Molecular karyotyping (relative hybridization of the genome)

Molecular karyotyping Is a molecular cytogenetic analysis that allows us to accurately and quickly identify those unbalanced chromosomal abnormalities associated with changes in the number of DNA copies (microdeletions and microduplications) that cannot be detected by classical chromosomal analysis.

This method examines the entire genome at a higher resolution and can explain the phenotype 5-10 times more often than the classical karyotyping method, which gives it an advantage in situations where it is impossible to study cell culture.

The test is based on the comparative genomic hybridization (CGH) method of two types of DNA - patient DNA and control DNA sample. It allows the identification of CNV (copy number options), which are classified into 5 categories:

• Benign variations;
• Variations of unknown value (VOUS) (possibly benign);
• VOUS with uncertain meaning;
• Possible pathogenic VOUS;
• Obviously pathogenic VOUS;

These submicroscopic genome distributions (variants) are widespread throughout the genome and represent an important factor for evolution, phenotypic differentiation, and susceptibility to certain diseases.

Molecular karyotyping is used for both examination and diagnostics.

When should we take the test?

Molecular karyotyping is the first test in postnatal diagnostics.

• Patients with multiple congenital defects / dysmorphic signs that are not part of a known genetic syndrome;
• Infants with multiple congenital defects in which karyotype is not acceptable;
• Children with psychomotor developmental delays;
• Patients with intellectual disabilities;
• Patients with autism spectrum disorders;
• Other cases such as growth retardation, delayed onset of speech, etc.

What are the advantages of molecular karyotyping by comparative genomic hybridization method?

• Increased clinical utility. The detection rate of pathogenic CNV (copy number variants) in children with developmental delays, intellectual disability and multiple congenital defects is 18-20%, in the case of classic karyotyping - 3%.
• On average, the detection resolution is high. It offers a perspective with high resolution over the entire genome (10 times higher than in classical karyotyping).
• One test is the equivalent of thousands of FISH / MLPA experiments;
• Detects submicroscopic duplications, deletions, unbalanced chromosomal rearrangements, and varying degrees of mosaicism.
• Cell culture is not required for the study.

Test diagnostic limitations

• Does not detect balanced chromosomal changes (displacements, inversions, insertions), point mutations, low-level mosaicism. These changes are detected by other genetic tests;
• It does not provide information on the structural nature of the identified anomalies;
• It can detect CNVs of unknown significance that require further testing and analysis.

What is the role of the geneticist?

Research requires a geneticist consultation.

The role of the geneticist is important because genetic counseling before and after testing helps the patient understand the advantages and limitations of the method as well as the test result.

Phenotypic patient data are essential for the interpretation of outcomes, and close collaboration with the physician helps to make accurate diagnoses and improve patient management.

How to prepare for the test?

No special preparation is required for the test.

Research material

Venous blood

Possible interpretation of the results

Molecular karyotyping describes detected, unbalanced quantitative and structural changes (loss or gain of genetic material), breakpoints, exact measurements of changes.

The final clinical interpretation of the result is made by the geneticist, depending on the patient's phenotype and the genetic content of the chromosomal regions involved in the changes.

The test can be confirmed, depending on the situation, by classical cytogenetic or molecular methods such as FISH or qPCR / MLPA.

Resources

https://www.synevo.ro/shop/cariotip-molecular-hibridizarea-genomica-comparativa/