Twin Study Method Research Articles

Contributions of Nicholas Martin to Gambling Disorder Research.

Professor Nicholas G. Martin, from QIMR Berghofer Medical Research Institute in Brisbane, Australia, is a world leader in the effort to understand the genetic architecture underlying disordered gambling. This article pays tribute to Nick and his almost two decades of gambling research, highlighting his many strengths, ranging from the use of ingenious recruitment approaches, twin study methods, genomewide association studies, to facilitating international collaborations.

The Developmental Nature of the Victim-Offender Overlap

PurposeIt is well-established that victims and offenders are often the same people, a phenomenon known as the victim-offender overlap, but the developmental nature of this overlap remains uncertain. In this study, we drew from a developmental theoretical framework to test effects of genetics, individual characteristics, and routine-activity-based risks. Drawing from developmental literature, we additionally tested the effect of an accumulation of adverse childhood experiences (ACEs).MethodsData came from the Environmental Risk (E-Risk) Study, a representative UK birth cohort of 2232 twins born in 1994–1995 and followed to age 18 (with 93% retention). Crime victimization and offending were assessed through self-reports at age 18 (but findings replicated using crime records). We used the classical twin study method to decompose variance in the victim-offender overlap into genetic and environmental components. We used logistic regression to test the effects of childhood risk factors.ResultsIn contrast to past twin studies, we found that environment (as well as genes) contributed to the victim-offender overlap. Our logistic regression results showed that childhood low self-control and childhood antisocial behavior nearly doubled the odds of becoming a victim-offender, compared to a victim-only or an offender-only. Each additional ACE increased the odds of becoming a victim-offender, compared to a victim-only or an offender-only, by approximately 12%, pointing to the importance of cumulative childhood adversity.ConclusionsThis study showed that the victim-offender overlap is, at least partially, developmental in nature and predictable from personal childhood characteristics and an accumulation of many adverse childhood experiences.

Heritability of Thirty Cephalometric Parameters on Monozygotic and Dizygotic Twins: Twin Study Method

Genetic mechanisms are already predominant during embryonic craniofacial morphogenesis, but environment is also thought to influence dentofacial morphology postnatally, particularly during facial growth. A better understanding of the relative effects of genes and environment on dentofacial and occlusal parameters should improve our knowledge on the etiology of orthodontic disorders and therefore also on the possibilities and limitations of the orthodontic treatment and treatment planning. The aim of the present study is to explore the genetic and environmental influence on craniofacial dimensions in a group of 19 pairs of twins using the twin study method. The twin study carried out here clearly indicates that craniofacial matrix is under substantial genetic control and the redirection of a basic growth pattern may be modified only within biological limits which are harmonious for the patient.

Mapping Heritability and Molecular Genetic Associations With Cortical Features Using Probabilistic Brain Atlases: Methods and Applications to Schizophrenia

There is an urgent need to decipher the complex nature of genotype-phenotype relationships within the multiple dimensions of brain structure and function that are compromised in neuropsychiatric syndromes such as schizophrenia. Doing so requires sophisticated methodologies to represent population variability in neural traits and to probe their heritable and molecular genetic bases. We have recently developed and applied computational algorithms to map the heritability of, as well as genetic linkage and association to, neural features encoded using brain imaging in the context of three-dimensional (3D), populationbased, statistical brain atlases. One set of algorithms builds on our prior work using classical twin study methods to estimate heritability by fitting biometrical models for additive genetic, unique, and common environmental influences. Another set of algorithms performs regression-based (Haseman-Elston) identical-bydescent linkage analysis and genetic association analysis of DNA polymorphisms in relation to neural traits of interest in the same 3D population-based brain atlas format. We demonstrate these approaches using samples of healthy monozygotic (MZ) and dizygotic (DZ) twin pairs, as well as MZ and DZ twin pairs discordant for schizophrenia, but the methods can be generalized to other classes of relatives and to other diseases. The results confirm prior evidence of genetic influences on gray matter density in frontal brain regions. They also provide converging evidence that the chromosome 1q42 region is relevant to schizophrenia by demonstrating linkage and association of markers of the Transelin-Associated-Factor-X and Disrupted-In- Schizophrenia-1 genes with prefrontal cortical gray matter deficits in twins discordant for schizophrenia.

Psychiatric morbidity in adult survivors of childhood trauma.

