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    Genomics

    Chromosomal Microarray (CMA)

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    Overview 

    Chromosomal microarray (CMA) is a cutting-edge genetic technique that enables highresolution detection of copy number variations (CNVs) across the entire genome. It is a powerful molecular genetic technique used to detect chromosomal abnormalities at a higher resolution compared to traditional cytogenetic methods like karyotyping. It works by hybridizing DNA samples from a patient and a reference onto a microarray slide containing numerous DNA probes. By measuring fluorescence intensity, CMA identifies gains or losses of genetic material, pinpointing anomalies associated with conditions like autism, intellectual disabilities, and congenital disorders.

    Methodology

    1. Sample Preparation

    CMA typically requires a sample of DNA extracted from cells, often obtained from peripheral blood, amniotic fluid, chorionic villus sampling (CVS), or other tissue sources.

    2. Probe Design

    Two main types of probes are used in CMA: oligonucleotide arrays and comparative genomic hybridization (CGH) arrays. These probes are designed to hybridize with DNA sequences across the entire genome or specific regions of interest.

    3. Hybridization

    DNA from the patient (test sample) is labeled with a fluorescent dye and hybridized to the microarray, which contains thousands to millions of probes representing different genomic regions.

    4. Data Acquisition and Analysis

    The array is scanned to detect fluorescence signals, which indicate the relative quantity of DNA in the patient’s sample compared to a reference sample (often a normal control). Software is used to analyze these signals and identify chromosomal gains, losses, or other structural abnormalities.

    Applications

    • Prenatal Diagnosis: Detects genetic abnormalities in fetuses during pregnancy.
    • Postnatal Diagnosis: Identifies genetic causes of developmental delays, intellectual
      disabilities, and congenital anomalies.
    • Cancer Genetics: Assesses genomic alterations in cancer cells, aiding in diagnosis and
      treatment decisions.
    • Reproductive Health: Evaluates causes of infertility, miscarriages, and recurrent pregnancy
      loss.
    • Research: Facilitates genome-wide association studies (GWAS) and investigation of genetic factors in various diseases.

    Criteria for Use

    • Clinical Presentation: Patients with suspected genetic disorders, developmental delays, unexplained intellectual disabilities, or multiple congenital anomalies.
    • Diagnostic Uncertainty: When conventional testing methods (like karyotyping) fail to provide a diagnosis.
    • Family History: Presence of genetic conditions in family members that suggest a hereditary component.
    • Prenatal Testing: In cases of abnormal ultrasound findings or increased risk based on maternal age or other factors.

    Sample Requirements

    • Blood : Peripheral blood is commonly used for postnatal testing. (Quantity needed 2-3 ml)
    • Amniotic Fluid : Obtained through amniocentesis during pregnancy. (Quantity needed 10ml with EDTA Blood for MCC)
    • Chorionic Villus Sampling (CVS) : Tissue obtained from the placenta early in pregnancy.(Sample along with EDTA Blood for MCC)
    • Tissue Biopsy: Samples from affected tissues in cases such as cancer or other specific conditions. (Sample along with EDTA Blood for MCC)

    CMA 315 K

    • Resolution: Medium to high.
    • Probe Coverage: Covers a substantial portion of the genome.
    • Applications: Used for routine clinical diagnostics and basic research.
    • Advantages: Cost-effective, detects common genetic abnormalities effectively.

    CMA 750 K

    • Resolution: Ultra-high.
    • Probe Coverage: Dense array covering a large portion of the genome.
    • Applications: Ideal for complex genetic conditions, cancer genetics, and advanced research.
    • Advantages: Detects very small genetic changes, suitable for rare variants and precise diagnostics.
    CMA 315 K : Offers medium to high resolution, suitable for routine clinical diagnostics and basic research.
    CMA 750 K : Provides ultra-high resolution, designed for detailed analysis of complex genetic conditions, cancer genetics, and advanced research applications

    Choosing between CMA 315 K
    and CMA 750 K depends on the specific needs of the study or diagnostic scenario, including the desired level of resolution, scope of analysis, and budget considerations. For routine clinical use and broader genetic screening, CMA 315 K may be sufficient, whereas CMA 750 K is preferred for applications requiring high sensitivity and comprehensive genomic analysis.

    In summary, chromosomal microarray is a versatile tool in clinical genetics, offering highresolution analysis of chromosomal abnormalities across various applications. Its ability to detect subtle genetic changes has revolutionized genetic diagnosis and management, particularly in prenatal and pediatric settings where early and accurate diagnosis can significantly impact patient care and outcomes.