Familial x/x translocation: t(x;x)(p22;q13)

De novo dup p/del q or dup q/del p rearranged chromosomes: review of 104 cases of a distinct chromosomal mutation

We compiled 104 constitutional de novo or sporadic rearranged chromosomes mimicking recombinants from a parental pericentric inversion in order to comment on their occurrence and parental derivation, meiotic or postzygotic origin, mean parental ages, and underlying pathways. Chromosomes involved were 1-9, 13-18, 20-22, and X (64 autosomes and 40 X chromosomes). In the whole series, mean paternal and maternal ages in cases of paternal (proved or possible; n=29) or maternal (proved or possible; n=36) descent were 31.14 and 28.31 years, respectively. Rearranged X chromosomes appeared to be of paternal descent and to arise through intrachromosomal non-allelic homologous recombination (NAHR), whereas rec-like autosomes were of either maternal or paternal origin and resulted from mechanisms proper of non-recurrent rearrangements. Except for some mosaic cases, most rearranged chromosomes apparently had a meiotic origin. Except for 8 rearranged X chromosomes transmitted maternally, all other cases compiled here were sporadic. Hence, the recurrence risk for sibs of propositi born to euploid parents is virtually zero, regardless of the imbalance's size. In brief, recombinant-like or rea chromosomes are not related to advanced parental age, may (chromosome X) or may not (autosomes) have a parent-of-origin bias, arise in meiosis or postzygotically, and appear to be mediated by NAHR, nonhomologous end joining, and telomere transposition. Because rearranged chromosomes 10, 11, and Y are also on record, albeit just in abstracts or listed in large series, we remark that all chromosomes can undergo this distinct rearrangement, even if it is still to be described for pairs 12 and 19.

Apparent neotelomere in a 46,X,del(X)(qter→p11.2:)/46,X,rea(X)(qter→p11.2::q21.2→qter) novel mosaicism: review of 34 females with a recombinant-like dup(Xq) chromosome

A 26-year-old woman with secondary amenorrhea and turneroid stigmata was found to have a 46,X,rea(X)(qter→p11.2::q21.2→qter)/46,X,del(X)(qter→p11.2:) mosaicism in 101 G-banded metaphases (71 and 30, respectively). The mother's karyotype was normal (the father was already deceased). A fully skewed inactivation of both abnormal X-chromosomes was documented in RBG-banded metaphases and by means of the HUMARA assay. In addition, the latter revealed that the involved X-chromosome was the paternal one. The patient's secondary amenorrhea and turneroid stigmata can reliably be ascribed to her nearly complete Xp deletion present in all cells. Thus, this observation is consistent with the well-known gradation of ovarian function depending on the Xp deletion size. We assume that the first event was an intrachromosome recombination during paternal meiosis between paralogous sequences at Xp11.2 and Xq21.2, which resulted in a fertilizing rea(X) spermatozoid. Early in embryogenesis, the rea(X) dissociated at the Xp11.2 junction point to originate the del(X), which in turn was healed by the de novo addition of telomeric repeats (the acentric Xq21.2→qter segment was lost in the process). The reverse sequence appears unlikely because it implies that the del(X) chromosome was healed only after it undergone a postzygotic interchromatid recombination and apposite segregation required to obtain the rea(X) clone. The present observation further expands the cytogenetic heterogeneity in Turner syndrome and may represent another instance of a terminal deletion healed by the de novo addition of telomeric repeats.

Recombinant X chromosome in a prenatal diagnosis

The prenatal cytogenetic study of an amniotic fluid sample of a 39-year-old female showed one X chromosome with a fragment of extra material in the short arm. The G-band pattern suggested that the extra material could be the long arm of an X chromosome. Several complementary studies were performed in order to better clarify the origin of the material. These studies included parental karyotypes, microsatellite typing and comparative genomic hybridization (CGH). The results obtained allowed us to conclude that the derivative chromosome arose de novo as a recombinant X chromosome with duplication of Xq and partial deletion of Xp. Once informed, the parents decided to continue with the pregnancy, after which a healthy girl was born with no apparent disorders.

Familial transmission of a duplication-deficiency X chromosome associated with partial Turner syndrome

A rearranged X chromosome Xqter-->q13::Xp11.4-->qter was found in a mother and her two daughters, who were affected with short stature, cubitus valgus and hypothyroidism. The mother's menstrual cycles were normal until the age of premenopause. Similar previously reported cases are considered in an attempt to explain the possible origin of this X recombinant, fertility and clinical traits.