This review focuses on child sexual abuse (CSA) as a prototype of childhood trauma and evaluates the evidence on psychiatric morbidity in adult survivors. An association between CSA and a wide range of psychiatric morbidity has been consistently documented in general population studies. The interpretation of this observed association is fraught with uncertainty that stems primarily from: (1) the retrospective nature of the data on CSA from adults' reports on their early experiences; (2) the adverse family context in which it occurs, which presents a major challenge for evaluating the effect of CSA per se; (3) the well documented lifetime comorbidity among psychiatric disorders, which leaves open questions about the specificity of CSA outcomes in adulthood. Twin study methods offer a solution to the problem of the familial context of CSA. Ascertainment of age of onset of adult disorders in future studies would increase the utility of findings for formulating psychological and biological causal models on the CSA-adult disorders connection. However, the retrospective nature of data on child abuse, because of legal and ethical restraints on research on children, is a formidable obstacle to advancing knowledge in this field.

Essential tremor in twins: an assessment of genetic vs environmental determinants of etiology.

To determine the relative contribution of genetics and environment to essential tremor using a twin study method. Twins with postural or kinetic tremor were identified by movement disorders specialists during the conduct of a study investigating PD in members of the National Academy of Sciences and National Research Council World War II Veteran Twins Registry. The diagnosis of essential tremor was made by consensus using established diagnostic criteria. A total of 196 twins had postural or kinetic tremor on examination. Of these, 137 had PD or had a twin with PD and were excluded from this study. Thirty-three others were excluded because of incomplete data for their twin. Sixteen twin pairs were identified in which at least one twin had essential tremor. Pairwise concordance in monozygotic twins was approximately two times that in dizygotic twins (0.60 monozygotic, 0.27 dizygotic). This pattern is consistent with a genetic cause of essential tremor. Because monozygotic concordance is not 100%, environmental factors may also play a role in the cause of the disease.

Twin study using mortality data: a new sampling method.

To evaluate the success of a novel approach to twin studies using death discordant twin pairs in a disease of low prevalence. A population study based on all registered deaths at the Office of Population Censuses and Surveys of England and Wales, classified under the ICD code 335.2 (motor neuron disease [MND]) for the period 1979-1989 inclusive. From the above database of 10,872 people, individuals born after 31 December 1899 were traced in the Birth Indices for England & Wales to enable identification of possible twins. In all 131 twin pairs were found and the co-twin details were sent to the National Health Service Central Register (NHS-CR) to enable location of the relevant Family Health Services Authority and thence the co-twin's general practitioner (GP). A letter requesting access was sent to the family practitioners. If given, the co-twin can be approached and interviewed. The search produced: 54 living co-twins; 31 who died as adults; 29 infant deaths; 5 emigrated; 3 incorrectly diagnosed index twins; and 9 untraceable co-twins. Among the adult deaths two concordant pairs were identified. This has created the largest twin population sample worldwide for MND. This new twin study method is clearly viable, and has produced a large unbiased sample compared to that possible using traditional methods. It relies heavily on the accuracy of death certificates and zygosity reporting by living co-twins, but is possibly the only way of collecting twins in rare conditions.

The genetic theory of schizophrenia. An analysis of 691 schizophrenic twin index families. 1946 [classical article

