We previously studied a pair of MZ twins with situs viscerum inversus of the heart, liver and stomach, concordant with regard to all other factors normally utilized to diagnose zygosity [3]. We have now reexamined them after three years to evaluate the development of their cardiovascular system.

Our male MZ twins, now 17 years old, have been examined with high-resolution electrocardiography (HRE), treadmill stress test with Bruce protocol, tests stressing the cardiovascular system (cold pressure test, handgript test, arithmetic mental test), and single and two-dimensional dynamic echocardiography after holter monitoring.

Atriogram analysis is made possible by HRE, that shows individual morphological reproducibility. Such reproducibility is present in both twins. In the dextrocardiac twin it is also present with the electrode position inverted. The similarity of morphology in the cotwins is further confirmed, even if such similarity is only apparent, in view of the fact that the vectors are spatially of opposite orientation, thereby causing an inversion of the electrical field [1-4]. The H-V interval is normal, although in the dextrocardiac twin it is longer (30 ms) than in his cotwin (25 ms). As regards the echocardiographic and dynamic ECG examination, normal data were obtained for both twins which were pratically superposable to those obtained three years before.

In a sample of monozygotic twins, intrapair differences in reported birthweight were larger in those pairs discordant for later psychosis, compared to pairs concordant for psychosis. A trend towards less family history of psychiatric disorder was also found in the discordant pairs.

Certain congenital malformations occur in excess among twins and also among first-degree relatives of twins. In the general population, these anomalies are familially associated with each other, and, like twinning, familially associated with unusual brain function asymmetry. They affect structures built by fusion of bilateral embryonic halves and remodeled under major influence of neural crest mesenchyme. This conjunction of associations suggests that twinning, symmetry development, and this group of malformations might share causai elements at least some of which are heritable. The problem here is the absence of zygosity differences in these relationships, because of which they cannot be explained within the biology of twinning as it has been understood. A potential resolution is offered by way of a mechanism common to MZ and DZ twinning, involving a relationship between oocyte organization and the determination of body symmetries.

A case of 15-years old, Roman male twins affected by balanic hypospadia is reported. Previous corrective surgery had not been satisfactory, leaving both boys with a curvature of the last portion of the penis. Urographic examination, carried out upon presentation, revealed in both patients a mirror renal ectopy with fusion of the two kidneys. In both, the displaced malformed kidney is below the normally situated one. In depth examination shows: 1) that the malformation concerns not only external genitals but also internal urogenital organs because of the monolateral ectopy of the normal kidney and the malformation of the ectopic kidney in both twins; 2) that the twins are MZ and that their teratological specularity is biologically of interest.

Specularity, or mirror imaging, is a well known phenomenon in twins, particularly MZ twins. It may involve slight forms, such as handedness, or rare forms, such as those involving single organs, like the heart, which can be on the left side in one twin and on the right in the MZ cotwin. That must occur in the early embryogenetic stages, and various environmental and genetic factors may be involved. In particular, one can speculate that genetic variations in cell-adhesion molecules (CAM) and/or the late time of splitting of the conceptus to originate the two twins, may all play a role.

It is proposed that the malformations observed to occur with increased frequency in monozygotic twins are similar to the types of malformations caused by mutation in homeotic genes in animals.

A case of double bilateral renal vessels in both twins of a MZ pair is reported for the first time. Even in non-twins, the anomalies reported so far involved the inferior polar arteries in agreement with the embryological development. The two male twins, examined at the age of 14 years, had simultaneously developed a marked hypertension at the age of 7 years. Zygosity was determined by blood group and HLA analysis and various clinical tests were carried out to diagnose the condition. It is suggested that the anomaly is the result of a genetically induced early block in embryonic development.

A male twin pair, the result of 34 weeks gestation by dates, 38 weeks by estimation, was delivered at our hospital by normal vaginal delivery on 02.01.87.

The mother is a 27-year old, A,Rh+ healthy school teacher. She was married to her 33-year old, first-degree cousin in 1981. They have no family history of malformed newborns or other inherited diseases.

The first pregnancy of this gravida-four mother was in 1982 and resulted in a full-term, healthy female weighing 3.5 kg. The second pregnancy was in 1984 and resulted in a 36-weeks, alive female with occipital encephalocele, who died 12 hr after birth. It is not known if this newborn had other accompanying congenital anomalies. The third pregnancy was in 1985, and the fetus was aborted at 12 weeks gestation because of anencephaly, which was diagnosed by ultrasound.

The last pregnancy was followed at a private clinic without doing ultrasound. It was not complicated by any illness, drag intake, or X-ray exposure.

After 34 weeks of gestation, male twins were delivered by spontaneous vaginal delivery. Each one had his own placenta and umbilical cord. The first twin was a healthy male weighing 2.4 kg, with Apgar score 7/8, who was discharged home in a good general condition, and was doing well when he was seen at follow up one month later.

The second twin was a male weighing 2.15 kg, and having a length of 48 cm. We was microcephalic with a head circumference of 28 cm.