X-to-X translocation associated with gonadal dysgenesis and discrete Turner syndrome stigmata; a case report

In this paper we report an unusual type of X-to-X translocation with a translocation of the acentric part of the short arm of the X-chromosome onto the long arm of the X-chromosome at band Xq21.1 (karyotype: 46,X,t(X;X)(q21.1;p11.3). In addition to gonadal dysgenesis this 32-year-old female presented short stature and discrete Turner stigmata.

X chromosome instability associated with familial Turner syndrome

A family with two members (two generations) exhibiting Turner syndrome is described. Cytogenetic studies on these individuals showed the presence of multiple X chromosome changes. Evidence is presented to show that the maternally inherited X chromosome is the chromosome involved in the structural alterations observed. The effect of a tendency of the maternal X chromosome to break at specific sites on the development of the Turner phenotype and abnormal karyology is discussed.

A duplication/deficient X chromosome in a girl with mental retardation and dysmorphic features

A structurally abnormal X chromosome was found in a nine year old girl with mild mental retardation and dysmorphic features. Subsequent clinical examination at 18 years of age showed tall stature and gonadal dysgenesis. Re-examination of her karyotype using a variety of banding techniques on prometaphase chromosomes allowed the identification of the abnormal chromosome as a duplication/deficient X chromosome, 46,Xder X(pter----q28::p11.2----pter). The clinical features are discussed in terms of karyotype/phenotype correlation.

Partial Turner's syndrome in four girls with Xq duplication and Xp deficiency

Four girls with some clinical symptoms of Turner's syndrome had Xq duplication and Xp deficiency, their karyotypes being 46,X,dup(X)(p113;q11), 46,X,dup(X)(p212;q211), 46,X,dup(X)(p225;q13), and 46,X,dup(X)(p222;q213). No mosaicism was found. The major clinical findings, short stature, lack of pterygium colli, and no continuous gamete production, are compared with those in three previously published cases.

Structural anomalies of the X chromosome: personal observation and review of non-mosaic cases

We describe a new case of partial deletion of the long arm of the X chromosome, found in a 24-year-old female with secondary amenorrhea; the karyotype of the proposita is 46,X,del(X)(q22). We take this opportunity to review the previously published descriptions of non-mosaic structural anomalies of the X chromosome (X isochromosomes excepted) with the goal of "testing" the recent hypothesis formulated about: (a) the existence of an X inactivation center (Therman et al. 1974b); (b) the presence of a "b" segment remaining active on Xp (Therman et al. 1976); (c) the potential importance of a critical area on Xq linked to gonadal function (Sarto et al. 1973); and (d) the presence of normal gonadal function despite and Xp terminal deletion (Fraccaro et al. 1977). We conclude that the above-mentioned theories, as well as those concerning phylogenetic evolution of sex chromosome morphology presented by Lyon (1974) and Hoo (1975), receive support from practically all of the 149 cases we compared. Regarding the features of the Turner syndrome, we propose "mapping" of the X chromosome as follows: the genes involved in gonadal function seem to be located on the proximal part of Xp and on the distal part of Xq, whereas the genes whose absence is responsible for somatic features of the syndrome may be distributed along the length of Xp and the middle section of Xq(q21-q26). Furthermore, we note some interesting analogies between the evolutional model proposed by Hoo (1975) and the map we visualize.

Phenotypically normal individuals with an inversion (X) (p22q13) and the recombinant (X), dup q

Two families are described in which there is an inv(X) (p22q13) which has been transmitted for three generations. In one family (K482), no recombinants have been recovered and the inversion can be traced to a female born in 1839. In the second family (K491), a recombinant (X), dup q, has been recovered in a normal fertile woman. In both families the inverted X appears to be carrying the Xg allele. Despite extensive family studies no common ancestor has been found for the two families. The pattern of DNA synthesis has been studied in those individuals who are karyotypically 46,X,inv(X) (p22q13) and 46,X,rec(X)dup 1, inv(X) (p22q13); the selection of the abnormal as the late synthesizing X chromosome is random in the former and total in the latter. In some cells the two long arms of the recombinant X chromosome showed asynchrony of DNA replication.

Cytogenetic and clinical studies in gonadal dysgenesis with 46,X,Xt(qter leads to p221::p223 leads to qter) karyotype: review and phenotype/karyotype correlations

Chromosome analysis by Q, R, and C banding was performed in a case diagnosed clinically as gonadal dysgenesis and the karyotype was shown to be 46,X,Xt(qter leads to p221::p223 leads to qter). Localisation of the breakpoints in the fused X chromosomes and replication studies have led to a hypothesis on the origin of the translocation. A comparison of clinical and cytogenetical findings in this and other published cases has also been made in an attempt to detect some phenotype/karyotype correlations.

