Chromosomal abnormalities fit into several categories, but on the whole they can be considered as numerical or structural abnormalities.
Chromosomal abnormalities cause various diseases. Abnormalities that affect the autosomes (the 22 paired chromosomes that are similar in men and women) are more common than those involving the sex chromosomes (X and Y). Chromosomal abnormalities fit into several categories, but on the whole they can be considered as numerical or structural abnormalities. Numerical abnormalities include trisomy (an extra chromosome) monosomy (a missing chromosome) to structural abnormalities including translocations (anomalies in which a whole chromosome or parts of chromosomes is erroneously connected to other chromosomes) deletions and duplications of different chromosomes or portions of chromosomes terminology Some specific criteria in the field of genetics are important for the description of chromosomal abnormalities: aneuploidy: the most common chromosomal abnormality caused by an extra or missing chromosome. Karyotype: The full set of chromosomes in the cells of a human. Genotype: The genetic constitution, which is determined by the karyotype. Phenotype: the clinical findings of a person, including the external appearance – the biochemical, physiological and physical factors as determined by genotype and environmental factors (Introduction to Genetics). Mosaic: The presence of ? 2 cell lines that differ in the genotype, although the man is descended from a single fertilized egg. Diagnosis chromosome analysis banding karyotype analysis Chromosomal microarray analysis are usually used for chromosome analysis lymphocytes, except for prenatal examination if amniocytes or chorionic villus cells from the use (s. Amniocentesis). A karyotype analysis involves a blocking of cells in mitosis during metaphase and the staining of the condensed chromosomes. The chromosomes of the individual cells are photographed and their pictures arranged so that they form a karyotype. Various techniques are used to determine the chromosomes in more detail: In the classical belt technology (e.g., G [Giemsa] -, Q [fluorescent] – and C-bands.) Is used a dye to color bands on the chromosomes. The high-resolution chromosome analysis using special culture methods to obtain a high percentage of prophase and prometaphase spreads. The chromosomes are less condensed than in the routine metaphase, and the number of identifiable bands is expanded, whereby a more sensitive karyotype analysis is achieved. The spectral karyotype analysis (also known as chromosome painting) using chromosome-specific different colored fluorescence in situ hybridization (FISH) techniques, which enhance the visibility of certain defects including translocations and inversions. The chromosomal microarray analysis (CMA, also known as comparative genomic hybridization) is a single-step technique, the entire genome on chromosome dose abnormalities, including the propagation (duplication) or decreases (deletions), which may indicate an unbalanced translocation , The single nucleotide polymorphism (SNP) microarray analysis has to make out the additional ability regions with homozygosity, which can be seen in cases where the parents share the same genetic material (blood relatives). and when a uniparental disomy is present (UPD, z. B. both parts of a pair of chromosomes are inherited from a parent). It is important to note that a CMA not balanced rearrangements recognizes (eg. As translocations, inversions) that are not associated with deletions and duplications. Prevention Recently, non-invasive prenatal screening methods have been developed (NIPS) in which cell-free fetal DNA sequences obtained from a maternal blood sample, a pränatels screening for trisomy 21 (Down syndrome), trisomy 13, and trisomy 18 and sex chromosome -Aneuploidie were used. Although NIPS has a good sensitivity and specificity for some chromosomal abnormalities, it is recommended to confirm the results with diagnostic tests. More recently NIPS was as a screening test for general Mikrodeletionssyndrome (eg deletion 22q11.) Used; However, sensitivity and specificity are still relatively low.