1. The methods available for genetic investigations in man are the pedigree or family history method, the contingency method of statistical prediction, and the twin study method. 2. A study of the relative effects of hereditary and environmental factors in the development and outcome of schizophrenia was undertaken by means of the "Twin Family Method." The study was organized with the cooperation of all mental hospitals under the supervision of the New York State Department of Mental Hygiene. The total number of schizophrenic twin index cases, whose cotwins were available for examination at the age of fifteen years, was 794. 3. In addition to 1,382 twins, the 691 twin index families used for statistical analysis include 2,741 full siblings, 134 half-siblings, 74 step-siblings, 1,191 parents, and 254 marriage partners of twin patients. The random sampling of these twin index pairs is indicated by the distribution of 174 monozygotic and 517 dizygotic pairs, yielding a ratio of about 1 : 3. 4. The morbidity rates obtained with the "Abridged Weinberg Method" are in line with the genetic theory of schizophrenia. They amount to 1.8 percent for the stepsiblings; 2.1 percent for the marriage partners; 7.0 percent for the half-siblings 9.2 percent for the parents; 14.3 percent for the full-siblings; 14.7 percent for the dizygotic cotwins; and 85.8 percent for the monozygotic cotwins. This morbidity distribution indicates that the chance of developing schizophrenia in comparable environments increases in proportion to the degree of blood relationship to a schizophrenic index case. 5. The differences in morbidity among the various sibship groups of the index families cannot be explained by a simple correlation between closeness of blood relationship and increasing similarity in environment. The morbidity rates for opposite-sexed and same-sexed two-egg twin partners vary only from 10.3 to 17.6 percent, and those for non-separated and separated one-egg twin partners from 77.6 to 91.5 percent. The difference in morbidity between dizygotic and monozygotic cotwins approximates the ratio of 1 : 6. An analysis of common environmental factors before and after birth excludes the possibility of explaining this difference on non-genetic grounds. 6. The difference between dizygotic and monozygotic cotwins increases to a ratio of 1 : 55, if the similarities in the course and outcome of schizophrenia are taken as additional criteria of comparison. This finding indicates that constitutional inability to resist the progression of a schizophrenic psychosis is determined by a genetic mechanism which seems to be non-specific and multifactorial. 7. The predisposition to schizophrenia, that is, the ability to respond to certain stimuli with a schizophrenic type of reaction, depends on the presence of a specific genetic factor which is probably recessive and autosomal. 8. The genetic theory of schizophrenia does not invalidate any psychological theories of a descriptive or analytical nature. It is equally compatible with the psychiatric concept that schizophrenia can be prevented as well as cured.

歯・顎顔面頭蓋形態における遺伝的および環境的特徴 中南米での海外学術調査資料を用いて

Most previous researches of hereditary characteristics of the craniofacial skeleton have used the twin-study method. In this study, dental anthropological materials were used to clarify genetic and environmental characteristics of the dento-craniofacial morphology. The sample consisted of four groups including Mexican Indians (N = 71), Peruvian Indians (N = 41) and their ancient ancestors: skulls of Mexican Indians (N = 33) and Peruvian Indians (N = 34). These groups shared the common origin of the Mongoloid race. Morphological similarity and difference among these groups were examined by principal component analysis and Student t-test using the dento-craniofacial data based on roentgenographic cephalograms and dental casts. The morphological similarity means the genetic characteristics which maintained during time differences between ancient and present times and throughout regional differences between Mexico and Peru. The morphological difference means the environmental characteristics which produced during the time differences and throughout the regional differences. Results were as follows: (1) The genetic morphological characteristics were found predominantly in the anterior cranial base, the dental arch form and to a certain extent in the basal portion of the mandible and the vertical dimension of the naso-maxillary complex. (2) The environmental characteristics were found predominantly in the muscular portion of the mandible, the alveolar portions of the maxilla and the mandible, the length of the dental arch and to a certain extent in the antero-posterior dimension of the maxilla.

Genetic variance estimates and familial resemblance for body size traits.

To study genetic contribution to complex body size traits, the intrafamilial correlation and regression analyses along with twin study method have been used. The data are based on a sample of 45 MZ and 101 DZ twin pairs, their 125 singleton siblings, 104 fathers and 103 mothers in 146 Punjabi families living in Chandigarh, India. Twin study gives no evidence of inequality of means and variances between zygosities. Within-pair genetic variance ratios, correlations, regressions of offspring on midparent and single parent are all significant at 0.1%, thus indicating strong genetic component. Heritability estimates are higher for longitudinal body traits than the breadth dimensions. The resemblance of the children with the parents of either sex is not equal. Higher maternal influence is indicated for a number of body traits. The results on familial correlations do not support the hypothesis of sex-linked inheritance for any of the traits considered in this investigation. These results have been compared with those from other such studies.

Genetic and environmental influences on the development of piagetian logico-mathematical concepts and other specific cognitive abilities: a twin study.

