Amyoplasia in monochorionic monozygotic pregnancy following interstitial laser.

Amyoplasia is a specific form of arthrogryposis, without any genetic cause. Six to ten percent of amyoplasia cases are one of the monozygotic twins, with the other twin being normal. Failure of maturation of anterior horn cells (AHCs) due to ischemic injury has been postulated as the primary pathological change, leading to arrest in the development of muscle fibers supplied by the affected AHCs with the typical limb positioning seen in amyoplasia. Twin-to-twin transfusion syndrome (TTTS) is an important risk factor for ischemic injury in monozygotic twin pregnancies. We present a case of monochorionic diamniotic twin pregnancy with features of TTTS at 12 weeks who underwent interstitial laser followed by the development of lower limb akinesia in the surviving fetus. Possible causes of amyoplasia are discussed.

The mystery of monozygotic twinning II: What can monozygotic twinning tell us about Amyoplasia from a review of the various mechanisms and types of monozygotic twinning?

Monozygotic (MZ) twins ("identical twins") are essentially unique to human beings. Why and how they arise is not known. This article reviews the possible different types of MZ twinning recognized in the previous article on twins and arthrogryposis. There appear to be at least three subgroups of MZ twinning: spontaneous, familial, and those related to artificial reproductive technologies. Each is likely to have different etiologies and different secondary findings. Spontaneous MZ twinning may relate to "overripe ova." Amyoplasia, a specific nongenetic form of arthrogryposis, appears to occur in spontaneous MZ twinning and may be related to twin-twin transfusion.

Monozygotic twins discordant for homologous Robertsonian translocation trisomy 21 of 46, XX, + 21, der (21;21) (q10; q10) in a twin-to-twin transfusion syndrome, case report.

BACKGROUND: Monozygotic twins are nearly identical in genotype and phenotype because monozygotic twins arise from one fertilized oocyte. In all cases of discordant karyotype in monozygotic twins, trisomy 21 accounts for about one in 385,000. Monozygotic twins discordant for Robertsonian translocation trisomy 21 of the der (21;21)(q10;q10), in which the additional chromosome originates from the father is rare. CASE PRESENTATION: A 28-year-old parous woman, G3P1A0, came to our institution for a dating scan at 8 weeks of gestation. The transvaginal ultrasound examination demonstrated a monochorionic diamniotic pregnancy. She and her husband were healthy, with no family history of trisomy 21 or other congenital diseases. The ultrasound examination of nuchal translucency thickness was discordant in twins at 13 weeks (twin A, NT 1.4 mm with CRL being 65 mm; twin B, NT 7.8 mm with CRL being 69 mm). At 17+ 4 weeks, twin A was normal, but ventricular septal defect and the hypoplastic left heart was detected in twin B. The deepest vertical pocket was 18 mm in twin A (oligohydramnios) and 102 mm in Twin B (polyhydramnios). The bladder in twin A was absent. Ultrasound findings indicated TTTS Stage II. Amniocentesis was performed for the two fetuses. The karyotyping results revealed 46, XX in twin A but 46,XX,+ 21,der (21;21)(q10;q10) in twin B. For twin B, the parents opted for selective fetal termination by radiofrequency ablation. The procedure was uneventful. At 40+ 5 weeks, twin A was born with a birth weight of 4120 g by vaginal delivery. CONCLUSIONS: The early detection of discordant karyotype and twin-to-twin transfusion syndrome is beneficial to the early intervention. In monozygotic twins with a discordant anomaly, the discordant karyotype should be considered.

Chimerism involving a RB1 pathogenic variant in monochorionic dizygotic twins with twin-twin transfusion syndrome.

We report the first case of blood chimerism involving a pathogenic RB1 variant in naturally conceived monochorionic-dizygotic twins (MC/DZ) with the twin-twin-transfusion syndrome (TTTS), presumably caused by the exchange of stem-cells. Twin A developed bilateral retinoblastoma at 7 months of age. Initial genetic testing identified a de novo RB1 pathogenic variant, with a 20% allelic ratio in both twins' blood. Subsequent genotyping of blood and skin confirmed dizygosity, with the affected twin harboring the RB1 pathogenic variant in skin and blood, and the unaffected twin carrying the variant only in blood.

Effect of Chorionicity on Umbilical Cord Blood Acid-Base Analysis of the Second Twin.

