The origin of human trisomy: a study of heteromorphisms and satellite associations

Induced Pluripotent Stem Cell (iPSC) Lines from a Family with Resistant Epileptic Encephalopathy Caused by Compound Heterozygous Mutations in SZT2 Gene

Mutations in the SZT2 gene have been associated with developmental and epileptic encephalopathy-18, a rare severe autosomal recessive neurologic disorder, characterized by psychomotor impairment/intellectual disability, dysmorphic facial features and early onset of refractory seizures. Here we report the generation of the first induced pluripotent stem cell (iPSC) lines from a patient with treatment-resistant epilepsy, carrying compound heterozygous mutations in SZT2 (Mut1: c.498G>T and Mut2: c.6553C>T), and his healthy heterozygous parents. Peripheral blood mononuclear cells were reprogrammed by a non-integrating Sendai virus-based reprogramming system. The generated human iPSC lines exhibited expression of the main pluripotency markers, the potential to differentiate into all three germ layers and presented a normal karyotype. These lines represent a valuable resource to study neurodevelopmental alterations, and to obtain mature, pathology-relevant neuronal populations as an in vitro model to perform functional assays and test the patient’s responsiveness to novel antiepileptic treatments.

Exposure index of methyl isocyanate (MIC) gas disaster and a comprehensive spectrum of cytogenetic analysis after 30 years

Severity of clinical expression and high mortality could not facilitate establishing exposure index/association following MIC disaster in Bhopal. Mortality-based exposure stratification was critiqued by the International Medical Commission on Bhopal (IMCB). IMCB stratified exposure considering distance as surrogate at 2 km intervals after 10 years. The first follow-up cytogenetic screening of the pre-screened survivors after 30 years has demonstrated chromosome abnormalities (CA). Exposure stratification was attempted considering cytogenetic screening conducted during 1986-1988. Elevation of CA appeared proportional to exposure status and authenticated the initial mortality-based stratification. The one-on-one comparison of the previous and present cytogenetics has described the individual response to MIC exposure over 30 years. Chi-square test has been carried out for checking the cytogenetic changes at the individual level statistically, which revealed that differences of chromosomal aberrations collected immediately post-disaster and 30 years later are nonsignificant. The prominence of interindividual variation was noticed in general. The impact of overall exposure was higher in males. Constitutional abnormalities in 8.5% of the study population, including translocation, inversion, deletion, fragile sites, etc., necessitate screening of blood-linked members. The incidence of acrocentric association was prominent in the study population. Normal karyotype in children born to severely exposed parents with congenital anomalies indicates necessity of molecular karyotyping and/or screening of mutations. The study highlights follow-up of the health of the index cases at shorter (3-6 months) intervals. This comprehensive spectrum of cytogenetic report highlights immediate post-disaster chromosomal aberrations, the changes that occurred over 30 years in conjunction with other environmental factors at the individual level, constitutive genomic aberrations, polymorphic variations, and chromosomal patterns in congenitally malformed children of the survivors, which collectively indicate the possibility of acquisition/persistence of stable aberrations in MIC-exposed lymphocytes through interaction with environmental/biological confounders.

Trisomy 21: conference report and 1990 update

The most relevant data and stimulating ideas presented and discussed at the symposium are briefly summarized. They centered around four major foci: the genotype, the phenotype, the pathogenesis of Down syndrome (DS), and the Down person. The molecular genetic approaches to the isolation of genes encoded by chromosome 21, the definition of a possible "critical region," and the acquisition of further insights on the origin of trisomy 21 were the main topics of the analysis of the genotype. The study of the phenotype concentrated essentially on three complex traits related to the nervous, immune, and hematologic systems, which show great sensitivity to developmental disturbances, with major effects on DS subjects' health and behavior. The difficulties of investigating the pathogenesis of the syndrome were outlined, but the theoretical bases for devising sound and complete experimental approaches were also delineated. Finally, the special attention that in the last decade the medical and sociopsychological sciences gave to Down persons was also underlined, and future developments indicated. DS still remains a challenge to science and medicine; however, from the symposium emerged a less pessimistic view on actual potentialities for a decisive advancement in its basic knowledge.

