Changing trends in twinning

Birth statistics (on 13,887.943 births) from 11 Indian States indicate a fall in the dizygotic twinning rate and a rise in the monozygotic twinning rate over the decade between 1982 and 1991. These figures seem to reverse the trend of the period 1960-1982. One plausible explanation is offered by the age-data on mothers, which indicate that twins of different sex are more frequently born to mothers above the age of 35. Since extensive family planning measures have reduced the upper age-limit of mothers, the birth-rate of twins of different sex has also fallen. Due to the increased proportion of twins of the same sex, Weinberg's differential method will therefore report a decline in the dizygotic twinning rate, wherever the mean age of mothers has fallen (i.e. most mothers do not reproduce after the age of 35).

Crossed renal ectopia with pelvic lipomatosis: a new syndrome involving chromosome 1

An 18-year-old male patient is described who possesses both kidneys on one side (crossed renal ectopia), together with pelvic lipomatosis. In general, lipomatosis is benign, but here the tissue shows the rare feature of malignancy. Chromosomally, the patient is typically characterised by somatic translocations involving chromosome 1 (37% metaphases); these almost always exhibit a whole chromosome translocation with chromosome 6 (35%), although involvement of chromosome 1 with chromosome 8 is present in 2% of metaphases. Other chromosomal features encountered in Giemsa-stained and G-banded preparations from lymphocyte cultures include the prevalence of a small Y chromosome in 25% of metaphases, the presence of marker dots in 20%, and acrocentric associations in 8%-10% of metaphases. However, more than 50% of metaphases have a normal 46XY karyotype with a normal-sized Y-chromosome. Crossed renal ectopia with pelvic lipomatosis can therefore be assigned to a new syndrome characterised by a whole-chromosome translocation involving chromosomes 1 and 6.

Search for chromosomal variations among gas-exposed persons in Bhopal

A chromosomal survey using standard lymphocyte cultures employing different media and G-banding techniques was initiated in 1984. This study became particularly important following the tragic gaseous exposure of the population in Bhopal at midnight on 2 December 1984. We have been able to formulate a chromosomal profile for each person whom we have studied; during 1986-1988, 154 persons were examined twice. Among seemingly normal individuals, as many as 20% might possess some chromosomal abnormality; of these, 50% may develop, at a later date, some kind of pathological complication (such as tumours, recurrent abortion or transmission of defects to their offspring). The people exposed to methyl isocyanate have repeatedly shown Robertsonian translocations, mostly in acrocentric chromosomes 13 and 21. Other types of translocations have been studied among all exposed (53) and normal (101) persons; the involvement of chromosomes 5, 9, 11, 14 and 16 is statistically significant (P = less than 0.001). One of the major clinical symptoms is dyspnoea; we have estimated that almost all seriously dyspnoeic patients have developed at least two categories of chromosomal aberrations, one of which is Robertsonian translocation, in at least 10% metaphases. Our chromosomal survey will be of significance because we are able to identify people with chromosomal aberrations that might be correlated with future pathological consequences of the accident. The "chromosomal load" that can be sustained with an apparently normal phenotype can also be measured.

Twinning and inbreeding in India: the fraternal component

It is suggested that the rise in a population depends not only on the nu number of females per thousand males, their fecundability, and the survival of offspring (mean live births), but also on the genetic background or inbreeding status of the fetuses. Abortions and stillbirths add to the interference. A hypothetical formula has been devised (Formula: see text), where Mb = mean birth rate, G = growth percentage of population sample from preceding Census, F = inbreeding coefficient, Sa = Stillbirths + abortions, and Sr = Sex ratio. It is intriguing that the product, being termed Fraternal Component (FC), is found to be almost equal to the DZ twinning rate of the population sample. Should that be confirmed, one could perhaps estimate the DZ twinning rate by an altogether new approach.

Some blood genetic markers in the Korkus of Central India

A sample of 102 individuals from the Korkus tribe, an Australoid race inhabiting Central India, was studied for the distribution of haemoglobin and ten red cell enzyme types. Polymorphism was observed in G6P dehydrogenase, acid phosphatase, adenylate kinase and glyoxalase I types and in phosphoglucomutase subtypes. The lactate and malate dehydrogenases, glucose phosphate isomerase and superoxide dismutase systems were monomorphic. A single case of HbAS was observed. The Korkus were found to have GdA+; lower frequencies of pa, AK2, GLO1 and PGM2+ were observed in the Korkus in comparison to other related tribes and caste Hindus of the same region.

