[Monozygous female twins discordant for a pattern of X chromosome inactivation as a model for study on X-linked intellectual traits]

Ring the last decades, numerous genes for general cognitive ability were identified on human X-chromosome. They were discovered primarily because of X-linked mutations causing nonspecific mental retardation in males. Evidence for imprinted loci on the X chromosome affecting neurodevelopment was found in studies on 45,X females. Investigation of transmission of X-linked traits in normal individuals might further contribute to problem of shaping human being's mind ability. We suggest monozygous female twins discordant for a parent-of-origin of the X chromosome inactivation to be a proper subject for such explorations.

[Anorexia nervosa variants and their correction]

124 girls with anorexia nervosa were investigated. Two types of anorexia nervosa course were revealed. The disease takes its benign course, without derangement of social adaptation in patients having strain of hysteria; those with schizoid stigmas have food reaction abnormality as a debut of schizophrenia.

[Variation of bacterioplankton number in the north-western part of the Black Sea depending on hydrological and hydrochemical factors]

Quantitative analysis of total bacteria numbers variations under influence of river outflow and development of anaerobic conditions has been carried out on the basis of long-term field research in the north-western part of the Black Sea. The regressive equations describing dependence of the total bacteria number on temperature, salinity and water saturation with oxygen have been calculated. These results allow to characterize more completely the regularities of eutrophication processes on the Black Sea shelf.

[Results of estimation of mutation rates for translocation trisomy 21]

Among 1332 cases of trisomy 21 born within 1979-1999 in St. Petersburg, 76(5.7%) were carriers of a translocation between chromosome 21 and other acrocentrics. Among 43 Dq; 21q translocations, 17 were inherited from the mother, and one was inherited from the father, 16 were of sporadic occurrence, and in 9 cases the mode of inheritance was not established. Out of 31 cases displaying Gq;21 translocation, 23 were mutants and 8 of unknown origin. One case of non-Robertsonian translocation 21;22 was maternal in origin. It was assumed that the proportion of sporadic cases among translocations of unknown origin is the same as that among translocations of the known origin. However, it is conceivable that the parents of a child with a sporadic anomaly, previously having an uncomplicated reproductive history and healthy children, tend to avoid cytogenetic examination more often than the carriers of translocation. Hence, the reported proportion of de novo cases (-0.6) might be underestimated. The analysis of pregnancy outcomes in mothers of children with Down syndrome, who inherited translocation (n = 12), sporadic translocation (n = 12) and translocation of unknown origin (n = 8), supports this suggestion. Analysis of the data from 8 reports, where the origin of Dq;21 was specified, revealed that in those samples, where the origin was traced in almost all families, the proportion of de novo cases (0.75-0.82) was higher than in samples where an appreciable part of families was not examined (0.46-0.73). Therefore, with the aim of correct determination of mutation rate for Dq;21 translocation, the true proportions in D;21 cases merit evaluation. Meanwhile, using average estimation from all the above mentioned reports (0.67), the mutation rate for translocations Dq;21 in St. Petersburg was calculated to be 1.2 x 10(-5) and 0.8 x 10(-5) in 1980-1989 and 1990-1999, respectively. For Gq;21 translocations/isochromosomes, the corresponding figures were 1.6 x 10(-5) and 1.5 x 10(-5).

[Chromosome 21 mosaicism. A review]

Despite the great efforts contributed to studies on the trisomy 21 etiology, basic mechanisms of nondisjunction are still poorly understood. Even less is known about mosaic variant of trisonomy 21. In this paper, some problems of masaicism are considered: (1) estimation of the prevalence of mosaicism in patients affected with Down syndrome, (2) determination of population rate of parental mosaicism, (3) evaluation of the role of ovarian mosaicism in etiology of Down syndrome, (4) origin of the extra chromosome, (5) mechanisms of production of mosaic lines, (6) phenomenon of skewed sex ratio (female predominance, in fetuses particularly), (7) effect of maternal age.

