Luigi Gedda

Sleep and dream characteristics in twins.

A study of sleep and dream characteristics has been carried out by questionnaire on a sample of 77 MZ and 76 DZ same-sex twin pairs of two age groups, 6-8 and 16-18 years. Genetic effects could not be detected in the younger age group and appeared to be rather limited in the older one, possibly as a result of the limited variability of the considered variables and of the levelling influence of the common environment.

Situs viscerum specularis in monozygotic twins.

A case is reported of a 14-year old male MZ twin pair, with only one partner affected by situs viscerum inversus, whereby the condition is termed situs viscerum specularis. The high degree of mirror imaging is seen as an abnormal variation of the biological time of the cleavage giving rise to MZ twinning. Electrocardiographic findings are presented and the biological implications of the condition are discussed.

Heredity and infectious diseases: a twin study.

A concordance study of 6 infectious diseases of childhood has been carried out in a sample of 656 twin pairs classified by sex and zygosity. A new approach is proposed to estimate the respective influence of heredity and of common environment. The estimates thus obtained range from 86% hereditary component in the case of measles to 100% environmental component in the case of scarlet fever.

HUMAN MONOZYGOTIC AND PLURIZYGOTIC MULTIPLE BIRTHS: HEREDITY AND HORMONE ACTION.

The Authors take once more into consideration the problem of the hereditary nature of twinning on the basis of their own studies and of recent findings on human twinning induced by human menopausal gonadotropin (HMG). Personal studies concern 3,221 cases of twinning drawn from the special files (“Gemelloteca”) of the Mendel Institute. On the basis of this material the Authors state that the occurrence of the cases of twinning in the paternal and maternal ascendancies of the twin index cases is significantly more frequent than would be expected in proportion to the frequency of twinning events in the Italian population. This finding is in agreement with the hypothesis of the hereditary nature of the twinning phenomenon. The same material is used to compare the frequency of twinning in the paternal and maternal families of twins. The observed frequency in the maternal families is significantly higher than in paternal families in which the frequency approximates population values. This finding leads the Authors to formulate the hypothesis that the twinning trait is limited to the female sex and is presently manifested by the occurrence of twins in the next generation. Thus studies on the frequency of twinning as a hereditary phenomenon should be based on the families of the mothers of twins. Original studies also concern the 1,105 triplet sets born in Italy in the years 1952-1961. A study of the experimental and theoretical distribution of sex combinations in this triplet material allowed the Authors to prove that the experimental distribution differs from the theoretical one, based on the hypothesis of independence of the two types of zygosity (MZ and DZ). The absence of independence is considered a proof of the hereditary singleness of twinning. The Authors further take into consideration cases of twinning induced in sterile women by administration of human menopausal gonadotropin (HMG): they observe that cases reported to date seem to be limited to dizygotic or plurizygotic twinning. These findings lead the Authors to believe that in this case hypophyseal FSH, responsible for ovulation, fails to find the usual pathway leading to standard uniparous pregnancy in the human species; the mechanism involved in such pathway is the object of some hypotheses of a hormonal nature. The Authors also believe that FSH stimulates not only the follicle but also follicular gametogenesis and even perhaps the division of the fertilized egg resulting in MZ twinning.

Chronology of the Gene

1. GENETIC DETERMINATION OF BIOLOGICAL T I M E ( T H E ERGON/ CHRONON SYSTEM) 324 1.1. The Times of the Gene 324 1.2. A Scientific and Medical Problem . 325 1.3 Physical Time and Biological Time 325 1.4. The Hereditary Imprint of Biological Time 327 1.5. Variability among Species, Populations, Families, and Individuals . . 327 1.6. The Temporal Dimension of the Gene 330 1.7. Experimental Verification 331 1.8. The ErgonjChronon System . . . . 332

On a case of rare chromosomal aberration.

The Authors report a case of translocation 21/21 in a woman who, after two miscarriages, gave birth to a mongoloid daughter — dead a few days after birth. The chromosomal aberration was present in 100% of the plates examined. Occasional chromosomal alterations, found in the patients karyotype, might be held responsible of small phenotypic alterations. No alteration was found in the husbands karyotype.

The chronogenetics of caries in primary dentition.

A chronogenetic analysis of caries has been carried out in a sample of 100 twin pairs (27 MZ, 64 DZ, 9 UZ) aged 3-8 years, taking into account the number of decayed teeth and the intensity and severity of caries. Heritability estimates, calculated for each of the various parameters considered, support the hypothesis of a genetic control of the time of onset of caries.

Equivocalness and other empirical methods in zygosity assessment.

Zygosity determination is generally carried out by different methods in small or large twin samples. The probability method based on sex and genetic markers is limited to relatively small samples, as a consequence of its cost. The empirical questionnaire method is applied in several large twin registers. Its margin of error is low enough for population studies, its cost is negligible, but its accuracy is insufficient when zygosity of twin pairs included in definite samples must be individually assessed. Efforts to bridge the distance between the two methods should be made, and they may take either direction: (1) find new, inexpensive genetic markers, or (2) increase the number and accuracy of empirical methods. The accuracy of a number of empirical methods applied to a twin sample of established zygosity has been compared. One modification of the “two peas in a pod” method, originally called “equivocalness method”, appears to warrant inclusion in questionnaire methodology. Also, compound probability as expressed by several empirical methods may reach an acceptable level of accuracy in zygosity assessment.

Chronological Development of Bones and Teeth A twin study

The hereditary component of the chronological development of bones and teeth has been studied, in 40 twin pairs aged 5-7 years, through dental age (defined on account of the mineralization of the permanent dentitions dental buds) and bone age (denned on account of the presence and form of the hand ossification nuclei). The statistical analysis shows a correlation coefficient of 0.95 in MZ and 0.84 in DZ twins for dental age; and of 0.94 in MZ and 0.81 in DZ twins for bone age. The following are therefore the estimates of the hereditary component (based on Holzingers formula) for the two parameters studied:

Computerization of a Permanent Twin Register: a Basic Tool in Scientific Research

The Authors report on the steps involved in the computerization (coding of data, card punching and tape recording) of a Twin Register initiated in 1942 and currently approaching 11,000 cases of multiple births. The Register is permanent in that it involves continued updating of information and addition of new cases. It includes twins of any age, sex, zygosity and health condition. The experience gained in the reported project can be usefully shared in wiew of international cooperation and standardization.