Cytogenetic effects of methyl isocyanate exposure in Bhopal

Among human survivors following the methyl isocyanate (MIC) gas tragedy the major complaints have been related to deep-seated suffocation, terrible pain in breathing, and severe ocular irritations. In order to assess the possible genetic effects we have used lymphocyte cultures and screened chromosomes by two techniques; one by looking for chromosomal aberrations and the other by estimating sister-chromatid exchange (SCE) frequencies. Both these parameters are good indicators of genetic damage in chromosomal DNA. SCE frequencies in lymphocytes have been increased more than three times in MIC-exposed persons. The results were compared to two groups of controls (one group comprising persons present in the same house; the second group of persons were chosen from distant places, 20-50 km away from the incident). Chromosomal breaks have been observed in 10 out of 14 MIC-affected people (71.4%) studied while only 6 out of 28 (21.4%) controls had chromosomal breaks. Some MIC-exposed persons had chromatin bodies in addition to the normal 46 chromosomes. These observations suggest that chromosomal DNA has been damaged.

Preliminary communication: hairy tip of nose--a new trait in males

Hairy nose tip (HNT) is reported here to be another male sex-limited trait in man. Out of 1,220 females examined, none demonstated the trait, whereas the male population frequency is estimated to be 7.35%. The age of onset is 16 years, with a greater prevalence in the age group 46-55, and declining frequency after age 55. Pedigree data do not allow discrimination among several genetic hypotheses.

Functional asymmetry in the face

The possible existence of one-sided dominance in the face, similar to the phenomena of handedness and footedness, has been investigated by studying smiling pattern, movements of the angles of mouth, winking, platysma contraction, raising and everting the upper lip with dilatation of the nostril, and vertical wrinkling of the forehead, on 300 right-handed and 30 left-handed persons. The conclusions are as follows: 1. The large majority of persons investigated do not use the two sides of face equally. 2. Facial ambilaterality is a rare feature. 3. There is no clear-cut correlation between handedness and the dominant side of the face. 4. The greater percentage (58.66%) of right-handed persons show a left-sided smile and find it more convenient to perform almost all exercises with the left side of the face. A still greater percentage (73.33%) of left-handed persons shows a right-sided smile and a better performance of all exercises with the right side of the face. The contralateral relationship of handedness to the dominant side of the face is significant in the right-handed and more so, in the left-handed persons.

Twinning in India

The incidence of twinning in India, as estimated on the basis of data from the various types of maternity centers, so as to include both urban and rural population, appears to be 15.97 per thousand (12.6 DZ, 3.3 MZ). The incidence is significantly higher in rural than urban populations (18.1 vs. 11.8 per thousand). It is suggested that this may be accompanied with a higher production of DZ, possibly opposite-sexed twins.

Studies on twins. IV. Twinning in Madhya Pradesh

The high rate of twinning in rural areas is suggested to be due to higher coefficient of inbreeding, better physical conditions of mothers on the countryside and higher mean birth order. Family data indicate the frequent role of maternal genotype in DZ twinning.

Frequency of consanguineous marriages in Madhya Pradesh

With the revision of application of terms “endogamous” and “exogamous” the inbreeding levels have been calculated from certain parts of Madhya Pradesh. Higher inbreeding levels in persons with rural background are in conformity with other workers.

Studies on twins. IV. Twinning in Madhya Pradesh

Frequency and inheritance of twinning have been studied from urban and rural parts of Madhya Pradesh. Family data conform to previous findings by other authors, for other countries, that DZ twinning is influenced by the mother's genotype.

Of special interest has been a rural family in which a female, herself a cotwin of DZ pair, married twice, each time giving birth to DZ twins.

The high rate of twinning in rural areas is suggested to be due to higher coefficient of inbreeding, better physical condition of mothers on the countryside, higher mean birth order, and higher mean age of mothers. Lack of family planning may have also played a role.