[Sex ratio in Down syndrome]

Data from 55 publications providing the sex ratio (SR), i.e. ratio between male and female cases of Down syndrome (DS), are presented. In general, SR was skewed toward an excess of males in the majority of studied populations, either in populations with a high level of cases ascertainment (epidemiological studies) or in selected groups. No significant correlation involving the age of either patients or mothers was found. Some other factors which might influence the sex ratio in DS at birth are mentioned. Meta-analysis of data from epidemiological studies suggests the phenomenon is not restricted to free trisomy 21 alone but appears in translocation cases, both in mutant and inherited translocation carriers (SR = 1.31 and 1.36, respectively). In contrast to nonmosaic 47, +21 cases, where SR is close to 1.3, an excess of females was observed in mosaics 46/47, +21 (SR = 0.83). No male predominance was found among patients with DS not tested cytogenetically (SR = 0.98), which may be explained by female predominance in false-positive cases. In populations with a fraction of clinically diagnosed cases of 30% and over, SR has intermediate value of 1.1. The ratio showed a tendency to increase since 1940's, reaching a mean value of 1.35 in 1980's varying from 1.3 to 1.62 in different populations), which might be a consequence of the growing use of karyotyping to confirm diagnosis and of a real increase in proportion of males. In the 1990's, the ratio fell to 1.22 varying from 1.03 to 1.27. As SR is assumed to reflect a proportion of paternal contribution, the discrepancy between the proportions of paternal errors in cytogenetic studies on parental origin of the extra chromosome (24% in the 1980's) and in molecular studies (5-10% in the 1990's) discussed in the literature might be explained by temporal changes alone. Genetic mechanisms of male predominance in trisomy 21 are reviewed, among them models for joint segregation of chromosome 21 and Y chromosome in spermatogenesis, and the chromosome 21 nondisjunction during 2nd meiotic division of oogenesis caused by Y chromosome-bearing spermatozoa.

[Reproductive behavior and Down syndrome]

Coital rates and contraception practice were investigated in mothers of 160 newborns with Down syndrome (DS) in comparison with the same aged (+/- 1 year) mothers of 160 healthy newborns. A considerable lowering of sexual activity is typical for parents, especially young ones, of children with DS. No relationship between parental sexual behavior and maternal hormonal dysfunction was found. Study on children sex ratio (SR) in relation to parental sexual activity revealed that the prevalence of boys in the DS children was due to the excess of boys (SR = 1.85) in the small group of children from sexually active couples. These data are discussed as evidence of association of a high coital rate with chromosome malsegregation in spermatogenesis.

[Sex ratio in Down syndrome. Estimation of chromosome 21 non-disjunction during spermatogenesis]

Derivation of a formula for determination of proportion of paternal trisomy 21 is presented. The formula can be applied for the literature data on sex ratio in the cases of paternal and maternal origin of the extra chromosome in the populations where direct studies of its origin can not be performed.

[Sex ratio in Down syndrome. Studies in patients with confirmed trisomy 21]

Male to female ratio (sex ratio, SR) for 1,329 liveborns with Down syndrome and for 178,160 newborns from the general population of St. Petersburg, Russia was determined as a function of a mother age. Male prevalence (an overall SR of 1.24) was found in children with all trisomy 21 variants except the cases with mosaicism (the ratio of 0.88). The most expressed male predominance was determined in children of mothers aged 20-24 years, where SR was 1.73 in the total group (p = 0.00003) and 1.61 in the cases with free trisomy (p = 0.0007). Some hypotheses concerning the male accumulation in this group are discussed including a suggestion that the SR deviations from the population value 1.06 might be due to different contribution of paternal chromosomal non-disjunction during spermatogenesis.

