MZ Co-twins Research Articles

A Twin Study on the Heritability of Lipoprotein Fractions

Volunteer adult twins (aged 18-65), after a 12-hour fast, provide two 15 ml samples of blood for analysis by Auto Analyzer II, by agarose electrophoresis and by direct gas chromatography. Provisional diagnosis of zygosity is based on subjects' own opinions, supported by dermatoglyphic analysis and, in any difficult case, substantiated by an enzymatic series. Analysis of the AA-II and electrophoresis data on the first 2 × 45 subjects shows a significant positive correlation within MZ pairs for each of the 7 lipid measurements considered, while the estimate of correlation within DZ pairs is lower in every case. Heritability appears to be higher for cholesterol than for triglyceride fractions. The electrophoretic band for the sinking pre-beta lipoprotein fractions has behaved like a simple genetic marker. Interrelationships among different lipoprotein fractions are studied in terms both of phenotypic and genetic correlations, both of which confirm the expected positive association between amounts of triglyceride and of cholesterol in the supernatant (Sf > 20), and both also show negative correlation between the pre-beta and the alpha fractions. Another aspect of the analysis is the study of lipid differences between MZ cotwins in relation to corresponding intrapair differences in body weight and medical history; male, but not female pairs, show a measurable statistical dependence of cholesterol and triglyceride levels on « excess » body weight.

A contribution to the psychological study of interpersonal relations in twins.

A sample of 71 pairs (32 MZ, 39 DZ), of mean age 9.7 years, has been studied through various techniques in order to better understanding the interpersonal relation of twins, both within the pair and with repect to the members of the family group, and especially the mother. Zygosity, dominance, and birth order have been taken into account. The relation between MZ twins appears to be somehow less special than believed, whereas a special triadic relation appears to exist with the mother. A differentiated research of identity in MZs and autonomy in DZs is also noted (which contributes to a better understanding of problems of schizophrenia in twins). Finally, the relation between MZ cotwins shows mutual similarity and attachment to be lower than foreseen and, anyhow, of a far from mysterious nature.

Physical and Intellectual Evolution of MZ Cotwins with Discordant Birth Weight

Physical and Intellectual Evolution of MZ Cotwins with Discordant Birth Weight

Twenty-one psychiatric cases and their MZ cotwins. A thirty years' follow-up.

In 1941, I published a psychiatric study of 69 same-sexed pairs of twins. The index cases were derived from 8596 consecutive admissions to three mental hospitals and one psychiatric unit of a general hospital in South Sweden, every patient being checked for twin birth in the official birth registers. There was no pair with more than one index case. Upon examination, 21 pairs were considered more or less certainly MZ, and 48 DZ. The degree of certainty of the zygosity diagnosis was expressed by a special formula (Essen-Möller, 1941b).Of the 21 index cases, 7 (N. 1-7 of the monograph) were at that time judged schizophrenic. The later course revaled that one more index case (N. 12) was a schizophrenic and should have been included into this diagnostic group, which I shall have to concentrate upon in this brief presentation.Out of the 8 cotwins of the schizophrenic index cases, 5 had presented symptoms of mental disorder up to the time of my investigation, which took place almost thirty years ago. This corresponds so far to a concordance rate of 62%. However, all of the cotwin disorders were relatively mild and transient in nature and consisted mainly of depressive or anxiety states. Even if some of the disordered cotwins had spent some time in a nursing home or in a psychiatric ward of a general hospital, none of them had been admitted to a mental hospital. And, although several of the clinical pictures contained some single trait suggestive of schizophrenia — such as ideas of reference (N. 2 and 7) or hallucinations (N. 5) — in no case a proper diagnosis of schizophrenia could be made. The cotwin who came closest to this diagnosis was a man aged 35 (N. 1), who gave much thought to telepathic phenomena and the like; yet, he was comparatively open-minded and accessible to discussion of his ideas, and he had never been incapacitated by them. Thus, at the time of the first investigation, the correct rate of concordance for schizophrenia in fact was zero. This finding was the more striking as the two other samples published up to that time, those of Luxenburger (1928) and Rosanoff (1934), showed rates of concordance at about 70%, although Luxenburger (1934) later corrected his figure to 33%, for diagnostic reasons. Personally, I was inclined to attribute my zero finding to chance, the number of pairs being small, and also to the relatively short time of observation.

Electroencephalographic findings in MZ twin pairs, discordant for closed head injury.

SummaryA follow-up EEG study in 28 cases with closed head injuries, using MZ co-twins as controls, is described. A new concept in EEG analysis is introduced. A combined EEG code and point scale are more effective in discriminating subtle differences between two EEG records. A high concordance was found whether the EEG showed normal or abnormal patterns. Not only the head-injured twins but also the controls showed more abnormalities than in the normal population. Without this check by co-twins the EEG abnormalities could have been taken for persisting signs of the proband injury. It was found, however, in late follow-up that proband twins showed more EEG aberrations and abnormalities than co-twins, but the probands differed already in pre-traumatic mental make-up from their genetically identical controls. Neither differences in mental make-up nor in EEG characteristics showed any statistically significant correlation with the severity of the proband injury. These observations limit the significance of EEG abnormalities in late concussional states.This study also indicates that there are individually specific EEG patterns, which in health retain their characteristics throughout life. The EEG pattern is therefore concordant in identical twins. Thus, when a twin is influenced by a brain disease or lesion, the co-twin may serve as a biological control in both acute and follow-up studies.

GENETIC FACTORS IN ACTIVITY MOTIVATION

A study of 61 pairs of identical (MZ) and fraternal (DZ) grade-school twin girls found moderate genetic contributions to individual differences in several aspects of activity motivation: reaction time, variety of activity, anxiety, and impatience. Activity motivation was defined by empirical clusters of related measures including ratings, experimental tasks, and interviews. Intraclass correlation coeficients for the MZ and DZ groups were compared, and heritability estimates were computed for every measure. Possible biases in twin research were examined with special emphasis on the environmental similarity of MZ and DZ co-twins.

Dental diseases, malformations and malpositions studied with the Twin Clinical Test

SUMMARYThe Twin Clinical Method (Gedda, 1963) has been applied to the study of dental pathology. Four cases of MZ female twin pairs have been studied, concordantly affected by dental agenesis (case I), mirror-imaging dental agenesis (case II), diastema (case III), and dental caries and enamel dystrophy (case IV). The test has also been applied, and for the first time, to a set of MZ female triplets, concordantly affected by dental caries and malposition.In all the above cases, the test has permitted to reject hypothesis of a concordance being due to chance, while postulating the existence of a causality.The latter is ascribed to the common heredity characterizing MZ cotwins.

Sindrome di Werdnig-Hoffmann familiare che include una coppia di gemelli MZ concordanti (un caso di Consulenza Eugenica)

SUMMARYThe Authors report the eugenic prediction formulated for a couple whose three babies (two of whom were monozygotic twins) had died as a consequence of the syndrome of Werdnig-Hoffmann. Since the two cases of the MZ twin pair represent a single chance combination at conception, and since the indications from the literature and from the family tree in this case indicate a monomeric genotype of a recessive type, the morbid risk for a fourth affected child has been estimated at 25%.The occurrence of concordant W. H. syndrome in MZ cotwins is stressed.No chromosome abnormalities have been revealed by karyotype examination of the parents.