Centric fission of chromosome no. 4 in the mother of two patients with trisomy 4p

Late-appearing pseudocentric fission event during chronic myeloid leukemia progression

Pseudocentric fission is a rare event consisting of the splitting of one functional centromere into two new products, of which only one can give rise to a functionally competent kinetochore. We report here a pseudocentric fission event within the D5Z2 alphoid subset disrupting the centromeric region of chromosome 5 in a case of chronic myeloid leukemia (CML) after treatment with imatinib and interferon. The breakage generated unequal partitioning of alpha-satellite sequences between the two fission products. One product was inserted within the long arm of chromosome 12 at band 14.3, becoming the only functional centromere of chromosome der(5). The other fission product was rearranged to form a sandwich-like dicentric--but functionally monocentric--chromosome der(6), made up of material from chromosomes 5, 12, and 6. The intercentric distance on der(6) was shown to be largely >20 Mb. To our knowledge, this is the first pseudocentric fission event described in CML. Moreover, our results confirm the susceptibility to breakage of the centromeric region of chromosome 5.

A de novo centric fission of chromosome 11 in a patient with recurrent miscarriages

We report on a de novo centric fission of chromosome 11 in a healthy female referred for chromosome analysis due to recurrent miscarriages. Both fission products were mitotically stable. This centric fission of chromosome 11 appears to have no clinical significance for this patient other than recurrent miscarriages.

Ring chromosome 18q and jumping translocation 18p in an adult male with hypergonadotrophic hypogonadism

Constitutional jumping translocations (JT) are rare, especially in phenotypically normal individuals. We report on an adult male with partial hypogonadism as the sole phenotypic abnormality with an unusual chromosome abnormality. In this patient, centric fission of chromosome 18 lead to formation of a ring 18q chromosome, while 18p formed a JT through centromere-telomere fusion with chromosome 8q (66%) or 20q (13%). In 21% of cells, the 18p fragment was missing. Fluorescent in situ hybridization revealed the presence of interstitial telomeres at the junction site of the fusion and unequal distribution of the alphoid sequences through the centric fission, leaving a small, yet functional centromere within the ring. We discuss the phenotype of the patient in light of this unusual karyotype.

Trisomy 4p and partial monosomy 18q due to paternal translocation t(4;18) (p11; q21.3)

A carrier status for balanced translocation in either of the parents increases the risk of congenital malformation in the offspring. A case of multiple congenital anomalies in a female newborn was found to be associated with trisomy 4p and partial monosomy 18q as a result of a reciprocal translocation, t(4; 18) (p11; q21.3) in the father. The clinical and cytogenetic findings are compared with characteristic features of trisomy 4p, monosomy 18q and two similar cases reported earlier.

Centric fission of chromosome 9 in a boy with trisomy 9p

A centric fission of chromosome 9 was found in a boy with trisomy 9p resulting from a de novo del (9p) and a 9p isochromosome. The patient presented with clinical findings similar to those described in previously reported cases of trisomy 9p. The cytogenetic evaluation and the molecular analysis using fluorescence in situ hybridization (FISH) with specific alphoid probe for chromosome 9 showed a karyotype of 47,XY,+del(9)(q10),+i(9p). We suggest that the mechanism leading to this situation is unusual.

Prenatal diagnosis of a stable de novo centric fission: a case report

We report on the prenatal diagnosis of a baby with a de novo centromeric fission of chromosome 21. Both fission products were mitotically stable. Follow-up chromosome analysis after birth confirmed the centromere fission. This chromosome fission appears to be without clinical significance for this patient.

Clinical manifestations of trisomy 4p syndrome

Trisomy 4p syndrome is a distinct clinical entity which was noted almost a quarter century ago by Wilson et al. [71] and later was delineated by Gonzalez and colleagues [29]. The variation in the length of duplicated segment usually associated with monosomy of other genetic material which has resulted in confusion and as a result a so-called 4p syndrome could not be recognized without cytogenetic analysis. We wish to draw the attention of clinicians to this subject by presenting the description of over 75 cases including one from our clinic and stress the point that molecular approaches are imperative to characterize this anomaly. After extensive review, it appears that patients retaining at least the distal two-thirds to the entire short arm share an overlapping phenotypic expression that constitutes pure trisomy 4p syndrome which includes prominent glabella, bulbous nose with flat or depressed nasal bridge, retrognathia, pointed chin, short neck with low hairline, enlarged ears with abnormal helix and antihelix, rocker-bottom feet with prominent heel. Arachnodactyly and camptodactyly. Molecular characterization of 4p is imperative. We have also included an extensive bibliography for clinicians who may find it useful as a single reference source for evaluating their future cases.

