Genetics, Cytogenetic Testing And Conventional Karyotype

Excerpt

Cytogenetic testing is the examination of chromosomes to determine chromosome abnormalities such as aneuploidy and structural abnormalities. A normal human cell contains 23 pairs of chromosomes, including 22 pairs of autosomes and a pair of sex chromosomes (XX or XY). Aneuploidy involves having one or more extra chromosomes (e.g., 47 XX +21, 48 XXXY) or having missing chromosomes (e.g., 45 XO). The most common aneuploidies are Down syndrome (trisomy 21), Edward's syndrome (trisomy 18), Turner syndrome (monosomy X), etc.

The types of structural abnormalities are :

1. Duplication: Part of a chromosome is repeated

2. Deletion: Part of a chromosome is missing

3. Translocation: Material between two different chromosomes is exchanged (this exchange may be balanced or unbalanced)

4. Inversion: Part of the chromosome is inverted within the chromosome

5. Insertion: Addition of material from another chromosome.

Cytogenetic testing can be performed in a variety of situations, including solid organ malignancies, hematologic malignancies, congenital diseases. It can be performed prenatally after biochemical screening or ultrasound with abnormal findings. It is also used for parents with multiple miscarriages or significant findings in their pedigree analysis. Postnatally, cytogenetic testing plays a role in distinguishing patients with mosaicism, intellectual disability, autism, or developmental delays.

Cytogenetic analysis can also be utilized to diagnose malignancies, determine appropriate therapy for prognostic stratification. This review explains the types of chromosome analysis, such as karyotyping, fluorescence in situ hybridization (FISH), and chromosomal microarray analysis (CMA).