Our objective was to determine whether chorionicity affects umbilical cord blood acid-base parameters of the second twin. This was a retrospective cohort of twin pregnancies delivered at ≥23 weeks of gestation at a tertiary hospital from 2010 to 2016. Patients were included if arterial and venous umbilical cord gas results were available for both newborns and chorionicity was confirmed histologically. Exclusion criteria included intrauterine fetal demise of either twin prior to labor, major fetal anomalies, monoamnionicity, uncertain chronicity and twin-to-twin transfusion syndrome. The primary outcome evaluated was the umbilical artery (UA) pH of the second twin. A total of 593 dichorionic (DC) and 86 monochorionic (MC) twin pregnancies were included. No difference in UA pH was observed between MC and DC twins. Among vaginal deliveries (n = 97), the UA pH of the first twin was higher than the second twin (7.26 vs. 7.24; p = .01). Twin-to-twin delivery interval (TTDI) ≥20 min was associated with a higher UA pH in the first twin compared to the second twin (7.25 vs. 7.16, respectively; p = .006). Multivariable logistic regression was used to predict arterial pH < 7.20 for the second twin; the most predictive factors were arterial pH < 7.20 for the first twin, chronic hypertension and prolonged TTDI. Chorionicity was not associated with any acid-base parameter of umbilical cord blood in either the first or second twin. No differences in neonatal outcomes were observed based on chorionicity or birth order. Populations with a lower cesarean delivery rate may yield different findings.

Generalized Arterial Calcification in a Recipient Twin: Discordant Fetal Hemodynamics Result in Differing Phenotypes in Monozygotic Twins with an ABCC6 Mutation.

Recipients of the twin-twin transfusion syndrome (TTTS) often develop cardiac manifestations, but arterial calcification has rarely been reported. Generalized arterial calcification of infancy (GACI) is a genetic disorder with high infantile mortality. We report the case of a TTTS recipient with moderate cardiomyopathy at diagnosis who developed progressive calcification of the pulmonary arteries and aorta after successful in utero laser therapy. Postnatally, both twins were diagnosed with a heterozygous ABCC6 gene mutation associated with GACI. The recipient had progressive supravalvular pulmonary and aortic stenosis, was treated with bisphosphonate therapy, and successfully underwent cardiac surgery at 4 months of age. The donor twin with the same mutation remained phenotypically normal at 15 months of age. This case illustrates monozygotic fetuses with discordant in utero hemodynamics, with subsequent development of phenotypic differences. TTTS recipients with arterial calcifications should undergo genetic testing for GACI.

Effects of Intrauterine Environment on the Magnitude of Differences Within the Pairs of Monozygotic and Dizygotic Twins.

The aim of this study was to determine the effects of intrauterine environment on the magnitude of intrapair differences in six somatic traits of monozygotic (MZ) and dizygotic (DZ) twins (1,263 pairs; 424 MZ twins and 839 DZ twins). Differences in intrauterine environments of MZ twins enforced division of the research material into four groups: (1) MZ-MC-TTTS - MZ twins from monochorionic (MC) pregnancies with twin-to-twin transfusion syndrome (TTTS), (2) MZ-MC (without TTTS)-MZ twins from MC pregnancies without TTTS, (3) MZ-DC-MZ twins from dichorionic (DC) pregnancies, and (4) DZ-DZ twins. The intrapair differences in all analyzed somatic traits, especially body weight and circumference of the chest, were the largest in the case of MZ twins from MC pregnancies with TTTS. DZ twins were the group presenting with the second largest intrapair differences in the analyzed traits. At the end of pregnancy, that is, in lunar months 9 and 10, the magnitude of intrapair differences in all traits of twins from this group was significantly greater than in MZ twins from both MC and DC pregnancies. Irrespective of the analyzed period, the least evident, statistically insignificant intrapair differences in the studied traits were documented in the case of MZ twins from MC pregnancies without TTTS and twins from DC pregnancies. These findings imply that the differentiating effect of intrauterine environment is associated with the occurrence of TTTS, rather than with chorionicity, as postulated previously.

The Outcome of Monochorionic Diamniotic Twins Discordant at 11 to 13+6 Weeks' Gestation.