CONCLUSION

The 4p-syndrome is a distinct entity but without cytogenetic evaluation, the syndrome can not be recognized.

Complex karyotypic mosaicism as a result of non-disjunction and subsequent centromere fission

Karyotypic discrepancy among four different cell types is described in tissues derived from a pregnancy terminated because of chromosomal anomalies. Chorionic villus cells demonstrated 46,XX (direct preparation) and 46,XX/47,XX,+mar1 (cultured cells) karyotypes, while fetal skin fibroblasts had a karyotype of 47,XX,+18 and the placenta showed a triple mosaicism of 47,XX,+18/47,XX,+mar1/48,XX,+18,+mar2. The origin of this complex chromosomal distribution and its significance are discussed in comparison with findings in similar cases.

Types, stability, and phenotypic consequences of chromosome rearrangements leading to interstitial telomeric sequences

Using in situ hybridisation, we identified interstitial telomeric sequences in seven chromosomal translocations present in normal and in syndromic subjects. Telomeric sequences were also found at the centromeric ends of a 4p and a 4q caused by centric fission of one chromosome 4. We found that rearrangements leading to interstitial telomeric sequences were of three types: (1) termino-terminal rearrangements with fusion of the telomeres of two chromosomes, of which we report one case; (2) rearrangements in which an acentric fragment of one chromosome fuses to the telomere of another chromosome. We describe four cases of Prader-Willi syndrome with the 15q1-qter transposed to the telomeric repeats of different recipient chromosomes; (3) telomere-centromere rearrangements in which telomeric sequences of one chromosome fuse with the centromere of another chromosome. We describe two examples of these rearrangements in which not only telomeric sequences but also remnants of alphoid sequences were found at the fusion point. Instability at the fusion point of the derivative chromosome was found in the Prader-Willi translocations but we were unable to correlate this instability with culture conditions. The two subjects with the termino-terminal rearrangement and the centric fission respectively have normal phenotypes. The two patients with telomere-centromere fusions were unbalanced for the short arm of an acrocentric chromosome and had failure to thrive; one of them also had dysmorphic facies. We postulate that these phenotypes could be the result of uniparental disomy.

Partial deletion of alpha satellite DNA associated with reduced amounts of the centromere protein CENP-B in a mitotically stable human chromosome rearrangement

A familial, constitutionally rearranged human chromosome 17 is deleted for much of the DNA in its centromeric region but retains full mitotic centromere activity. Fluorescence in situ hybridization, pulsed-field gel electrophoresis, and Southern blot analysis of the residual centromeric region revealed a approximately 700-kb centromeric array of tandemly repeated alpha satellite DNA that was only approximately 20 to 30% as large as a normal array. This deletion was associated with a reduction in the amount of the centromere-specific antigen CENP-B detected by indirect immunofluorescence. The coincidence of the primary constriction, the small residual array of alpha satellite DNA, and the reduced amount of detectable CENP-B support the hypothesis that CENP-B is associated with alpha satellite DNA. Furthermore, the finding that both the deleted chromosome 17 and its derivative supernumerary fragment retained mitotic function and possess centromeric protein antigens suggests that human centromeres are structurally and functionally repetitive.

