Chromosomal abnormalities are often responsible for infertilities, abortions, and babies born with mild to severe birth defects. Dr Vaasavi Narayanan, head of Cytogenetics department, Apollo Diagnostics, Pune mentioned “there are many rare chromosomal abnormalities in cases referred for infertility or from the pediatrics departments”. Therefore, it is important to have chromosome testing done.
“Down syndrome is commonly diagnosed in the clinic in newborns and confirmed by chromosome testing. In addition, there may be rare numerically abnormal variants like the presence of an XXY syndrome along with trisomy 21, which if evaluated properly, can help in appropriate management of these Down’s children. Another such rare finding is the presence of an extra Y chromosome, giving rise to 47, XYY or Jacob syndrome in a male. This abnormality is reported in 1 in 1,000 male births, and we have seen one case in past four years,” she mentioned.
What are chromosomal abnormalities?
Normally, a fertilised egg should lead to the formation of a foetus with 46 chromosomes that includes two sex chromosomes – XX for female and XY for a male. However, if there is an extra or missing chromosome, it is termed as a numerical abnormality. Apart from this, the chromosome number may remain the same but there may be structural rearrangements in chromosomes leading to loss or gain of segments – both these situations may lead to pregnancy loss or birth of a child with a defect.
Cytogenetic diagnostic tests can screen for and also give the chances for pregnancy loss or the possibility of an abnormal baby in prospective parents. Some of these tests are invasive for definitive prenatal diagnosis (in high-risk individuals) and give the parents the option to decide about continuing the pregnancy or prepare them for a child that may require additional medical attention at birth”, adds Dr Narayanan.
There are other rare structural chromosomal abnormalities like the presence of a ring chromosome. This happens when there is breakage of the end segments of a chromosome and subsequent rejoining of the sticky ends.
“Ring chromosome 12 is a rare finding and shows a highly variable phenotype, depending on the extent of chromosomal material lost or duplicated during the formation of the abnormal ring structure. These individuals may present with symptoms such as growth retardation, intellectual disability, skeletal defects, and even infertility. In some cases of a ring with negligible loss of chromosomal material, the person barely shows any problems other than infertility. In these cases, a chance of successful pregnancy is better with IVF. Patients presenting with infertilities and multiple abortions should be evaluated for cytogenetic studies to rule out chromosomal causes,” she mentioned.
How does chromosomal abnormalities hamper a child’s growth?
Individuals may have learning disabilities, presenting with dyslexia, gain abnormal height which may be obvious by the time they are 6-7 years of age. With respect to rare anomalies related to the Y chromosome, there may be fertility issues in individuals showing chromosome Y inversion, also reported in less than 1 in 1000 male births. Such cases could further be evaluated for Y microdeletion studies before referring for IVF, added Dr Narayanan.
So, how does chromosomal testing of embryos help?
Dr Karishma Dafle, Nova IVF Fertility, Pune explained how chromosomal testing of embryos helps in the detection of abnormalities in patients with recurrent pregnancy loss. “Women should get embryos screened after consulting the doctor if all other causes of pregnancy loss have been ruled out. Pre-Implantation Genetic Testing for Monogenic disorders (PGT-M) is a genetic test of embryos that can be accompanied by an IVF cycle to detect single gene defects and reduce the risk of passing on a specific genetic condition which runs in the family to have a successful pregnancy outcome. PGT-A (Pre-implantation genetic testing for Aneuploidy) refers to testing embryos to look for extra or missing chromosomes so that normal embryo can be selected and transferred to give successful pregnancy. It is carried out on cells that are removed from one’s embryos and the best and unaffected embryos are transferred in mothers womb for preventing genetic diseases”.