BACKGROUND: Monochorionic diamniotic (MCDA) twin pregnancies are associated with adverse perinatal outcome. Intertwin discordances at the time of nuchal translucency (NT) screening may have a value in the prediction of fetal loss or twin-to-twin transfusion syndrome. We aimed to determine the ability of intertwin NT and crown rump length (CRL) discordances among MCDA twins to predict adverse outcomes. MATERIAL AND METHODS: All MCDA twins with a documented routine ultrasound at 11 to 13+6 weeks' gestation, and known pregnancy outcome between August 2003 and August 2012 were included. Receiver operating characteristic curves were used to determine the ideal NT and CRL discordances cut-off points that maximized the ability to predict adverse outcome, which was defined as any of: death of one or both twins, twin-to-twin transfusion syndrome, or estimated fetal weight or birth weight discordances ≥25%. RESULTS: Of the 89 cases, 20 (22.5%) had at least one adverse outcome. NT discordance was more discriminatory of adverse outcome than was CRL discordance. The optimal values for predicting any adverse outcomes for NT were >23.7% and for CRL >3.5%. The positive predictive values for NT (52.4%) and CRL (29.8%) screening were relatively low; however, the lack of either NT or CRL discordances was more reassuring, with negative predictive values of 86.8% and 86.4%, respectively. CONCLUSIONS: NT discordance is more predictive for adverse fetal outcome in MCDA twins than CRL discordance. Neither NT nor CRL discordance are likely to modify the intensive monitoring required for these very high-risk pregnancies.

Comparison Between Monochorionic and Dichorionic Placentas With Special Attention to Vascular Anastomoses and Placental Share.

Placental vascular anastomoses in twins lead to a shared circulation and may subsequently enable the development of severe complications such as twin-twin transfusion syndrome (TTTS) and twin anemia-polycythemia sequence (TAPS). The presence of vascular anastomoses has frequently and systematically been studied in monochorionic (MC) placentas, but only rarely in dichorionic (DC) placentas. The aim of this study was to compare the prevalence of vascular anastomoses and evaluate the sharing discordance in MC and DC placentas. All consecutive placentas of MC and DC twins delivered at the Leiden University Medical Center (the Netherlands) and Medical University of Warsaw (Poland) from 2012 to 2015 were routinely injected with colored dye and included in the study. We excluded twin pregnancies treated with fetoscopic laser surgery. A total of 258 placentas were analyzed in this study, including 134 MC placentas and 124 DC placentas. Vascular anastomoses were present in 99% (133/134) of MC placentas and 0% of DC placentas (p < .01). Placental share discordance between MC twins was significantly larger compared to DC twins, 19.8 (interquartile range [IQR] 8.1-33.3) and 10.8 (IQR 6.2-19.0), respectively (p < .01). Vascular anastomoses associated complications occurred in 16% (22/134) MC twins. Our findings show that vascular anastomoses are almost ubiquitous in MC placentas, but non-existent in DC placentas. In addition, unequal placental sharing appears to be more common in MC than in DC placentas.

The pathway not taken: understanding 'omics data in the perinatal context.

OBJECTIVE: 'Omics analysis of large datasets has an increasingly important role in perinatal research, but understanding gene expression analyses in the fetal context remains a challenge. We compared the interpretation provided by a widely used systems biology resource (ingenuity pathway analysis [IPA]) with that from gene set enrichment analysis (GSEA) with functional annotation curated specifically for the fetus (Developmental FunctionaL Annotation at Tufts [DFLAT]). STUDY DESIGN: Using amniotic fluid supernatant transcriptome datasets previously produced by our group, we analyzed 3 different developmental perturbations: aneuploidy (Trisomy 21 [T21]), hemodynamic (twin-twin transfusion syndrome [TTTS]), and metabolic (maternal obesity) vs sex- and gestational age-matched control subjects. Differentially expressed probe sets were identified with the use of paired t-tests with the Benjamini-Hochberg correction for multiple testing (P < .05). Functional analyses were performed with IPA and GSEA/DFLAT. Outputs were compared for biologic relevance to the fetus. RESULTS: Compared with control subjects, there were 414 significantly dysregulated probe sets in T21 fetuses, 2226 in TTTS recipient twins, and 470 in fetuses of obese women. Each analytic output was unique but complementary. For T21, both IPA and GSEA/DFLAT identified dysregulation of brain, cardiovascular, and integumentary system development. For TTTS, both analytic tools identified dysregulation of cell growth/proliferation, immune and inflammatory signaling, brain, and cardiovascular development. For maternal obesity, both tools identified dysregulation of immune and inflammatory signaling, brain and musculoskeletal development, and cell death. GSEA/DFLAT identified substantially more dysregulated biologic functions in fetuses of obese women (1203 vs 151). For all 3 datasets, GSEA/DFLAT provided more comprehensive information about brain development. IPA consistently provided more detailed annotation about cell death. IPA produced many dysregulated terms that pertained to cancer (14 in T21, 109 in TTTS, 26 in maternal obesity); GSEA/DFLAT did not. CONCLUSION: Interpretation of the fetal amniotic fluid supernatant transcriptome depends on the analytic program, which suggests that >1 resource should be used. Within IPA, physiologic cellular proliferation in the fetus produced many "false positive" annotations that pertained to cancer, which reflects its bias toward adult diseases. This study supports the use of gene annotation resources with a developmental focus, such as DFLAT, for 'omics studies in perinatal medicine.