[Karyological characteristics of Down's syndrome: clinical and theoretical aspects]

These data have been collected from St. Petersburg Down Syndrome Register that comprises information on 1778 liveborn children with the Down syndrome, including three twin sets, ascertained within 1970-1996. Karyotypes were obtained in 1223 cases, of which 1119 (90.7%) displayed regular trisomy. Mosaicism was found in 44 cases (3.6%), including 21 males and 24 females, and among these one familial case of mosaicism in a daughter and in a healthy mother. Of 70 cases of translocations, 41(5.7%) were Robertsonian D ones. 21 (17 inherited, 16 de novo and 8 of unknown origin), 28 translocations of isochromosomes 21q; 21q (1 inherited translocation 21; 22, 22 de novo and 5 of unknown origin). One child received the anomaly from his 46XX/45XX, t(D;G) mother-carrier. In 6 cases, free trisomy 21 was associated with structural or numerical anomalies: 46XY,t(13;14)mat + 21 in twins, 47XY,t(C;C) + 21, 47XY,t(10;15)pat + 21, 47XY,inv(19)mat + 21, 47XX + 21/48XX + 21 + ring, 48XXX + 21. In 12 families parental mosaicism was shown or suspected. In 6 families one parent had chromosome anomaly, in three cases it was not inherited: t(15;22) and t(6;21) in mothers and an additional small marker in a father. In cases confirmed cytogenetically an increased sex ratio was shown (679 males and 551 females, SR = 1.23), but it was not shown in patients not tested cytogenetically (264 males and 275 females, SR = 0.96, different from the expected 297 males and 242 females, P < 0.01).

[O,O-dialkyl-S-bromomethylthiophosphates--inhibitors of mammalian choline- and carboxyl esterases: structure-activity relationship]

The interaction kinetics of potential pesticides, O,O-dialkyl S-bromomethylthiophosphates (RO)2P(O) SCH2Br (R = Et, i-Pr, n-Pr, n-Bu, or n-Am) with acetylcholinesterase, butyryl cholinesterase, and carboxyl esterase from warm-blooded animals was studied. All the compounds irreversibly inhibit these esterases, with k1 (M-1 min-1) being 1.8 x 10(4) - 1.9 x 10(6) for acetylcholinesterase, 2.0 x 10(6) - 4.1 x 10(7) for the more sensitive butyryl cholinesterase, and 2.3 x 10(7) - 2.3 x 10(8) and higher for the most sensitive carboxyl esterase. By using the Hansch and Kubinyi technique of multiple regression analysis, we quantitatively analyzed the relationship between the structure and inhibiting activity of these substances toward acetylcholinesterase and butyryl cholinesterase. Hydrophobic interactions were found to be important for the inhibition of both enzymes but are more pronounced in the case of butyryl cholinesterase. On the other hand, steric factors were much more significant in the inhibition of acetylcholinesterase. For both enzymes, the steric hindrances affect the phosphorylation stage of the enzyme.

[Antiesterase activity and toxicity of O,O-dialkyl-S-ethoxycarbonylbromomethylthiophosphates]

The interaction of potential pesticides, O,O-dialkyl S-ethoxycarbonylbromomethylthiophosphates (RO)2P(O)SCH(Br)COOC2H5 (R = Et, i-Pr, n-Pr, n-Bu, n-Am, or n-Hx) with the esterases of warm-blooded animals [acetylcholinesterase (ACE), butyryl cholinesterase (BCE), and carboxyl esterase (CE)] was studied. The acute toxicities of these compounds for mice were determined. All the compounds were non-hydrolyzable by CE and capable of irreversible inhibition of all these esterases with ki (M-1 min-1) of 1.2 x 10(5)-6 x 10(6), 2.0 x 10(6)-1.5 x 10(8), and 2.0 x 10(8), respectively. By using multiple regression analysis, we found that the steric factor plays a significant role in the inhibition of ACE, with the steric hindrances manifesting themselves even at the sorption stage. On the other hand, hydrophobic interactions predominate in the case of BCE, while steric properties of its substituents exert a markedly weaker effect and manifest themselves at the phosphorylation stage. We suggested the presence of an electrophilic region in the active site of ACE, which can interact with the ethoxycarbonyl group of the thiophosphates under study. The decrease in toxicities and the affinities to BCE and CE were found to correlate with an increase in the length of n-alkyl substituents of the compounds studied. This suggests that the unspecific esterases play a significant role as a buffer system in the exhibition of toxic effects by the thiophosphates under consideration.

