Medical Genetics - V. M. Zaporozhan 2005

Chromosomal Diseases
Diagnosis of Chromosomal Diseases

Cytogenetic Methods are used to confirm (or establish) the Diagnosis of Chromosomal Disorders. These include:

1. Karyotyping.

2. Sex Chromatin test.

3. Molecular Cytogenetic Methods.

Karyotyping is the primary method in

the diagnosis of all chromosomal disorders, allowing for the comprehensive Analysis of the entire karyotype.

To diagnose syndromes associated with Changes in the number and Structure of Sex Chromosomes, the sex chromatin test (Barr body analysis) can also be used. The number of X chromosomes is determined by the formula:

Class="center">Х = N + 1,

where X is the number of X chromosomes, and N is the number of Barr bodies.

Thus, the number of X chromosomes is always one greater than the number of Barr bodies. The Y-chromatin test can be used to diagnose Y-polysomy syndrome.

Microdeletions and microduplications are generally undetectable by standard karyotyping, even with differential chromosome banding. In such cases, molecular cytogenetic methods (such as FISH) are employed.

Indications for Cytogenetic testing include:

1. Children with a phenotype characteristic of a specific chromosomal disorder.

2. Children with multiple Congenital Malformations or dysmorphic features of undetermined clinical Etiology.

3. Significant psychomotor and physical developmental delay in a child.

4. Children presenting with clinical signs of Hermaphroditism.

5. A history of recurrent (more than 2) spontaneous abortions, stillbirths, or the birth of children with congenital anomalies.

6. Infertile couples.

7. Leukemia (for Differential diagnosis, Treatment efficacy evaluation, and prognosis).

8. Assessment of mutagenic exposures (radiation, chemical).