. There may, or may not, be sex chromosomes, polyploid cells have multiple copies of chromosomes and haploid cells have single copies. The study of karyotypes is important for cell biology and genetics, Karyotypes can be used for many purposes, such as to study chromosomal aberrations, cellular function, taxonomic relationships, and to gather information about past evolutionary events.
The next stage took place after the development of genetics in the early 20th century, lev Delaunay seems to have been the first person to define the karyotype as the phenotypic appearance of the somatic chromosomes, in contrast to their genic contents. The subsequent history of the concept can be followed in the works of C. Darlington, investigation into the human karyotype took many years to settle the most basic question, how many chromosomes does a normal diploid human cell contain.
Painter in was not certain whether the diploid of humans was 46 or 48, at first favouring 46, but revised his opinion from 46 to 48, considering the techniques of the time, these results were remarkable. In textbooks, the number of human chromosomes remained at 48 for over thirty years, New techniques were needed to correct this error. The work took place in , and was published in , the karyotype of humans includes only 46 chromosomes.
Rather interestingly, the apes have 48 chromosomes. Cromosoma — A chromosome is a DNA molecule with part or all of the genetic material of an organism. Prokaryotes usually have one single circular chromosome, whereas most eukaryotes are diploid, chromosomes in eukaryotes are composed of chromatin fiber.
Chromatin fiber is made of nucleosomes, a nucleosome is a histone octamer with part of a longer DNA strand attached to and wrapped around it.
Chromatin fiber, together with associated proteins is known as chromatin, chromatin is present in most cells, with a few exceptions, for example, red blood cells. Occurring only in the nucleus of cells, chromatin contains the vast majority of DNA, except for a small amount inherited maternally. Chromosomes are normally visible under a microscope only when the cell is undergoing the metaphase of cell division. Before this happens every chromosome is copied once, and the copy is joined to the original by a centromere resulting in an X-shaped structure, the original chromosome and the copy are now called sister chromatids.
During metaphase, when a chromosome is in its most condensed state, in this highly condensed form chromosomes are easiest to distinguish and study. In prokaryotic cells, chromatin occurs free-floating in cytoplasm, as these cells lack organelles, the main information-carrying macromolecule is a single piece of coiled double-helix DNA, containing many genes, regulatory elements and other noncoding DNA.
The DNA-bound macromolecules are proteins that serve to package the DNA, chromosomes vary widely between different organisms. Some species such as certain bacteria also contain plasmids or other extrachromosomal DNA and these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a significant role in genetic diversity.
In prokaryotes and viruses, the DNA is often densely packed and organized, in the case of archaea, by homologs to eukaryotic histones, small circular genomes called plasmids are often found in bacteria and also in mitochondria and chloroplasts, reflecting their bacterial origins. Some use the term chromosome in a sense, to refer to the individualized portions of chromatin in cells. However, others use the concept in a sense, to refer to the individualized portions of chromatin during cell division.
The term was coined by von Waldeyer-Hartz, referring to the term chromatin, in a series of experiments beginning in the mids, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes and it is the second of these principles that was so original.
Amnios — The amniotic sac, commonly called the bag of waters, sometimes the membranes, is the sac in which the fetus develops in amniotes. It is a thin but tough transparent pair of membranes that hold a developing embryo until shortly before birth, the inner of these fetal membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the fetus. The outer membrane, the chorion, contains the amnion and is part of the placenta, on the outer side, the amniotic sac is connected to the yolk sac, the allantois and, via the umbilical cord, to the placenta.
Amniocentesis is a procedure where fluid from the sac is sampled to be used in prenatal diagnosis of chromosomal abnormalities. The amniotic cavity is the closed sac between the embryo and the amnion, containing the amniotic fluid. The amniotic cavity is formed by the fusion of the parts of the fold, which first makes its appearance at the cephalic extremity.
As the amniotic fold rises and fuses over the dorsal aspect of the embryo, at the beginning of the second week, a cavity appears within the inner cell mass and when it enlarges it becomes the amniotic cavity.
The floor of the cavity is formed by the epiblast. Epiblast migrates between the disc and trophoblast. In this way the epiblastic cells migrate between the embryoblast and trophoblast, the floor is formed by the epiblast which later on transforms to ectoderm while the remaining cells which are present between the embryoblast and trophoblast are called amnioblasts.
These cells are derived from epiblast which is transformed into ectoderm. The amniotic cavity is surrounded by a membrane, called the amnion, as the implantation of the blastocyst progresses, a small space appears in the embryoblast, which is the primordium of the amniotic cavity.
Soon amniogenic amnioblasts separate from the epiblast and line the amnion, the epiblast forms the floor of the amniotic cavity and is continuous peripherally with the amnion. The hypoblast forms the roof of the cavity and is continuous with the thin exocoelomic membrane. This membrane along with hypoblast forms the yolk sac. The embryonic disc now lies between the cavity and the primary yolk sac. Cells from the yolk sac endoderm form a layer of tissue, the extraembryonic mesoderm.
If, after birth, the amniotic sac or big parts of the membrane remain coating the newborn. Cellula — The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology.
Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins. Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells. Most plant and animal cells are only under a microscope.
The cell was discovered by Robert Hooke in , who named the unit for its resemblance to cells inhabited by Christian monks in a monastery. Cells emerged on Earth at least 3. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining.
They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0.
Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces.
It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease.
Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes. Translucenza nucale — Since chromosomal abnormalities can result in impaired cardiovasular development, a nuchal translucency scan is used as a screening, rather than diagnostic, tool for conditions such as Down syndrome. However, increased nuchal translucency measurements are associated with non-chromosomal abnormalities such as genetic conditions.
All women, whatever their age, have a risk of delivering a baby with a physical or cognitive disability. The nuchal scan helps physicians estimate the risk of the fetus having Down syndrome or other abnormalities more accurately than by maternal age alone, overall, the most common chromosomal disorder is Down syndrome. The risk rises with age from 1 in pregnancies below age 25, to 1 in at age Most women, especially those with a low risk of having a child with Down syndrome, may wish to avoid the risk to the fetus, in , Sequenom announced the launch of MaterniT21, a non-invasive blood test with a high level of accuracy in detecting Down syndrome.
As of , there are five versions of this screen available in the United States. Blood testing is used to look for abnormal levels of alphafetoprotein or hormones.
The results of all three factors may indicate a higher risk, if this is the case, the woman may be advised to have a more reliable screen such as cell-free fetal DNA screening or an invasive diagnostic test. Screening for Down syndrome by a combination of age and thickness of nuchal translucency in the fetus at 11—14 weeks of gestation was introduced in the s. Nuchal scan is performed between 11 and 14 weeks of gestation, because the accuracy is best in this period, the scan is obtained with the fetus in sagittal section and a neutral position of the fetal head.