Predominantly placenta-expressed mRNAs in maternal plasma as predictive markers for twin-twin transfusion syndrome.

OBJECTIVE: This study aimed to identify a set of predominantly placental (PP) mRNAs, which are associated with later-developing twin-to-twin transfusion syndrome (TTTS). METHOD: First, out of 50 PP mRNAs we previously reported, we select target mRNAs that are ordinarily detectable in maternal plasma. Plasma concentrations of these PP mRNAs were measured in monochorionic diamniotic twin (MCDA-T) pregnancies complicated by TTTS later (n = 11) and in uncomplicated MCDA-T pregnancies (n = 17). Finally, the diagnostic values of the PP mRNAs in plasma were evaluated. RESULTS: From 50 PP mRNAs, nine [human placental lactogen (hPL); pregnancy-specific glycoproteins 2 (PSG2); human pregnancy-specific glycoproteins 3 (PSG3); syncytin; syncytin 2; retinoic acid-induced 14; A disintegrin and metalloproteinase domain-containing protein 12 (ADAM12); chorionic glycoprotein hormones, alpha polypeptide; and chorionic glycoprotein hormones, and beta polypeptide] were selected as target mRNAs. Changes in six PP mRNAs [increased hPL, PSG2, and PSG3 and decreased syncytin, syncytin2, and ADAM12] in maternal plasma were detected in MCDA-T pregnant women who subsequently developed TTTS. Finally, mRNA signatures gave elevated AUCs (hPL/PSG2: 0.8717; hPL/PSG3: 0.8449; hPL/ADAM12: 0.8396) compared with single hPL mRNA. CONCLUSION: Quantitative aberration of plural cell-free PP mRNAs in maternal plasma precedes the appearance of clinically apparent TTTS. This suggests that pathophysiological changes in the placenta are associated with morbid conditions of TTTS.

Severe retinopathy of prematurity with retinal detachment in monozygotic twins.

We report a monochorionic diamniotic twin pair born at 29 weeks of gestation in which both twins developed severe retinopathy of prematurity (ROP) with retinal detachment. The pregnancy was terminated due to reversal of donor-recipient phenotypes in possible TTTS. Both twins had unstable cardiopulmonary status during the first week, and developed chronic lung disease. The larger twin, born at 1372 g, developed stage 4a ROP in both eyes, and the smaller twin, born at 1168 g, developed stage 4a ROP in the left eye. Genetic analysis of NDP, FZD4, LRP5, TSPAN12 genes revealed no mutations; however, VEGF gene polymorphism analysis showed heterozygous carrier state of the VEGF 936T allele in both twins, which is a risk factor for threshold ROP in Japanese newborn infants. We speculate the synergistic effects of unstable perinatal cardiopulmonary status and genetic predisposition due to VEGF 936C>T polymorphism caused the development of severe ROP with retinal detachment.

Chimerism in monochorionic dizygotic twins: case study and review.

Chimerism occurs when an organism contains cells derived from more than one distinct zygote. We focus on monochorionic dizygotic twin blood chimerism, and particularly twin-twin transfusion syndrome in such pregnancies. For years, researchers have understood chimerism to be a common phenomenon in cattle. Although, this review will not delve deeply into animal chimerism, an understanding of chimerism in the animal world can provide clues regarding health implications for human chimeras. This report serves two purposes: an update and assessment of the twins we reported previously in 2010 [Assaf et al., 2010] and a review on dizygotic monochorionic chimeric twins. First, our updated assessment of the twins shows no identifiable regression of Müllerian sex derivatives in the female, and normal neurodevelopment was documented in both. Our research has suggested several key points; one that blood chimerism persists from fetal life to at least age two years. Second, chimerism in humans is not as rare as previously thought, although it has been studied only recently. Third, assisted reproductive technologies appear to increase the risk of monochorionic dizygotic twin pregnancies.

