cGH-Array based technology

 

What is CGH    (comparative genomic hybridization (CGH)               )? Array based CGH  which is has become a more accurate and objective alternative for the detection of  A) chromosome anomalies  B) balanced rearrangements and C) low‐grade mosaicism . Here comes the role of array based CGH(microarray)  .

What is CGH ? It implies comparative genomic hybridization (CGH) and array based CGH . Array technology has become very relevant in last 3 decades in our discipline too. We know that miscarriage or pregnancy loss (PL) is the spontaneous loss of an embryo or fetus within the first 20 weeks affecting 10%–15% of pregnancies .Most miscarriages occur in the first trimester (under 13 weeks) .Recurrent pregnancy loss is defined as two or more pregnancy losses (Practice Committee of the American Society for Reproductive Medicine, 2012) and affects 3–5 percent of couples .

Pregnancy and fetal loss is caused by many factors, some of which are maternal such as Viral and protozoal (TORCH)  infections, hypothyroidism, diabetes, uterine anatomical abnormalities and etc. Other causes are fetal and some are the result of immune reactions between fetus and mother. The most common fetal cause of  early  pregnancy loss is considered to be chromosomal abnormalities, accounting for half of first trimester and one third of second trimester losses . Traditionally chromosomal analysis of product of conception by karyotyping has been the routine test, which has major limitations including its need for viable tissue, culture failure rates (10%–40%) (maternal cell contamination ); &  more importantly  resolution (usually below 5–10 Mb).

Recently with the advent of new technologies comparative genomic hybridization (CGH) and subsequently array based comparative genomic hybridization (a‐CGH) of DNA extracted from uncultured or paraffin‐embedded product of conception/fetal tissue has become a more accurate and objective alternative for the detection of fetal chromosome anomalies.

 Among the many advantages of this technique is the use of DNA instead of metaphase spreads, which makes study of more samples possible, its objectivity and reproducibility, and its higher resolution .The major limitation of this technique, is its inability to detect polyploidy, low grade mosaicism and balanced rearrangements. Whereas, balanced rearrangements and low‐grade mosaicism are unlikely causes of pregnancy loss, polyploidy accounts for 8%–15% .