pediatrics
Overview of Chromosomal Abnormalities
Diagnosis of Chromosomal Abnormalities
Chromosomal analysis (karyotyping) Banding Fluorescent in situ hybridization (FISH) Chromosomal microarray analysis (array comparative genomic hybridization) (See also Genetic Diagnostic Technologies .) Lymphocytes are typically used for chromosomal analysis, except prenatally, when amniocytes or cells from placental chorionic villi are used (see Amniocentesis and Several techniques are used to better delineate the chromosomes: In classical banding (eg, G [Giemsa]-banding, Q [fluorescent]-banding, and C-banding), a dye is used to stain bands on the chromosomes. High-resolution chromosome analysis uses special culture methods to obtain a high percentage of prophase and prometaphase spreads. The chromosomes are less condensed than in routine metaphase analysis, and the number of identifiable bands is expanded, allowing a more sensitive karyotype analysis. Spectral karyotyping analysis (also called chromosome painting) uses chromosome-specific multicolor fluorescent in situ hybridization (FISH) techniques that improve the visibility of certain defects, including translocations and inversions. Chromosomal microarray analysis (CMA), also called array comparative genomic hybridization (aCGH), is a single-step technique that allows the entire genome to be scanned for chromosome dosage abnormalities, including increases (duplications) or decreases (deletions), which may also be suggestive of an unbalanced translocation. Single nucleotide polymorphism (SNP) microarray analysis has the additional ability to detect regions of homozygosity, which may be seen in cases where parents share common ancestry (consanguinity), and also when there is Uniparental disomy (ie, both copies of a chromosome, or part of a chromosome, are inherited from one parent, instead of 1 copy from the mother and 1 copy from the father). It is important to note that CMA does not detect balanced rearrangements (eg, translocations, inversions), which are not associated with deletions or duplications. Noninvasive prenatal screening (NIPS) methods are used for Noninvasive Prenatal Fetal Screening Tests ( 1.American College of Obstetricians and Gynecologists’ Committee on Practice Bulletins—Obstetrics; Committee on Genetics; Society for Maternal-Fetal Medicine: Screening for fetal chromosomal abnormalities: ACOG Practice Bulletin, Number 226.Obstet Gynecol136(4):e48-e69, 2020. doi: 10.1097/AOG.0000000000004084 