Tandem duplication dup(X)(q13q22) in a male proband inherited from the mother showing mosaicism of X-inactivation

An aberrant X chromosome containing extra material in the long arm was observed in a psychomotoric retarded boy and his healthy, short-statured mother. The proband showed generalized muscular hypotony, growth retardation, and somatic anomalies including hypoplastic genitalia and cryptorchism. Chromosomal banding techniques suggested a tandem duplication of the segment Xq13 leads to Xq22. In the mother the vast majority of lymphocytes showed late replication of the aberrant X chromosome. Some of her cells, however, contained an apparently active aberrant X. Both the early- and late-replicating aberrant X exhibited late replication patterns very similar to those described for normal X chromosomes in lymphocytes. Asynchrony of DNA replication among the two segments Xq13 leads to Xq22 in the dup(X) was never observed. We consider that the clinical picture of the proband is caused by an excess of active X material.

A duplication-deficiency X chromosome in a girl with severe mental retardation

Clinical and cytogenetic findings in a 14-year-old girl with severe mental retardation and partial Turner's syndrome are reported. An anomalous X was observed in the patient's karyotype. On the basis of QFQ, GAG and RBA banding studies, an Xq duplication (q12 leads to qter) and an Xp deficiency (p22 leads to pter) were apparent in this chromosome.

Further dicentric X isochromosomes and deletions, and a new structure i(X)(pter to q2102 to pter)

A new dicentric X isochromosome i(X)(pter to q2102 to pter) of similar size to a normal X is described in a girl with gonadal dysgenesis. In this non-mosaic case with an X short arm duplication, most of the stigmata associated with Turner's syndrome were absent. This structure was compared with that of six i(Xq) and three del(X). The del(Xq) structures all possessed a regular sized C band, but in the i(Xq) this was double sized in each case. Phenotypic comparisons are made in the Xq deletions, and some presumptive short arm isochromosomes are reinterpreted as Xq deletions. Incomplete centromeric suppression is suggested as the causal mechanism of mosaicism of sex isochromosomes with 45,X cells, and it is argued that an exchange event between homologoues is an unlikely mechanism to explain sex isochromosome origin.

A girl with an end-to-end fusion of two X'S

An abnormal large chromosome was seen in the karyotype of a 3-year-old girl with features of Turner's syndrome: i.e., short stature, cubitus valgus, coarctation of aorta. With the banding technics this abnormal chromosome appears to be the result of a fusion of two X chromosomes, short arm-to-short arm. This chromosome has two regions with C-heterochromatin and is late replicating.

Turner's syndrome with a duplication-deficiency X chromosome derived from a maternal pericentric inversion X chromosome

A 31-year-old woman of short stature with severe oligomenorrhea was found to carry a duplication-deficiency X chromosome, 46,X,rec(X)dup q,inv(X)(p22q11), inherited from her mother who carried a pericentric inversion X chromosome, 46,X,inv(X)(p22q11). By a combination of autoradiography and BUdR incorporation, the duplication-deficiency X chromosome was always found to be the inactive and late replicating one. In the cultured fibroblasts with the recombinant X chromosome, some of the cells were seen to have bipartite X chromatin bodies. In the mother with inv(X), the normal and the inverted X chromosome were inactivated at random.

X-X translocation in a patient with gonadal dysgenesis and the problems of phenotype-karyotype correlations

A sex-chromatin-positive woman without stunted growth, but with primary amenorrhea, and some stigmas of pure gonadal dysgenesis had the chromosome constitution 45,X/46,Xt(X;X)(q27;q27). The abnormal chromosome formed a large Barr body and was late-labeling. The chromosome consisted of two X chromosomes attached by their long arms (end-to-end), both apparently having the partial distal deletion. Both centromeric regions showed C-staining but only one constriction. The chromosome is interpreted as an isodicentric with only one centromere functioning. Some problems of phenotype-karyotype correlations are discussed.

Women heterozygous for deficiency of the (p21 leads to pter) region of the X chromosome are fertile

A woman balanced carrier of a X/15 translocation gave birth to a balanced infertile son and three unbalanced Xp--fertile daughters. This family and the other eleven cases of Xp--fertile women found in the literature demonstrate that loss of the p21 leads to pter region of the X chromosome is compatible with fertility, probably because it leaves on Xp the region which is never inactivated.

