A novel chromosome defect responsible for loss of foetal heart beat and leading to miscarriage was recently detected by scientists at the Hyderabad-based Centre for Cellular and Molecular Biology (CCMB).

The novel chromosome defect showing loss of crucial region on chromosome 22, which is associated with absence of heart beat, was detected by the team led by Dr. Lakshmi Rao Kandukuri, group scientist from CCMB in collaboration with Dr. Padmavathi Buddavarapu from Basant Sahney Hospital in Hyderabad. The results of the work were published in Genetic Syndromes and Gene Therapy.

It was found that the defective bi-satellited chromosome 22 was contributed by the male partner or originated in the oligoasthenospermic (infertile) male partner leading to miscarriage due to errors at the stage of meiotic segregation and division. (Satellites are regions containing essential genes that act as foundation for nucleolar structure. The additional chromosome 22 has two satellite regions.) The normal chromosomal complement comprises 46 chromosomes — 22 pairs of different autosomes and a pair of sex chromosomes. Of this 22 pairs of autosomes, five pairs are acrocentric chromosomes with each chromosome having one satellite region.

But in this particular case, it was found that in addition to the normal complement, there was one bi-satellited additional chromosome 22. Besides, there was also a deletion in 22q region, specifically Di George locus, which is crucial for heart development. Apart from the latest finding, Dr. Lakshmi Rao and her colleagues over the past several years have identified novel chromosome defects and mutations associated with recurrent miscarriages, ovarian failure, male infertility, endometriosis and polycystic ovary syndrome in the Indian population. Their research focusing on disorders relating to human reproductive genetics was carried out in collaboration with medical practitioners.

Emphasising the importance of screening for chromosomal abnormalities in couples facing infertility problem as also frequent pregnancy loss by women, Dr. Lakshmi Rao said that normally 15-20 per cent of all pregnancies result in miscarriages. While a range of causes like infections, advanced maternal and paternal age, auto-immune disorders, uterine anomalies and even environmental toxins have been associated with miscarriages, the most predominant cause has been attributed to chromosomal abnormalities — which account for 70 per cent of the miscarriages.

She said earlier studies conducted by her lab showed that six per cent of male infertility was linked to chromosomal abnormalities, while in the case of ovarian failure it was 14 per cent. Sex chromosomes were involved in the abnormalities most of the time.

Mostly, the abnormalities are caused by chromosomal re-arrangement which eventually leads to the gametes having an imbalanced set of chromosome material.

Dr. Rao said routine chromosome analysis of infertile couples was essential before planning for assisted reproductive technologies (ARTs).