Partial deletion of alpha satellite DNA associated with reduced amounts of the centromere protein CENP-B in a mitotically stable human chromosome rearrangement

A familial, constitutionally rearranged human chromosome 17 is deleted for much of the DNA in its centromeric region but retains full mitotic centromere activity. Fluorescence in situ hybridization, pulsed-field gel electrophoresis, and Southern blot analysis of the residual centromeric region revealed a approximately 700-kb centromeric array of tandemly repeated alpha satellite DNA that was only approximately 20 to 30% as large as a normal array. This deletion was associated with a reduction in the amount of the centromere-specific antigen CENP-B detected by indirect immunofluorescence. The coincidence of the primary constriction, the small residual array of alpha satellite DNA, and the reduced amount of detectable CENP-B support the hypothesis that CENP-B is associated with alpha satellite DNA. Furthermore, the finding that both the deleted chromosome 17 and its derivative supernumerary fragment retained mitotic function and possess centromeric protein antigens suggests that human centromeres are structurally and functionally repetitive.

Pseudomosaic centric fission of chromosome 4 in amniotic cells

This paper describes a case of pseudomosaic centric fission of chromosome 4 detected in amniotic fluid cell culture. The pregnancy went to term and the newborn had a normal chromosomal constitution.

Mosaic Down's syndrome with de novo 45,XX,-21,-22,+t(21q;22q)/46,XX,-21,+t(21q;21q) rearrangement

The occurrence of mosaic Down's syndrome with two independent Robertsonian translocation cell lines is very rare. Such a patient is reported here, in whom an unbalanced Robertsonian translocation between two chromosomes 21 was detected in the majority of cells. The patient also revealed a minor cell line with a second Robertsonian translocation involving a chromosome 21 and a 22. The chromosome translocations detected in this patient were de novo in origin.

Familial centric fission of chromosome 4

A centric fission of chromosome 4 is described in the proband and his mother, both phenotypically normal. In addition, partial monosomy for the long arm or the short arm or both of chromosome 4 may have been present in two of the proband's sibs who died in infancy and childhood, respectively.

Genetic risks for familial reciprocal translocations with special emphasis on those leading to 9p, 10p and 12p trisomies

An analysis of genetic risks for reciprocal translocations is given. Data from translocation families, ascertained through unbalanced offspring with trisomy 9p, 10p and 12p, were taken from the literature. The translocations were specified according to (1) the type of trisomy, (2) the degree of resulting chromosomal imbalance (partial short arm trisomies, complete short arm trisomies, complete short arm trisomies including long arm segments) and (3) the type of disjunction (2:2 or 3:1) and segregation (adjacent-1, adjacent-2; tertiary trisomy, interchange trisomy). The risks for unbalanced liveborn offspring were high for translocations leading to partial short arm trisomies through 2:2 disjunction and adjacent-1 segregation (25-29%). They were lower for translocations leading to complete short arm trisomies through the same disjunction/segregation mechanism (5-17%). Low risks were obtained for translocations, leading through 3:1 disjunction to unbalanced offspring (about 2%). For 2:2 disjunction and adjacent-2 segregation and for 3:1 disjunction the risk is significantly lower for male than for female carriers.--The frequency of balanced karyotypes compared with normal karyotypes deviated among the phenotypically normal offspring of parental carriers from the theoretical 1:1 ratio, both for translocations ascertained through trisomy 12p and trisomy 10p.--It was demonstrated that the genetic risk for reciprocal translocations depends exclusively on (1) the degree of possibly resulting genetic imbalance and (2) the probability of the disjunction/segregation mechanism leading to this type of imbalance. Both factors can be predicted from the position of breakpoints.--The precision of breakpoint localizations and its impact on the risk estimation are also considered.--Finally, general rules for genetic counselling of families with reciprocal translocations are indicated.

Karyotypic fission theory and the evolution of old world monkeys and apes

The karyotypes of living catarrhines are correlated with the current concepts of their fossil record and systematic classification. A phylogeny, beginning at the base of the Oligocene, for those animals and their chromosome numbers is presented. Todd's (1970) theory of karyotypic fissioning is applied to this case - three fissioning events are hypothesized. A late Eocene event (the primary catarrhine fissioning) is hypothesized to underlie the diversification of the infraorder Catarrhini into its extant families, the second fissioning underlies the radiation of the pongidae/Hominidae in the Miocene and the third accounts for the high chromosome numbers (54 - 72) and the Neogene(Miocene-Pliocene-Pleistocene) radiation of members of the genus Cercopithecus. Published catarrhine chromosome data, including that for "marked" chromosomes (those with a large achromatic region that is the site for ribosomal RNA genes) are tabulated and analysed. The ancestral X chromosome is always retained in the unfissioned metacentric state. The Pongidae/Hominidae have 15 pairs of mediocentric chromosomes that survived the second fissioning whereas the other chromosomes (besides the X) are thought to be fission-derived acrocentrics. Both the detailed karyology and the trend from low to high numbers is best interpreted to support Todd's concept of adaptive radiations correlated with karyotypic fissioning in ancestral populations.