The classical twin study method was used to assess the relative contributions of genetic and environmental components to individual variation in several aspects of cognitive functioning. Tests of logico-mathematical concept formation, as well as vocabulary, nonverbal reasoning, and visual memory, were administered to 137 MZ and 72 DZ, same-sex white twin pairs. These children were individually tested on the Piagetian Mathematical Concepts Battery (PMCB), Peabody Picture Vocabulary Test (PPVT), Raven Coloured Progressive Matrices (PM), and a Visual Memory (VM) test. The Attitudes Toward Education (ATE) questionnaire and the Moos [63] Family Environment Scale (FES) were used to collect additional data from the parents. Twins were 4 to 8 years old, with a mean age of 71 months, and most were from middle- and upper-middle-class families. Zygosity was determined from dermatoglyphic information and responses to a questionnaire asking mothers about twin similarities and confusion between the twins by others. These data were analyzed by a simple pair concordance procedure and by a discriminant function analysis. In addition, blood typing was done on 32 pairs for whom zygosity was not possible to determine by these methods.Previously reported patterns of intercorrelations among the 10 subscales of the FES, as well as the subscale structure, were verified by factor analysis. A factor analysis of the ATE yielded three factors: Basic Academic Education, Parental Participation, and General Utility of Education. These factors correlated significantly (P < 0.01) with various environmental indices (including father's occupation and education, Achievement Orientation, Expressiveness, etc). A factor analysis of the PMCB tasks gave some support for the existence of Piaget's underlying concepts of conservation of number, seriation, and classification.No sex differences were found for any of the specific cognitive abilities or any of the environmental variables. Correlations with age were substantial: 0.75 for PMCB, 0.70 for PPVT, 0.59 for PM, and 0.43 for VM. Because of the high correlations with age, the effect of age on these variables was partialed out in all further analyses. PMCB correlated most highly with PM (r = 0.41), and with PPVT (r = 0.36). Nonverbal reasoning and vocabulary were relatively independent of each other (r = 0.23). Correlations between visual memory and all other tests were low.MZ and DZ intraclass correlations for height and weight were similar to values reported in other studies. After correcting for test reliability, significant genetic variance (P < 0.01) was found for both PMCB and PPVT, and was suggested for VM. Genetic variance for PM was not significant (P > 0.05). Correction for reliability could not be employed in this case because an accurate estimate of the PM test–retest reliability is not available. There was no significant effect of age on the magnitude of the MZ or DZ intraclass correlations.A stepwise multiple regression on the environmental variables was performed for each cognitive test. The environmental variables considered were number of siblings, parental education and occupation, the 10 FES subscales, and the three ATE factors. Age was entered first in the regression equation for each test, and it accounted for 18% to 57% of the total variance in cognitive performance. Parental education accounted for 3% of the total variance in both PMCB and PPVT performance. This was considered as an environmental influence, but the possible confounding with a genetic element in parental IQ was discussed. Achievement Orientation exhibited a significant negative relationship (R2= 0.02) with PM performance. Cohesion in the Family was positively related to PPVT performance (R2= 0.02). In addition, Intellectual–Cultural Orientation predicted VM performance (R2= 0.02). Overall, those environmental variables found to have a small effect suggest the value of a warm, stimulating, supportive (but not “pushy”) family environment for normal cognitive development in young children.Examination of the genetic and environmental results indicated that 49% of the variance in age-corrected PMCB performance was accounted for by the genetic variance (estimated from twin comparisons) and parental education. Similarly, variables identified in this investigation accounted for 60% of the variance in age-corrected PPVT performance, 29% of the age-corrected PM performance, and 32% of age-corrected VM performance.In conclusion, this was the first large twin study to find both genetic and environmental influences on the development of Piagetian logico-mathematical concepts and other specific cognitive abilities. The results illustrate the feasibility of investigating cognitive development in a theoretical framework such as Piaget's.

Twin method: Defense of a critical assumption

Since Galton's time, critics of the twin method have rejected the evidence of genetic differences in human behavior, because the twin method assumes that identical and fraternal pairs have equally similar environments. Twins whose genetic similarity is misperceived by themselves and others provide a critical test of the adequacy of this assumption. The relative effects of perceived and actual genetic similarity on cotwin differences in cognitive, personality, and physical development were assessed in a sample of young, adolescent twins whose genetic similarity was often misperceived. Twins' responses to questions about their own and others' judgments about their zygosity and physical similarity, and the ratings of similarity by eight judges, were used to estimate the perceived similarity of the twins. Actual zygosity was established by matching cotwins on 12 or more blood group loci. Perceived zygosity and perceived similarity by self and others were found to be insignificant biases in the twin study method.

Genetic determinant of lithium ion distribution. I. An in vitro monozygotic-dizygotic twin study.