[Mutational level of translocated variants of Down's syndrome in Leningrad (1982-1991)]

Karyological study of 644 newborns with Down's syndrome (DS) revealed 37 translocation cases (5.7%). Translocations were inherited in 8 cases, in 17 cases they were sporadic, and in 12 cases parents were not examined. Total mutation rate per gamete per generation (2.7.10) and mutation rates of D/21 and G/21 translocations in different female age groups were calculated. The obtained data are in good agreement with results of research in other world regions. Literature data on the parental origin of de novo translocations for DS are presented. The role of meiotic coorientation of nonhomologous chromosomes in anomalies of spermatogenesis is discussed.

[Increase in the incidence and risk of birth of children with Down's syndrome in Leningrad (1982-1989)]

Among 559,286 infants born in Leningrad in 1982-1989, there was revealed 744 infants (1.33/1000) with Down's syndrome (DS). The age distribution for their mothers as well as for 79,571 parturient women in the general population was investigated. The data regarding the period studied was compared with the results of a similar investigation conducted during of 1945-1961. A decrease in maternal age in the population was demonstrated. This was more pronounced for the mothers of affected infants. A 1.4- to 2.2-fold increase of birth risks for DS was found in all maternal age groups. The doubling of the risk value occurred by the age of 30-34, in contrast to 35-39 in 1945-1961.

[Polymorphism of C-heterochromatin chromosome regions in the etiology of human aneuploidy]

Cytogenetic study of the C-heterochromatic polymorphisms in 202 individuals from the Down's syndrome families and in 31 control individuals was undertaken. In 58 families the source of an additional chromosome was taken into account. It was shown that in the donors of extra chromosome, due to nondisjunction in the Ist meiotic division, the frequency of heteromorphism was higher (0.61) than in other groups: donors with the 2nd meiotic nondisjunction (0.44), partners of donors (0.48) and controls (0.46). Also, increase in heteromorphism rate was found in a group of young mothers (0.56) compared with a group of old mothers (0.45). The role of heterochromatic regions in chromosome nondisjunction is discussed from the point of view of meiotic nonhomologues coordination.

[Structural chromosomal reorganizations and mosaicism in the parents of children with Down's syndrome]

As to the authors' data 73% of women who gave birth to children with Down's syndrome (DS) (191 out of 231) were younger than 35 years. In this "young" group 191 couples were examined caryologically, 9 individuals having balanced translocations and 4 persons having mosaicism with a little trisomic clone were revealed. Mean ages of these parents are 24.3 for women and 32.5 for men. The rate of chromosome aberrations is 1.95% that is 8 times higher than in general population of newborns. 0.85% of examinees had heavy detectable mosaicism. Hence, no less than 5.6% of families with DS child, that are not subjected to a prenatal diagnostics because of young age, have different chromosome aberrations causing high risk of birth of an abnormal child.

[Double satellites do not increase the risk of chromosome 21 nondisjunction]

The hypothesis concerning the increase of the risk of appearance of offsprings with trisomy 21 in parents having double satellite acrocentric chromosomes is checked. Chromosomes of 266 parents having offsprings with Down's disease were examined, including 73 donors of extrachromosome 21. The frequency of chromosomes with dNORs in the total and in the donor groups did not differ from that of the control group. From 42 donors of extrachromosome, who demonstrated a nondisjunction in the first meiotic division, double satellites were revealed only once. In addition, data on the frequency of Dp+ and Gp+ variants are presented and discussed.