Origin of extra chromosome 21 in 343 families: cytogenetic and molecular approaches

As the knowledge of parental origin and meiotic stage of nondisjunction is the prerequisite to evaluation of the possible etiological factors in trisomy 21, we have examined 343 families with at least one Down syndrome child. Of these, 322 were primary trisomies, including 24 mosaics, and 21 were structural rearrangements. This study was carried out by analysing chromosome 21 cytogenetic heteromorphisms and molecular RFLPs. In our study first maternal meiotic nondisjunction (75.3%) is the most common mechanism leading to primary trisomies. In the 24 mosaic cases, the most frequent error occurred at the first meiotic division (83%). The origin of structural rearrangements was maternal in 15 of 21 cases. Trisomy 21q21q was due to an isochromosome, and not to a translocation.

Pericentric inversion of chromosome 9: prevalence in 300 Down syndrome families and molecular studies of nondisjunction

The incidence of Down syndrome (DS) families where one of the parents is an heterozygous carrier of pericentric inversion of the heterochromatic region of chromosome 9-inv(9) (qh) - was determined in 3 independent groups of 100 families each. The total number of 17 such families found in the sample is significantly greater than the expected number of 5.73 for a sample of non-DS families of equal size. Consequently, the statistical association of the presence of inv (9) (qh) in one parent with the birth of a DS offspring, and the correlative 3-fold increased risk of a DS child for such families, seem to be demonstrated. A study of the origin of nondisjunction, using restriction fragment length polymorphism (RFLP) segregation analysis with a sufficient number of chromosome 21 specific probes, has provided complete information in 7 of 8 available families. Although the statistical interpretation of the results is not straightforward, due to the small size of the sample, the observed data do not contradict the assumption that the presence of inv (9) (qh) in a parent increases, by a factor of about 3, the chance that the offspring will inherit an extra chromosome 21 from that parent. Nevertheless, gathering further data appears desirable because stronger evidence would have relevance both for clinical implications and for the understanding of the function of heterochromatin, particularly with respect to meiotic and mitotic processes.

Predictive value of hormone measurements in maternal and fetal complications of pregnancy

Intrauterine tissues (placenta, amnion, chorion, decidua) express hormones and cytokines that play a decisive role in maternal-fetal physiological interactions. The excessive or deficient release of some placental hormones in association with gestational diseases may reflect an abnormal differentiation of the placenta, an impaired fetal metabolism, or an adaptive response of the feto-placental unit to adverse conditions. This review is focused on the applicability of hormone measurements in the risk assessment, early diagnosis, and management of pregnancies complicated by Down's syndrome, fetal growth restriction, preeclampsia, preterm delivery, and diabetes mellitus. Combined hormonal tests or the combination of hormones and ultrasound may achieve reasonable sensitivity, but research continues to simplify the screening programs without sacrificing their accuracy. Only in a few instances is there sufficient evidence to firmly recommend the routine use of hormone tests to predict maternal and fetal complications, but the judicious use of selected tests may enhance the sensitivity of the risk assessment based solely on clinical and ultrasound examination.

Mitotic recombination among acrocentric chromosomes' short arms

Routine Q-banding chromosome analysis detected the jumping behaviour of bright fluorescent chromosome 22 satellites (22s+) in two unrelated males (case 1 ascertained for recurrent abortions and case 2 for infertility), and in the mother of one of them, all with a normal karyotype. The 22s+ was present in more than 90% of the cells. In a minority of the cells the polymorphism was present alternatively on another acrocentric, on one chromosome 22 and on another acrocentric, on both chromosomes 22 or it was absent. We take these findings as evidence of mitotic exchanges between the short arms of the acrocentric chromosomes. The presence of a stable 22s+ in the fibroblasts of case 1 and in the lymphocytes of his son indicates that acrocentric short arm exchanges depend both on the type of tissue and on the genetic content of all the other acrocentrics.

Detection of the heteromorphic spectrum of heterochromatin in the human genome by in situ digestion using restriction endonuclease AluI

A battery of selective banding techniques has been utilized to identify the heteromorphic markers in the human genome. The recent addition of the AluI/Giemsa (G)-technique has helped not only in identifying the variable sites, but in characterizing their heteromorphic spectra. In the present investigation, we classified the pericentromeric heterochromatin by the AluI/G-technique by its size and position using 50 normal individuals and suggested the potential uses of this banding technique over earlier methods.

Acrocentric interconnections and NOR variants in human lymphocytes

Acrocentric interconnections and NOR (nucleolus organizer region) variants are frequently observed in silver-stained metaphase preparations from lymphocytes of phenotypically normal individuals. The types of interconnections and of NOR variants are outlined. It is speculated that the satellite acrocentrics (both normal and variant) are the consequence of breakage and recoiling of these interconnections. Awareness of these two features of the human genome may facilitate understanding of the NOR/nucleolus interaction(s) in such important processes as nucleolus formation and in development and/or diagnosis of disease states (i.e., malignancy).