Research in pharmacogenetics has provided evidence that individual variation in rate of metabolism of various drugs is genetically controlled. To evaluate the possibility of a genetic determinant of lithium ion distribution, a monozygotic (MZ)-dizygotic (DZ) twin study method was used. Red blood cell (RBC) lithium ion concentrations were assessed for ten MZ and seven DZ twin pairs following a 24-hour incubation in vitro. The distributions of intrapair difference scores of MZ twin pairs and DZ twin pairs were relatively nonoverlapping, with MZ intrapair difference scores being smaller on the average. A heritability index of 0.85, calculated as a function of intrapair difference scores, indicated that a substantial genetic factor is operative in RBC uptake of lithium ion.

The pathogenesis of schizophrenia. Possible relationships between genetic, biochemical, and experiential factors.

A series of studies in schizophrenia, using several varieties of the twin study method, are reviewed and five major conclusions or hypotheses drawn. A modified twin study design—the co-twin comparison method—is described, with which these conclusions and hypotheses can be tested; and two additional major issues—specificity to schizophrenia, and the antecedent-consequent question—dealt with. A stress model of schizophrenia pathogenesis is presented, which attempts to integrate genetic, biochemical, and experiential variables.

The Twin-Study Method in Medicine and Genetics

The twin-study method has contributed greatly to our knowledge of the interrelationships of heredity and environment. Studies of monozygotic twins reared together and apart and studies of concordance for certain traits in monozygotic and in dizygotic twins are reviewed.

Influence of early physical conditions on the development of intelligence, with special reference to the analysis of monozygotic twins

The twin study method is deemed to be the most reliable one in order to study the hereditary and environmental influences upon the development of intelligence. Among the various conditions the problem of early physical conditions was this time taken up, using individual intelligence test scores obtained from 269 pairs of monozygotic (MZ) twins and 64 pairs of same-sexed dizygotic (DZ) twins, all twelve years of age. Among the results obtained, the statistically significant ones were as follows:I. The analysis of the physical conditions compared between MZ and DZ twins indicated that MZ twins showed much more similar birth weights, a shorter time interval in birth, and less difference in the initiation of walking than DZ twins. As to MZ twins with a great difference in the start of walking, it was found that the first-born, or the heavier twin began to walk earlier than the other twin, while this relationship could not be seen in DZ twins.II. The view of many previous researchers that MZ twins as a whole show higher degree of conformity in the development of intelligence than DZ twins was not supported by all cases of our MZ twins, and in some MZ twins a great difference of intelligence was found. This difference was considered having been caused by the environmental factors.III. Those MZ twins who showed a great intra-pair difference in their biological conditions at birth were selected. The comparative analysis of the data indicated that1) as to pairs with a great intra-pair difference in birth weight, the heavier twin showed the higher intelligence score, 2) as to pairs with a long intra-pair interval in birth, the first born showed the higher score, 3) when a twin was born with asphyxia neonatorum, he showed a lower score, and4) those twins who showed a great difference in intelligence scores also showed a difference in their initiation of walking and/or talking.Although there was a tendency that MZ twins were born with much more similar physical conditions than DZ twin, there was a great intra-pair difference observed in the development of intelligence at the age of twelve if MZ twins passed through different physical conditions at birth. A definite relationship between the early physical conditions and the intelligence development was thus illustrated, that is, the MZ twin born with superior conditions generally showed superiority in the development of intelligence.