Balanced transmission of centromeric fission products in man

Centrometric fission of chromosome 10 is reported in a 25-year-old psychiatric patient and his 5 1/2-year-old normal daughter. The relevant literature on this subject is briefly reviewed.

Multibranched chromosomes 1, 9, and 16 in a patient with combined IgA and IgE deficiency

Instability of the centromeric region of chromosome 1 and multibranched configurations formed by different numbers and combinations of arms of chromosomes 1, 9, and 16 were found in cultured lymphocytes of a 12-year-old male with combined IgA and IgE deficiency. No chromosome abnormalities were found in fibroblast cultures from the patient or in blood cultures from his parents. A possible effect on the frequency of the abnormalities of the almost continuous antibiotic treatment received by the patient was found both in vivo and in vitro, but no abnormalities were found in blood cultures from control subjects who received similar treatment. Interphase association of chromosomes 1, 9, and 16 and a high frequency of interchanges among the centromeric regions of these chromosomes due to the presence of a fragile site is assumed to be the cause of the abnormalities.

Chromosomal evolution in primates: tentative phylogeny from Microcebus murinus (Prosimian) to man

The karyotypes of more than 60 species of Primates are studied and compared, with the use of almost all existing banding techniques. There is a very close analogy of chromosome banding between the Simians studied and man. The quantitative or qualitative variations detected all involve the heterochromatin. It is very likely that all the euchromatin (nonvariable R and Q bands) is identical in all the species. Approximately 70% of the bands are common to the Simians and to the Lemurs (Prosimians). In the remaining 30%, technical difficulties prevented a valuable comparison, but this does not exclude the possibility that a complete analogy may exist. Thus, it is very likely that chromosomal evolutions of the Simians, and probably of all the Primates, has occurred without duplication or deficiency of the euchromatin. Approximately 150 rearrangements could be identified and related to the human chromosomes. The types of rearrangement vary from one group (suborder, family, genus) to another. For instance, Robertsonian translocations are preponderant among the Lemuridae (44/57), but are nonexistent among the Pongidae. Chromosome fissions are very frequent amng the Cercopithecidae (10/23), but were not found elsewhere, and pericentric inversions are preponderant in the evolution of Pongidae and man (17/28). This suggest that the chromosomal evolution may be directed by the genic constitution (favouring the occurrence of a particular type of rearrangement, by enzymatic reaction), by the chromosomal morphology (the probability that Robertsonian translocation will be formed depends at least partially on the number of acrocentrics), and by the reproductive behaviour of the animals. Reconstitution of the sequence of the chromosomal rearrangements allowed us to propose a fairly precise genealogy of many Primates, giving the positions of the Catarrhines, the Platyrrhines, and the Prosimians. It was also possible to reconstruct the karyotypes of ancestors that died out several dozen million years ago. The possible role of chromosomal rearrangements in evolution is discussed. It appears necessary to consider different categories of rearrangements separately, depending on their behaviour. The 'nonfavoured' rearrangements, such as pericentric inversions, need to occur in an isolated small population for implanting, by an equivalent of genic derivation. The 'favoured' rearrangements, e.g., Robertsonian translocations, may occur and diffuse in panmictic populations, and accumulate. Their role of gametic barrier could be much more progressive. For discrimination between these two categories, it was necessary to differentiate the selective advantage or disadvantage of the rearrangement itself. It was not possible to show that chromosomal rearrangements play a direct role in modification of the phenotype by position effect. Comparison of the rearrangement that have occurred during evolution and those detected in the human population shows a strong correlation for some of them...