Global gene expression analysis of amniotic fluid cell-free RNA from recipient twins with twin-twin transfusion syndrome.

OBJECTIVE: The objective of this study was to understand the biological pathways involved in twin-twin transfusion syndrome (TTTS) by performing global gene expression analysis of amniotic fluid (AF) cell-free RNA. METHODS: A prospective whole transcriptome microarray study analyzing cell-free RNA in AF from TTTS recipient twins and singleton controls was carried out. Significantly differentially regulated genes in TTTS cases (N = 8) versus matched controls (N = 8) were identified and pathways analyses performed. Significant gene expression differences between stage II TTTS recipients (N = 5) and stage III TTTS recipients with abnormal Doppler measurements (N = 5) were also analyzed. RESULTS: Analysis of paired data from TTTS cases and controls revealed differential expression of 801 genes, which were significantly enriched for neurological disease and cardiovascular system pathways. We also identified cardiovascular genes and pathways associated with the presence of critically abnormal Doppler measurements in stage III TTTS recipients. CONCLUSIONS: This study provides the first transcriptome-wide data on the impact of TTTS on fetal development. Our results show that gene expression involving neurological and cardiovascular pathways are altered in recipient fetuses prior to surgical treatment. This has relevance for the origins of long-term complications seen in survivors and for the development of future fetal biomarkers.

Maternal cell-free messenger RNA in twin pregnancies: the effects of chorionicity and severe twin to twin transfusion syndrome (TTTS).

OBJECTIVE: To investigate the effects of chorionicity and severe twin to twin transfusion (TTTS) on maternal circulating cell-free messenger RNA (cf-mRNA). DESIGN: Prospective cohort study. SETTING: A UK tertiary referral Fetal Medicine Center. POPULATION: All monochorionic (MC) twins complicated by severe TTTS (n= 23) and a cohort of uncomplicated dichorionic (DC) (n= 10) and MC (n= 7) pregnancies, between October 2006 and December 2007. METHODS: Maternal cf-mRNA encoding glyceraldehyde 3-phosphate dehydrogenase (GAPDH), vascular endothelial growth factor receptor 1(VEGFR-1(Flt-1)), vascular endothelial growth factor A (VEGF-A), Endoglin, placental growth factor (PlGF), tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (Tie-1), angiopoietin 1 (Ang-1) and angiopoietin 2 (Ang-2) were measured by a quantitative two-step real-time PCR assay after extraction from maternal plasma. RESULTS: The amounts of cf-mRNA detectable are reported for uncomplicated DC, MC and TTTS pregnancies, respectively: GAPDH - 80, 100 and 96%; VEGFR-1 - 10, 0 and 26%; VEGF-A- 80, 71 and 96%; Endoglin-70, 71 and 91%; PlGF-70, 57, 26%; Tie-1 0, 43, 0%; Ang-1 71, 50 and 60% and Ang-2 83, 50 and 89%. There was a significant difference in VEGF-A (medians DC -337.3, MC - 390.8, TTTS - 618.6 copies/mL plasma p= 0.024), Endoglin (medians DC-14.49, MC-1171, TTTS - 2896 copies/mL plasma p= 0.027) and Ang-2 (medians DC-13.66, MC-8.49, TTTS 44.80 copies/mL plasma p= 0.007). CONCLUSION: Maternal cf-mRNA could be reliably detected for GAPDH, PlGF, VEGF-A, Endoglin, Ang-1 and Ang-2 in twin pregnancies and a significant difference was demonstrated in VEGF-A, Endoglin and Ang-2 between uncomplicated twins and MC twin pregnancies complicated by TTTS. If such alterations in maternal cf-mRNA precede the onset of clinically apparent disease, this may be used as an adjuvant blood test to complement ultrasound screening.

Prenatal diagnosis and outcome of multiple pregnancies with reversed arterial perfusion (TRAP-sequence).

