Tuesday, 6 May 2008
Genetic link for frequent miscarriage
May 6, 2008
By Syed Akbar
Hyderabad: Certain couples report frequent miscarriages without any valid external reasons. Scientists have now found that such couples undergo miscarriages because of genetic abnormalities, known in scientific jargon as “abnormal karyotype”.
Genetic counselling will help couples with complaint of frequent miscarriage rectify the defect. It will provide them with the options for future pregnancies.A study conducted by senior scientists SB Nair, G Mukundan, BM Paul and others has found that the single most common reason for pregnancy loss is the presence of a chromosome abnormality in the foetus, particularly if the loss occurs early in the pregnancy.
“About 60 per cent of recurrent miscarriages might be caused by chromosomal aberrations in the embryo,” they said. Of the chromosomal abnormalities observed in couples with two or more pregnancy losses, two-thirds were balanced autosomal translocations with the incidence of such translocations in this group being 30 times higher than in the general population.
As part of the research project, the scientists selected 467 couples with history of recurrent miscarriage. Investigations were carried out to rule out nongenetic factors such as placental abruption as the causative factor for multiple abortion. “After that they were enrolled for genetic work-up. Both partners of each couple were karyotyped and out of that we found 30 cases with translocations”.
One of the cases studied was that of a 34-year-old phenotypically normal female. She had three missed abortions. Her partner was found to be phenotypically and clinically normal. All the other clinical parameters of both the partners were within the normal range. Presently they have a chromosomally normal male and a female child. No relevant family history and consanguinity were observed.
In another case, the team studied a 22-year-old phenotypically normalfemale with three missed abortions. Her mother also had a history of five missed abortions - four in the first trimester and one in the second trimester. Her partner was a 31-year-old phenotypically normal male. His sperm count was normal. All the other clinical parameters of both the partners were within the normal range. No consanguinity was seen.
They pointed out that up to 60 per cent of sporadic miscarriages and between 29-60 per cent of recurrent miscarriages might be caused by chromosomal aberrations in the embryo.
“Carriers of balanced translocations are subjected to an increased risk of abnormal chromosomal segregation during meiosis. The consequences include infertility, multiple pregnancy losses and live born abnormal offspring with multiple congenital malformations as a result of chromosomal imbalance,” the scientists observed.
One major genetic reason for recurrent miscarriage is found to be a balanced translocation in either of the parents. Any discrepancy between miscarriage and congenital anomalies caused by unbalanced gametes might depend on the chromosome number and the positions of breakpoints. The risk of having a handicapped child with an unbalanced karyotype depends on the type of translocation and on the sex of the transmitting parent.
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