High degree of satellite association and decreased nucleolar organizer activity in cystic fibrosis subjects

The effect of colchicine at concentrations of 0.25 X 10(-6) M, 1.0 X 10(-6) M, and 2.0 X 10(-6) M on the degree of satellite association (SA) was estimated in phytohemagglutinin-stimulated lymphocytes of individuals in the following groups: cystic fibrosis (CF) children, obligatory CF heterozygotes, control children, and control adults. In all four groups increasing colchicine concentration caused a higher degree of SA. The degree of SA differed between the two control age groups (children vs adults) only at the lowest concentration. CF patients had a significantly higher degree of SA than CF heterozygotes and than control individuals at all colchicine concentrations; CF heterozygotes had a significantly higher degree of SA than control adults at the low and intermediate concentrations. There was a strong interaction between genotype and colchicine concentration: the differences between the CF patients and the control individuals were most distinct at the intermediate concentration and between the carriers and the control individuals at the low colchicine concentration. Colchicine had no effect on the activity of the nucleolar organizer regions (NORs), as measured by the frequency of the silver-stained NORs (AgNORs), while the frequency of AgNORs in CF patients was significantly lower as compared to control individuals. Yet, the increase in the degree of SA caused by the CF mutant allele involved specifically the satellited chromosomes carrying active NORs.

Analysis of nucleolar organizing regions in parents of trisomic spontaneous abortions

Nucleolar organizing region (NOR) variants of parents of karyotyped spontaneous abortions were examined to test the hypothesis that double NORs are important in the genesis of acrocentric trisomies. We were unable to detect any significant difference in the frequency or types of NOR variants between parents of acrocentric trisomies and parents of other types of spontaneous abortions, nor did we identify a double NOR in either group. Thus, it seems unlikely that double NORs are of major significance in the etiology of acrocentric trisomies.

Chemically induced aneuploidy in mammalian cells: mechanisms and biological significance in cancer

A growing body of evidence from human and animal cancer cytogenetics indicates that aneuploidy is an important chromosome change in carcinogenesis. Aneuploidy may be associated with a primary event of carcinogenesis in some cancers and a later change in other tumors. Evidence from in vitro cell transformation studies supports the idea that aneuploidy has a direct effect on the conversion of a normal cell to a preneoplastic or malignant cell. Induction of an aneuploid state in a preneoplastic or neoplastic cell could have any of the following four biological effects: a change in gene dosage, a change in gene balance, expression of a recessive mutation, or a change in genetic instability (which could secondarily lead to neoplasia). To understand the role of aneuploidy in carcinogenesis, cellular and molecular studies coupled with the cytogenetic studies will be required. There are a number of possible mechanisms by which chemicals might induce aneuploidy, including effects on microtubules, damage to essential elements for chromosome function (ie, centromeres, origins of replication, and telomeres), reduction in chromosome condensation or pairing, induction of chromosome interchanges, unresolved recombination structures, increased chromosome stickiness, damage to centrioles, impairment of chromosome alignment, ionic alterations during mitosis, damage to the nuclear membrane, and a physical disruption of chromosome segregation. Therefore, a number of different targets exist for chemically induced aneuploidy. Because the ability of certain chemicals to induce aneuploidy differs between mammalian cells and lower eukaryotic cells, it is important to study the mechanisms of aneuploidy induction in mammalian cells and to use mammalian cells in assays for potential aneuploidogens (chemicals that induce aneuploidy). Despite the wide use of mammalian cells for studying chemically induced mutagenesis and chromosome breakage, aneuploidy studies with mammalian cells are limited. The lack of a genetic assay with mammalian cells for aneuploidy is a serious limitation in these studies.

Differences between cystic fibrosis and normal cells in the degree of satellite association

The degree of satellite association was found to be significantly higher in phytohemagglutinin (PHA)-stimulated lymphocytes from cystic fibrosis (CF) patients than from those of control individuals. PHA-stimulated lymphocytes from obligatory heterozygotes for the CF mutant allele showed an intermediate degree of satellite association. The degree of satellite association was estimated by the frequency of cells exhibiting associations, by the number of associations per cell, and by the number of chromosomes in an association. The differences in the degree of satellite association were dependent on the concentration of colchicine used for cell arrest. These findings may assist in developing a diagnostic method for the early identification of heterozygotes for the CF allele and for prenatal detection of CF homozygous fetuses.