OBJECTIVES: We analyse the prenatal detection and pregnancy outcome of twin reversed arterial perfusion syndrome (TRAP-sequence) in monochorionic twin pregnancies. METHODS: We included all cases in which the prenatal diagnosis of a TRAP-sequence had been established and reviewed the prenatal, obstetrical, and pathological records of the acardiac twin as well as the neonatal/pediatric records of the donor twin. Minimal follow-up for the donor twin after birth was 6 months. RESULTS: We detected six cases of TRAP-sequence in 412 examined monochorionic multiple pregnancies (incidence 1.46%) Mean gestational age at diagnosis was 20.4 (13.1-28.0) gestational weeks. All donor twins survived without detectable mid- or long-term sequelae. There was neither missed prenatal diagnosis nor a false-positive diagnosis of TRAP-sequence. Mean birthweight of the acardiac twins was 1,400 g (830-2800 g). There was an uneventful medical history in the maternal records of all included women. Fetal karyotype was available for 5/6 twin-pairs, all revealing a normal distribution of the chromosomes. All acardiac twins had post-mortem examination with specification of the subtypes of acardiac twin displaying 3/6 acardius acephalus, 2/6 acardius amorphus, and 1/6 acardius anceps. CONCLUSIONS: The antenatal diagnosis of TRAP-sequence is feasible and can be established during the first-trimester-screening. The discrimination of the adequate time to end the pregnancy, though a crucial concern, remains a challenging question. Future studies should address this topic.

[Conservative management of deformed twin pregnancy]. / Konservativ behandling af et stort misdannet tvillingeanlæg.

A twin reversed arterial perfusion (TRAP) sequence was diagnosed in a monochoriotic, diamniotic twin pregnancy at GA 12 weeks + 2 days. According to the parents' wish the pregnancy was managed conservatively with close monitoring, with ultrasound biometry and Doppler flow measurements in the umbilical artery, middle cerebral artery and ductus venosus. At GA 34 weeks + 0 days the TRAP twin was growing rapidly and the amnion fluid index was increasing rapidly. An uncomplicated elective section was performed. The acardiac/pump twin weight ratio was 134%. The pump twin was without sequelae.

Association of COMT genotypes with S-COMT promoter methylation in growth-discordant monozygotic twins and healthy adults.

BACKGROUND: Catechol-O-Methyltransferase (COMT) plays a key role in dopamine and estrogen metabolism. Recently, COMT haplotypes rather than the single polymorphism Val158Met have been reported to underlie differences in protein expression by modulating mRNA secondary structure. So far, studies investigating the epigenetic variability of the S-COMT (soluble COMT) promoter region mainly focused on phenotypical aspects, and results have been controversial. METHODS: We assessed S-COMT promoter methylation in saliva and blood derived DNA with regard to early pre- and postnatal growth as well as to genotype for polymorphisms rs6269, rs4633, and rs4680 (Val158Met) in 20 monozygotic twin pairs (mean age 4 years), who were discordant for intrauterine development due to severe feto-fetal-transfusion syndrome. Methylation levels of two previously reported partially methylated cytosines were determined by the quantitative SIRPH (SNuPE- IP RP HPLC) assay. RESULTS: Overall, we observed a high variability of S-COMT promoter methylation, which did not correlate with individual differences in the pre- or postnatal growth pattern. Within the twin pairs however we noted a distinct similarity that could be linked to underlying COMT genotypes. This association was subsequently confirmed in a cohort of 93 unrelated adult controls. Interestingly, 158Val-alleles were found at both ends of the epigenotypical range, which is in accordance with a recently proposed model of COMT haplotypes corresponding to a continuum of phenotypical variability. CONCLUSION: The strong heritable component of S-COMT promoter methylation found in our study needs to be considered in future approaches that focus on interactions between COMT epigenotype and phenotype.

Blood chimerism in a girl with Down syndrome and possible freemartin effect leading to aplasia of the Müllerian derivatives.

Cytogenetic and molecular genetic analysis in a case of sex-discordant dizygotic twins revealed blood chimerism in the girl (46,XY in blood and 47,XX, + 21 in fibroblasts) caused by feto-fetal transfusion from her healthy brother. The girl presented with Down syndrome, aplasia of the uterus and the Fallopian tubes and normal female external genitalia. We propose that the lack of Müllerian structures is caused by the effect of the Müllerian inhibiting substance transferred from the male to the female twin in early pregnancy. This disorder of sex development is known as freemartin phenomenon in female cattle from sex-discordant twin pairs.