4p trisomy syndrome: report of 4 additional cases and segregation analysis of 21 families with different translocations

Thirty reports of partial 4p trisomy have been published. The manifestations and cytogenetic findings in four additional cases from two families are described in the present paper. Segregation analysis has been performed on the 21 families reported to date. The risk of having unbalanced offspring was the same in carrier mothers and carrier fathers. The risk of trisomic offspring was 14%. Among phenotypically normal progeny, normal karyotypes and balanced translocation states occurred with about equal frequency.

Unstable telocentric chromosome produced after centric misdivision of a 21q/21q translocated element

An unstable telocentric chromosome was found in an individual with Down's syndrome and an unusual chromosomal mosaic, 46,XX, t(21q21q)+,21-/46,XX,21q-/45,XX,21-. As the 21q/21q chromosome was of paternal origin, based on the characteristics of its centromeric heterochromatin and on the characteristics of both 21 chromosomes of the father, it was concluded that its formation involved centric breakage and loss of centromeric material. The cell line with the 21q- chromosome may have originated from the translocation by an asymmetric misdivision of the reduced centromeric material. Of the two telocentrics produced by this fracture, one, possessing the smaller amount of centromeric apparatus, would be immediately lost; the other would be retained, but complete activity of its centromere would not be restored. It would therefore be unstable and might be lost.

t(9/22) with centric fission and NOR translocation leading to a case of pure 9p trisomy in the offspring

A case of trisomy 9p originating from t(9/22) mat is reported. The rearrangement is characterized by centric fission of chromosome 9 and by translocation of NOR from chromosome 22 to 9q. The hypothesis of centric fission is discussed on the basis of various banding patterns. The case also reveals unusual knee dislocation.

Mosaicism in amniotic fluid cell cultures: classification and significance

The last decade has witnessed increasing application of human cytogenetic technology to prenatal chromosome analysis. However, unlike the rather uniform peripheral blood T-lymphocyte system which has provided most of our experience in human cytogenetics, long-term amniotic-fluid cell cultures display extreme cellular heterogeneity and disproportionate growth of certain cell types as a consequence of clonal amplification. When they enter cell culture, many of these cells are approaching the terminal stages of their respective, life spans and may have accumulated chromosomal aberrations. Concern about the possibility of true fetal mosaicism seems warranted chiefly in situations were multiple colonies display potentially viable aberrations. Clonal analysis, preferably of multiple clonal types, and attention to details of clonal morphology are likely to minimize diagnostic errors and undue apprehension resulting from mosaicism in amniotic-fluid cell cultures.

Trisomy 4p: five new observations and overview

Five new cases of trisomy of the short arm of chromosome No. 4 are presented. In two brothers the abnormality arose from segregation of the 4p chromosome present in the mother who is a carrier of a centric fission of one No. 4 chromosome. In the other three patients, the chromosome imbalance originated from segregation of a balanced maternal 3p/4q or 4/22 translocation. The available data, derived from the 4p trisomics reported so far, are adequate to establish trisomy of the short arm of chromosome No. 4 as a definite clinical entity. The most outstanding findings include growth retardation of prenatal onset, severe mental deficiency, microcephaly and a peculiar constellation of facial dysmorphisms. The dermatoglyphic patterns and the radiological findings may help towards a correct interpretation of the syndrome.

The trisomy 4p syndrome: case report and review

We report a further case of trisomy 4p: a 5-year-old mentally retarded boy with characteristic facial features, eye abnormalities, flexion contractures, several bone anomalies, and hyperactivity. In a review of 27 cases (11 male, 16 female, 22 families) the cytogenetic and clinical data were tabulated and analyzed. Diagnosis is established by karyotype: there is always partial or apparently "total" trisomy of the short term arm of chromosome 4. In 19 families a parent carried either a balanced translocation (16 times) or a pericentric inversion (3 times); 3 patients had de novo duplication of 4p. In several cases, additional deletions or trisomies were present. From the analysis of all cases, but particularly of the "pure" trisomies, the phenotypic spectrum of this condition was observed and found to be a specific multiple congenital anomaly/mental retardation (MCA/MR) syndrome. Its main features are a characteristic facial appearance, postnatal growth retardation, severe psychomotor retardation with or without seizures, microcephaly, and various major and minor anomalies.