An investigation of craniofacial asymmetry using the serial twin-study method

In certain cases, asymmetry of the craniofacial complex can be a problem of concern to the orthodontist, in both diagnostic and treatment procedures. Few studies have been made of this problem, the main reason being the lack of a suitable tool for the accurate measurement of right-left differences in three planes of space. By the application of solid geometry design for correction of size distortion, the two-film roentgenographic cephalometric technique introduced by Broadbent 6 has been used to record measurements of right and left structures within the craniofacial complex. By suitable mathematical treatment, the two-film procedure yields three-dimensional distances, thereby expressing both form and position of right and left structures. On the basis of recent findings regarding the relative stability of certain cranial and extracranial points, three registration points were selected, and distances from them to appropriate right and left structures were calculated. Values for both right and left sides were secured (1) relative to the cranial base, (2) for those within the maxilla, relative to anterior nasal spine, and (3) for those within the mandible, relative to the mandibular point, menton. Indexes were constructed which could be comparable both in time and within the sample on an individual-to-individual basis. Cross-sectional indexes represented observations at two particular moments in time, 1957 and 1960. Serial indexes included the interval between these two times, reflecting incremental changes in terms of asymmetry. By retention of the appropriate arithmetical sign, the preservation of direction of change, if any, was recorded. The sample employed in this study consisted of six same-sex sets of triplets of North American Caucasian descent, aged 9 to 15 years. By within-set pairings, six identical twin sets and twelve fraternal twin sets were secured. Through the use of serial records, taken in 1957 and again in 1960, and employing the twin-study method, many questions could be investigated with a small sample that could not be answered satisfactorily with a large population sample: 1. 1. Are craniofacial asymmetries predominantly controlled by heredity? Or is environment more influential in the production of rightleft differences? 2. 2. Do all regions of the craniofacial complex exhibit the same degree of asymmetry? Or, for example, is asymmetry of the maxillary region greater than asymmetry of the mandible? 3. 3. Is degree of asymmetry constantly proportional throughout the development of the individual? Or does the difference between right and left sides undergo changes with age? 4. 4. What are the ranges or limits of asymmetry in the craniofacial complex? To answer these questions, the data were then subjected to statistical treatment which permitted interpretation of possible differences (1) between identical and fraternal twin members, (2) between age groupings, (3) between times of observation, and (4) between regions within the craniofacial complex. The main statistical procedure used was multifactorial analysis of variance. Once differences were recognized, additional treatment was performed to determine means, ranges, and standard deviations. Means were then tested against each other to identify those which were truly different and those whose difference was small enough to have occurred by chance in the sampling process. The findings of this study were as follows: 1. 1. Regardless of method of analysis, I have failed to show significant differences between identical- and fraternal-twin groups. Thus, according to this study, heredity is not the controlling agent in the production of craniofacial asymmetry (excluding hereditary syndromes). 2. 2. Cross-sectional evaluation shows that there are decided differences in amounts of asymmetry of the various craniofacial regions and landmarks, but serial evaluation shows no differences. Therefore, although there may be initial differences between right and left sides, these differences are not intensified with dimensional changes occurring with increase in age. 3. 3. Although age differences of mean asymmetry exist on a cross-sectional basis, there is no effect of age on the individual's mean asymmetry (when measured serially). 4. 4. Ranges or limits of asymmetry have been established for the various craniofacial landmarks included in this study. An approach which utilizes conventional oriented lateral and posteroanterior roentgenograms for the measurement of craniofacial asymmetry has been offered. This procedure has been applied to answer basic questions concerning the nature of asymmetry. Three-dimensional assessment of gross asymmetries, such as cleft lip and cleft palate, condylar and facial dysplasia, and craniofacial hereditary syndromes, can now be made. Moreover, pretreatment and posttreatment evaluation can be made of those patients with gross asymmetries who would seek orthodontic, surgical, or prosthetic treatment.

THE INTERACTION OF HEREDITARY AND ENVIRONMENTAL INFLUENCES1

This paper is concerned with improvements in the multiple abstract variance analysis method (MAVA). The assumptions of the latter are more clearly developed and implications for genetic, psychological, and sociological research issues are discussed. The main conclusion is that although it offers solutions to questions not answerable by twin study methods, or by current experimental designs related to learning theory, to personality theory and to important sociological issues, MAVA demands much larger and more carefully planned and highly organized research programmes than have hitherto been contemplated in psychology.

An investigation of craniofacial asymmetry using the serial twin-study method: By James F. Mulick, A.B., D.D.S., University of Washington, Seatle, Washington

An investigation of craniofacial asymmetry using the serial twin-study method: By James F. Mulick, A.B., D.D.S., University of Washington, Seatle, Washington

Il « metodo clinico-gemellare » nel rilievo del sintomo radiologico della stasi cerebrale e dell'influsso negativo delle cardiopatie sullo sviluppo corporeo (3 coppie MZ cardiopatiche discordanti)

SUMMARYThe Author reports two MZ twin pairs, one of 11 years old females and one of 18 years old males, only one twin in each pair being affected by severe cardiac failure. In both cases the cranial radiograph of the hyposystolic twin, compared with that of the co-twin, revealed the existence of cereblar stasis.The Author also reports on two female MZ pairs of developmental age, each with one cardiopathic twin. In both cases the affected twin revealed a retarded body development and, in one pair, also retarded puberty.The Author stresses how the twin study method is helpful in clinical as well as genetical research, thus reasserting its validity.