[Characteristics of the morphology and mitotic condensation of human Y chromosomes with structural rearrangements]

Parameters of the length and mitotic condensation were investigated in the following cases of Y-chromosome aberrations: isodicentric Y(q), Y-chromosome without heterochromatic block, and Y-chromosome with satellites. In the Ydic we revealed some differences between f-block, that is located near the inactive kinetochore, and the block near the active centromere. Satellites exert no influence on the mitotic function of Y chromosome, presumably owing to the presence of C-heterochromatic material. With the absence of heterochromatic region, a decline in condensation of the non-fluorescent segment was observed in addition to a simultaneous increase in its length. The mechanism of functioning of the structural heterochromatin is discussed.

[Differential condensation of human chromosomes 9 and Y]

Some differences were observed in the mitotic condensation of regions composing human chromosomes 9 and Y: regions 9p, 9h and Y nf are characterized by an intense condensation by the end of the spiralization interval studied (the length of the repair chromosome 3 varying from 5.4 to 2.9 mkm). At the same time, the condensation of regions 9q-h (region 9q without heterochromatic block) is slowing in the initial spiralization interval (the length of chromosome 3 varying from 16.6 to 5.5 mkm). The Yf-block of Y-chromosome is condensing faster than nf-region. The condensation parameters of Q-heterochromatic blocks are most variable while the euchromatic regions are most stable. The dynamics of 9h and of f-block condensation are independent within one karyotype. Based on the data obtained we doubt the correctness of studies on linear dimensions of the constitutive heterochromatin blocks for the evaluation of its quantity in the karyotype. A possible association of differential mitotic condensation with the chromosome segregation disturbances is discussed.

[Individual and age-related characteristics of the mitotic condensation of human Y chromosome]

Three types of contraction (steady, speeding and slowing) of fluorescent (f) and nonfluorescent (nf) parts of the human Y chromosome were revealed in the spiralization interval limited by reper chromosome 3 length from 16.6 to 2.9 mkm. On the basis of regression analysis it was shown that in the initial phase of the spiralization interval studied the f-block was condensed more rapidly than the nf-region; then the speed of contraction of the latter exceeded that of the former. A decline of the Y chromosome condensation in relation to ageing was revealed. A possible chromosome segregation disturbance in gametogenesis due to senescent changes of heterochromatic regions is discussed.

[Rare structural rearrangement of the Y chromosome (Yq-,S) in the family of a boy with a sex differentiation disorder]

In an 8-year old boy with bilateral cryptorchism the heterochromatin region deletion of Y-chromosome and the satellites in its long arm were found (karyotype 46, XYq-S). The same Y-chromosome was found in proband's father. Moreover, the proband had large brilliant satellites in the chromosome 22 and a very large segment of centromeric heterochromatin in the chromosome 1; both were inherited from his mother. The abnormal Y-chromosome is, probably, due to an exchange with heterochromatin regions between an acrocentric chromosome and Y-chromosome. The combination of above peculiarities of proband's chromosome set is supposed to promote the sex differentiation disorders in embryogenesis which led to an incomplete masculinization.

[Structural polymorphism of the heterochromatin region of human Y chromosome]

A comparison of sequential stained Y-chromosomes from 13 individuals has shown that Q- and C-blocks are not identical. Several polymorphic variants of positively stained regions were revealed. These data suggest the existence of no less than 4 types of structures in the heterochromatic region of Y-chromosome, that vary independently and reflect the localization of different satellite DNA sequences: 1) this region is positively stained using both Q- and C-methods; 2) the proximal Q-negative block, positively stained by C-method; 3) the distal Q-negative block, positively stained by C-method; 4) the distal Q-positive block not revealed by C-method. For the complete revealing of heterochromatic constitution of human Y-chromosome both Q- and C-methods are needed.

[Sex differences in the frequency of individual acrocentric chromosome association in short-term human lymphocyte cultures]

When studying the satellite associations in PHA-stimulated peripherial blood lymphocytes from healthy children some sex differences were found in the association pattern of individual pairs of acrocentric chromosomes. We believe that these data may be connected with sex difference in cell cycle of stimulated human lymphocytes.