|Year : 1987 | Volume
| Issue : 3 | Page : 143-5
Paternal translocation (1;7) associated with reproductive failure (a case report).
AM Joseph, IM Thomas
A M Joseph
|How to cite this article:|
Joseph A M, Thomas I M. Paternal translocation (1;7) associated with reproductive failure (a case report). J Postgrad Med 1987;33:143-5
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Joseph A M, Thomas I M. Paternal translocation (1;7) associated with reproductive failure (a case report). J Postgrad Med [serial online] 1987 [cited 2021 Jan 21 ];33:143-5
Available from: https://www.jpgmonline.com/text.asp?1987/33/3/143/5272
Balanced translocations between chromosomes 1 and 7 have been earlier reported in three instances.,, Two of these reports, have been associated with reproductive failure, and third5 with the production of unbalanced offspring. This paper reports a case of t (l; 7) (q25; q11) in an Indian family with fertility failure.
A couple was referred for chromosomal analysis having had three first trimester abortions in their four-year-old marriage. A follow-up on this couple had the wife having a fourth abortion and the fifth and sixth pregnancies resulting in phenotypically normal female infants.
The husband was a healthy, 37 year old, phenotypically normal male. He weighed 78 kg, was 179 cm tall and on repeated semen analysis showed a normal sperm count. His only sister was married and had two phenotypically normal children. His mother had had a medical termination of pregnancy. There had been no history of repeated spontaneous abortions in the family except for the husband's maternal grandmother who had had one abortion.
Chromosomal analyses were done on preparations made from peripheral blood by use of standard methodologies. GTG banding was done and 25 metaphases each were analysed from the couple, the husband's parents and his maternal grandmother.
A balanced reciprocal translocation between chromosomes 1 and 7 was observed in both the husband and his mother, the break points being: t(l;7) (1 pter. 1q25
7q11 7qter; 7 pter 7 q 11
1 q25 l qter). [Fig.1]. The wife, the husband's father and his maternal grandmother all had normal karyotypes. His maternal grandfather was dead. The rest of the family was not available for karyotyping.
Apart from reports in hematological disorders and in malignancy, balanced reciprocal translocation between chromosomes 1 and 7 has been associated with either spontaneous abortions, or has been detected through a partially monosomic or trisomic infant.
Partially autosomal monosomies and trisomies, although associated with congenital malformation to varying degrees, are known to be compatible with life. Partial trisomy 1q causes severe malformation and individuals with 1q1 1qter trisomies are reported to have a limited life span., In the literature surveyed, partial monosomy 1q25 1qter has not been reported. Monosomy for such a large segment of 1q is probably lethal. A review of the literature on 7q trisomies and on 7q deletions reports no cases of either monosomy or trisomy of the region 7q11 7qter, possibly due to the nonavailability of such foetuses.
It is interesting to consider the segregation of the quadrivalent at meiosis with reference to the present translocation. Theoretically, the expectation of balanced to unbalanced gametes is 1 : 2 due to the three modes of possible disjunction. A recent study, however, of human translocations in 151 families has shown that a given translocation produced imbalances nearly always by the same mechanism and that the mode of segregation of a particular translocation could be predicted by pachytene diagram drawing. Using such a model it would appear that the 1;7 translocation being reported in this paper is likely to segregate by adjacent 1 disjunction [Fig. 2] the sum of the two centric segment lengths is greater than the two translocation segment lengths, S CS > S TS; shortest CS = longest TS). As a consequence, the gametes formed would always be unbalanced, unless a single crossover was to occur in the region between the centromere and the break point in either one of the two homologously paired regions of the quadrivalent. The predisposition of this particular translocation to adjacent 1 segregation would conspicuously alter the expected theoretical ratios of balanced to unbalanced gametes, balanced gamates being formed only in the event of a specific crossover occuring.
The production of nonviable pregnancies in the present instance is possibly a consequence of both the segregation mode as well as the large amounts of chromosomal material involved in the translocation, which would not, in either monosomic or trisomic proportions, be compatible with life. It is also interesting that 1;7 translocations though associated with reduced male and female fertility, does not appear to have a male-sterilising effect.
Financial assistance from the Department of Science and Technology, Government of India, is gratefully acknowledged. Mr. R, Victor is thanked for his help.
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