Evidence for blood chimerism in dizygotic spontaneous twin pregnancy discordant for Down syndrome.

BACKGROUND: A monochorionic-diamniotic placenta (MCDAP) is rare in dizygotic (DZ) twinning. All reported cases have been documented in pregnancies achieved by the induction of ovulation alone or during the IVF cycle. METHODS AND RESULTS: We report a spontaneous pregnancy in a 39-year-old patient with evidence of MCDAP in DZ twins, discordant for trisomy 21. The first and second-trimester sonographic scans indicated male twins with MCDAP. Amniocentesis, performed because of advanced maternal age, revealed a normal karyotype in one fetus, and trisomy 21 in the other. Molecular studies, performed in order to confirm the zygosity and chorionicity, demonstrated that the fetuses were DZ. In order to identity the affected twin, a detailed sonographic examination was repeated, but no abnormal findings associated with Down syndrome were demonstrated in any of the fetuses. Therefore, umbilical cord blood samples were obtained from both fetuses. Chromosomal analysis revealed in both fetuses two cell lines: a normal cell line of 46,XY and a 47,XY,+ 21 cell line, in 65 and 80% of the cells, respectively. This result was independently confirmed by both FISH and G-banding. DNA extracted from both cord blood samples demonstrated an admixture of two distinct genotypes in each sample. CONCLUSIONS: We propose that this case represents a monochorionic-dizygotic twin pregnancy with blood chimerism. The most plausible mechanism underlying this phenomenon is placental fusion early in pregnancy, resulting in an architecturally single placenta originating from two distinct zygotes. The newly formed blood vessels created anastomoses between the DZ twins and allowed reciprocal blood chimerism between the normal and the trisomic twin.

Diversity of beta-globin mutations in Israeli ethnic groups reflects recent historic events.

We characterized nearly 500 beta-thalassemia genes from the Israeli population representing a variety of ethnic subgroups. We found 28 different mutations in the beta-globin gene, including three mutations (beta S, beta C, and beta O-Arab) causing hemoglobinopathies. Marked genetic heterogeneity was observed in both the Arab (20 mutations) and Jewish (17 mutations) populations. On the other hand, two ethnic isolates--Druze and Samaritans--had a single mutation each. Fifteen of the beta-thalassemia alleles are Mediterranean in type, 5 originated in Kurdistan, 2 are of Indian origin, and 2 sporadic alleles came from Europe. Only one mutant allele--nonsense codon 37--appears to be indigenous to Israel. While human habitation in Israel dates back to early prehistory, the present-day spectrum of beta-globin mutations can be largely explained by migration events that occurred in the past millennium.

[Cordocentesis for prenatal diagnosis].

Cordocentesis for prenatal diagnosis was being performed in the seventies during the process of fetoscopy. Since then the technique has been used as a diagnostic tool for intrauterine infection, hematological and metabolic disorders and metabolic status of the fetus; and for rapid cytogenic analysis. We report our first 207 cordocenteses performed since December 1985. First puncture was successful in half the cases. The procedure resulted in termination of pregnancy in only 0.96% of cases. Though a new technique, cordocentesis is playing a major role in modern perinatology. The possibility of a direct route to fetal blood vessels early in pregnancy would lead to earlier diagnosis and treatment.