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Cytogenetics

is the study of chromosomes by a microscope. It is used to study an individual’s chromosomes makeup (karyotype). A normal human karyotype is composed of 22 pairs of autosomal chromosomes and one pair of sex chromosomes: XX in females and XY in males. Cytogenetic testing determines the number of chromosomes, and evaluates each individual chromosome for structural abnormalities such as deletions, translocations and duplications. Specimens for Cytogenetic studies include peripheral blood, bone marrow, amniotic fluid, products of conception, solid tumors and skin biopsies.

Conventional Cytogenetics is aided by newer techniques such as Fluorescence in situ hybridization (FISH) that can improve the accuracy of karyotyping.

Cytogenetic abnormalities can be constitutional or acquired:

  • Constitutional abnormalities: refer to those present at birth. These conditions present clinically with a variety of findings, including congenital anomalies, and abnormalities in Intellect and growth. An example of constitutional abnormalities is Trisomy 21 (Down Syndrome).
  • Acquired abnormalities: refer to those not present at birth but are acquired after birth. Typically these abnormalities are associated with premalignant and malignant conditions.
Many hematologic malignancies such as Leukemia and Lymphoma are associated with clonal chromosomal abnormalities. In addition, these chromosomal abnormalities are found in many solid tumors such as Ewing sarcoma.
 
Cytogenetic studies are able to detect these abnormalities and aid in the diagnosis and treatment of such disorders.
 
 

Fluorescent in situ Hybridization (FISH)

is a relatively new technique using fluorescent labeled DNA probes to detect chromosomal abnormalities that sometimes can be difficult to identify using conventional Cytogenetics karyotyping.

FISH is a powerful tool that offers rapid, sensitive and specific detection of chromosomal abnormalities including deletions and translocations.

 

Many FISH probes are available and are utilized in diagnosing genetic anomalies in a variety of clinical settings including congenital genetic disorders and malignant tumors.

A few widely used FISH probes include HER2/neu in Breast cancer, UroVysion in Bladder cancer, BCR/ABL in Chronic Myelogenous Leukemia (CML), and PML/RARA in Acute Promyelocytic Leukemia (APL).

 

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