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Re: ULTRASOUND digest 1595From: Wolfgang Moroder, MD (womorode@tin.it)Tue May 7 14:35:43 2002
This might be a case which might give you some clues for your question and I 'd like to share it with you. Since I was quite puzzled from a case of monochorionic twins I thought of writing to Prof Bernischke and asked his opinion. I scanned a patient at 8+4 weeks with the following findings: two amniotic sacs, two yalk sacs in a common extracelomic space. I actually used the pictures to demonstrate a monochorionic pregnancy in a couple of talks I gave on early scanning in twin pregnancy: I thought that these findings are proof of a monochorionic that means also monozygotic twin pregnancy. You cannot imagine my surprise when at 20 weeks I found that the twins were incontrovertibly discordant for the gender. What is the biological explanation for that? Is it possible that identical twins are only discordant in the phenotypus? Do dizygotic twins have only one extracelomic space? Answer: Dear Dr. Moroder: This set of twins is VERY unusual, as you correctly interpreted. The fact that they are of different gender is perhaps significant, but not necessarily PROOF that they are dizygotic. There are numerous cases described where a set of monozygotic twins were discordant for sex chromosome, where one baby is 46XY, the other 45XO. During early embryogenesis a Y-chromosome got lost and the other twin develops as a Turner's syndrome. When they are monochorionic, they often then also have blood chimerism, but that does not always happen. That is the first possibility - socalled heterokaryotypic twins (p. 846 in my book:Pathology of Human Placenta, Springer-Verlag, 2000, 4th edition). But it is also true that VERY few dizygotic twins developed in a single chorionic sac and result then in blood chimerism. In fact, a rare case has even developed the transfusion syndrome, but only 4-5 cases are known to me that can be seen to be PROVEN. In fact, the first good case (color picture in the first edition of my book) was from Cameron in England and he subsequently showed that the twins (dichorionic though they were and chimeric) had been identical twins with anastomosis. I recommend that you wait until the twins are born and do karyotypes on them. I would be inclined to anticipate Turner in one. I hope this clarifies the situation. You should know though that in marmoset monkeys this is the REGULKAR mode of placentation and it occurs in cattle and a few other ungulates as well. Mit besten Gruessen, K. Benirschke Kurt Benirschke, M.D. Home: 8457 Prestwick Drive, La Jolla, CA 92037 Tel: 858-459-9132. FAX: 858-459-1063. Office: UCSD Medical Center, 200 West Arbor Drive, San Diego, CA 92103-8321. Tel.: 619-543-2618; Office(Agnes):619-543-5719. Fax: 619-543-7711.e-mail: kbenirsc@ucsd.edu Please visit my Website on Comparative Placentation at: http://medicine.ucsd.edu/CPA
At Tue, 7 May 2002, Regnifob@aol.com wrote:
>
-- Wolfgang Moroder, MD Prenatal Unit Bolzano General Hospital Italy
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