Repeated first-trimester pregnancy loss: evaluation and management

The clinical management of repetitive first-trimester pregnancy loss is handicapped by inadequate answers to four fundamental questions. These questions center around understanding the true scope of the problem, differentiating between euploidic and aneuploidic loss, identifying the parental source of the gametogenic error, and clarifying the role of molecular developmental mutants in euploidic abortion. In spite of these limitations a diagnostic and therapeutic program is outlined for couples with repetitive early abortion. Informational gaps are identified and the future role of molecular biology in clarifying some of these issues is optimistically outlined.

Investigation of human chromosome polymorphisms by scanning electron microscopy

Human chromosome polymorphisms were investigated by scanning electron microscopy (SEM). Centromeric heterochromatin was of a constricted morphology. The extent of the C banded region was demarcated by a prominent circumferential groove in G banded chromosomes. Circumferential grooves were observed within the heterochromatin of chromosome 9, and the number of grooves present reflected the size of the region. Three dimensional viewing of satellites and short arms of acrocentric chromosomes, from different angles in the SEM, provided the opportunity for accurate assessment of the size of satellites to be made. Also, small morphological variations were defined in the SEM when definition was uncertain in the light microscope (LM).

Parental origin of autosomal trisomies

Chromosome heteromorphisms of parents and their trisomic spontaneous abortions were compared in an attempt to determine the parental origin of 204 single trisomies, including cases of trisomy 3, 4, 9, 13, 14, 15, 16, 21 and 22, nine mosaic trisomies and nine double trisomies. Non-disjunction at maternal meiosis I was the most likely source of the additional chromosome for all trisomies studied, including the mosaics, and this was the case at all maternal ages. However, trisomy 21 had a significantly increased proportion of paternally derived cases by comparison with all other trisomies. Consideration of the sex ratio in cases of trisomy 21 of known parental origin suggests that there is an excess of males associated with paternal first meiotic division non-disjunction. The fact that this mechanism of origin is more prevalent in trisomy 21 may well explain why there is an excess of males associated with this abnormality but not with other autosomal trisomies.

Chromosome heteromorphism analysis in cases of disputed paternity

Blood test results, using standard procedures, failed to exclude the alleged father as the biological father of a child in a case of disputed paternity. Using 21 different systems, the probability of exclusion for the man was 98.19%, and the probability of paternity was only 93.90% with a paternity index of 15.48. Chromosome heteromorphisms of all three individuals were studied. By comparison of fluorescent markers of chromosomes 13, 14, 15, 21, and 22, the child was shown to inherit one homologue of each of these chromosomes from the mother, but none were like the heteromorphisms of the alleged father. This excluded him as the biological father.

Trisomy 21: origin of non-disjunction

The Q-band heteromorphisms of chromosome 21 were used in a sample of 48 families with a Down's syndrome child to evaluate the origin of non-disjunction. The parental origin and the meiotic error were determined in 27 families, and in eight families only partial information was obtained. Paternal and maternal origin of non-disjunction was in a 1:3 ratio. Failures were five times more frequent in first than in second meiotic division in both sexes. The mean parental age and environmental factors in relation to the origin of the anomaly are discussed. Our results are compared with those obtained previously in similar studies by other authors.

Parental origin of the extra chromosome in Down's Syndrome

In 11 studies of patients with Down's syndrome and their parents non-disjunction was maternal in 306 cases and paternal in 77 cases. In 258 families, parental origin could not be conclusively determined. The percentage of paternal failures varied between 4.3 and 35.3% in different studies. When the type of non-disjunction was compared to the type of meiotic error, more males were born when the error was maternal (sex ratio 0.55) and more females when the error was paternal (sex ratio 0.43). An overall sex ratio of 0.52 was found. De novo translocation trisomy of type (21;21) originated paternally in one third of the cases. In (14;21) de novo translocation trisomy only one of eight cases was of paternal origin.

Marker X syndrome in an oriental family with probable transmission by a normal male

We report an oriental family with sex-linked mental retardation, macroorchidism, and a marker or fragile site on the X chromosome--mar(X)(q28). The three affected males resemble clinically most previously reported affected Caucasians. The marker was present in four female 40-70 years old, including one with normal intelligence. Transmission of the disorder appears to have taken place through a clinically normal male to his grandson.