A girl with mosaicism for a dicentric X chromosome (45,X/46,X,dic(X) (Xqter to p22::p22 to qter))

A 12-year-old girl was examined for growth retardation and a few very discrete dysmorphologic stigmata of Turner's syndrome; the genitalia were infantile yet both ovaries possessed functioning follicles. R- and C-banding techniques and Brdu treatment demonstrated a 45,X formula in 95% of lymphocytes, with 5% presenting a 46,X,dic(X) formula. Cytogenetic and clinical problems raised by this observation are discussed in relation to data from the literature.

X-short arm deletion gonadal dysgenesis in two siblings due to unique translocation (Xp-;16p+)

A family demonstrating short arm deletion of the X chromosome as a consequence of X-16 balanced translocation in the mother is reported. The two Xp- sisters exhibit clinical signs of gonadal dysgenesis, while the balanced carriers are phenotypically normal. To our knowledge this represents the only example of both the balanced carrier state for an X translocation and its genetic consequence occurring in the offspring, as well as the involvement of X-16 interchange. Literature data of 37 additional cases of verified X translocations are discussed.

BrdU-33258 Hoechst analysis of DNA replication in human lymphocytes with supernumerary or structurally abnormal X chromosomes

BrdU-33258 Hoechst techniques have been used to characterize DNA replication patterns in lymphocytes from hunam females with supernumerary or structurally abnormal X chromosomes. Fluorescence analysis permits identification of late replicating X chromosomes in a very high proportion of cells and affords a high resolution method for determining the interchange points of X-X and X-autosome translocations. Asynchrony among terminal replication patterns of multiple late replicating X chromosomes within an individual cell can occasionally be demonstrated. The arms of isochromosomes usually exhibit symmetrical fluorescence patterns, with replication terminating in bands Xq21 and Xq23 (predominant pattern) or in bands Xq25 and Xq27 (alternative pattern) in both arms. In the vast majority of lymphocytes containing a balanced X-13 or X-19 translocation, the normal X is late replicating. However, DNA synthesis in the translocation products occasionally appears somewhat delayed relative to that expected for an early replicating X, consistent with possible position effects on replication kinetics.

Fusion of two apparently intact human X chromosomes

Cytological studies have been presented from a 15-year-old girl with short stature and failure of puberty. Buccal mucosa preparations revealed X-chromatin mass approximately double in size of that of a normal female. Leukocyte metaphases suggested a two cell line composition of the patient. One population of cells conformed with 45,X chromosome distribution. The chromosome complement of her other cell line had a modal number of 46. In this cell line a "C" chromosome was replaced by an exceptionally large submetacentric chromosome. This abnormal element exhibited late DNA replicating pattern. G-banding study revealed that the abnormal chromosome was produced as a result of fusion involving telomeric ends of long arms of 2 intact X chromosomes. This translocation X was bearing 2 C-banded areas; one around the centromere and the other at the distal end of the long arm. The distal C-band area did not show any evidence for centromeric function. It appears that a centromere becomes latent in the presence of another centromere in a translocation bearing 2 total chromosomes. Such a change of state in the additional centromere is vital for the stability of the translocation chromosome.

Differences in human X isochromosomes

In this paper we describe two types of i(Xq), in three patients. A classification is proposed for at least seven different types of human i(Xq)s or X long-arm duplications described by banding in the literature. Type 1 reported here and also in the literature may be the most common. It consists of a single visible centromere, metacentric, length similar to number 3, G-banding interpreted as i(X)(qter leads to cen leads to qter), one C-band like a normal X. Type 2 reported here may not have a counterpart in the literature; it exhibits a single visible centromere, submetacentric, length similiar to number 3, extra G- and C-bands on region ql. The classification summarized in this paper implies that different breakpoints are involved in the production of human X long-arm isochromosomes or duplications. Some include duplications of short arm. Morphological differences in i(Xq)s will complicate their use for studying the effect of X chromosome structure on phenotype, unless differences are defined clearly. It seems important to resolve the question of whether these reported abnormal X chromosomes involve rearrangements between the same or two X chromosomes. We also report X chromosome defects in three generations of a family; both the mother and maternal grandmother of one 45,X,i(Xq)/45,X patient are themselves mosaics for 45,X/46,XX/46,X,r(X). This family suggests that familial predisposition to X chromosome abnormality included isochromosome formation, as well as ring formation and mosaicism.