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

Characterization of chromatin at structurally abnormal inactive X chromosomes reveals potential evidence of a rare hybrid active and inactive isodicentric X chromosome

X chromosome structural abnormalities are relatively common in Turner syndrome patients, in particular X isochromosomes. Reports over the last five decades examining asynchronous DNA replication between the normal X and isochromosome have clearly established that the structurally abnormal chromosome is the inactive X chromosome (Xi). Here the organization of chromatin at a deleted X chromosome, an Xq isochromosome, and two isodicentric chromosomes were examined. Consistent with previous differential staining methods, at interphase, the X isochromosome and isodicentric X chromosomes frequently formed bipartite Barr bodies, observed by fluorescence microscopy using numerous independent bona fide markers of Xi heterochromatin. At metaphase, with the exception of the pseudoautosomal region and the duplicated locus of the macrosatellite DXZ4 (if present on the abnormal X chromosome based on break points), euchromatin markers were absent from the Xi, whereas histone variant macroH2A formed reproducible banded mirror-image chromosomes. Unexpectedly, the isodicentric chromosome in 46,X,idic(X)(q28) cells, which carry a near full-length q-arm-to-q-arm fused chromosome, showed at interphase very rare instances of Xi chromatin bodies that were separated by large distances in the nucleus. Further examination using immunofluorescence and FISH support the possibility that these rare cells may represent ones in which one half of the isodicentric chromosome is active and the other half is inactive.

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 inv(X) (p22q22): ovarian dysgenesis in two sisters with del Xq and fertility in one male carrier

A recombinant chromosome with Xp duplication and Xq deletion was found in two sisters with normal height and gonadal dysgenesis. Their mother and other four relatives, including a fertile male, carried an inv(X) (p22q22); the inverted X was randomly inactivated in one female carrier. The abnormal X chromosome showed inactivation in all the examined cells. This is the tenth report of a recombinant X chromosome. A review of the literature shows that: i) most female carriers of inv(X) are phenotypically normal and fertile; ii) recombinants having short-arm duplication and long-arm deletion are associated with ovarian failure and normal or tall stature, whereas the reciprocal recombinants are compatible with fertility but cause short stature; and iii) except for one index case, all male carriers have a normal phenotype and 11 of them (from eight families) are of proven fertility. Moreover, no instance of male infertility has been documented.

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.

Familial occurrence of isodicentric X chromosomes with different breakpoints

We report two cases of an idic (X) chromosome found in relatives with Turner's syndrome. A 21-year-old female revealed a non-mosaic form of X isochromosome of the long arms with two C-band regions, i.e. dic(X)(qter----cen----p11::p11----cen----qter). Her 46-year-old aunt with Turner's syndrome had an X chromosome with long arm breakpoints at site q21 and chromosomal mosaicism, i.e. 45,X/46,X, dic(X)(pter----q21::q21----pter)(78/22). The relative rarity of reports about familial Turner's syndrome with structural abnormality may suggest a coincidence. However, it is difficult to exclude familial predisposition to X isochromosome formation in this family.

A recombinant X chromosome in a short statured girl resulting from a maternal pericentric inversion

A 7 3/4-year-old girl with short stature was found to have a recombinant (X),dup q chromosome resulting from an apparently unique pericentric inversion (X)(p11.2q26) present in her mother and maternal grandmother. The recombinant X chromosome was shown to be late replicating and the inversion X chromosome to be randomly inactivated. This appears to be only the eighth report (7 female, 1 male) of a recombinant resulting from an X pericentric inversion despite all diagnosed females having mild clinical abnormalities. Reasons for the rarity of such recombinant X chromosomes in man are examined.

Pericentric inversions. Problems and significance for clinical genetics

A review is given of the incidence, cytogenetics, and biologic relevance of pericentric inversions (pii). In 251 cases in the literature and our patients, 96 different inversion forms with different breakpoints are found. Eighteen of these cases have been observed several times in unrelated families; they are classified as types. The problem of pii in the heterochromatic regions of chromosomes 1 and 9 is especially emphasized and the investigations required are pointed out. The significance of the individual pii is checked with regard to their behavior in meiosis and their phenotypical relevance. An approximately 1:1 segregation is found. Fertility, stillbirth, and rates of abortion are not statistically altered. The gonadal findings available at present in man are reported and commented on. The occurrence of aneusomic recombinants among the live offspring of carriers shows a marked dependence on the length of the relative inversion segments. Since these are distinctly below average in inversion types, they only result in recombinants in exceptional cases. Certain pointers to an above-random common occurrence of other chromosomal aberrations are not found in families with pii. A correlation between pii and clinical symptoms likewise cannot be detected. However, in this connection it is pointed out that trisomic mosaics were observed jointly with pii(9) and pii(22). The review is completed by a brief examination of the literature concerning the significance of pii in evolution.

Pericentric X inversion in dizygotic twins who differ in X chromosome inactivation and menstrual cycle function

A 21-year-old female dizygotic twin was referred for cytogenetic evaluation because of mild mental retardation. Significant history, clinical, and physical findings included irregular menses, mildly coarse facies, and microcornea. Chromosome analysis revealed a pericentric inversion of the X chromosome, 46, X, inv (X)(p11;q22). Her twin who is phenotypically normal was also found to carry the same inversion. The twins differ significantly in X chromosome inactivation and menstrual cycle function.

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.

Duplication deficiency as the result of meiotic segregation of a maternal InV (10)

In a family a large pericentric inversion involving nearly 70% of the chromosome 10 has been segregating during three generations, giving several carriers and an affected male with the karyotype 46,XY,der(10)(10pter Leads to 10q25::10p12 Leads to 10pter)mat. The patient is trisomic for 10p except for a small segment near the centromere, and monosomic for the distal 10q26. A simple diagrammatic representation explains the behavior of the inv(10) in meiosis. The study of meiotic segregation in the present case, and the reviews of previously reported duplication-deficiencies, agree with established postulates and add some principles to the understanding of duplication deficiencies resulting from the meiotic behavior of inverted chromosomes.

X-autosome translocation with a breakpoint in Xq22 in a fertile woman and her 47,XXX infertile daughter

An unusual case is presented of a fertile woman heterozygous for a balanced X-autosome translocation t(X;12)(q22;p12) with a break-point (Xq22) in the critical region of the X chromosome. The karyotypes of her daughter, who is infertile, and one of her two sons are 47,XXX,t(X;12)(q22;p12) and 46,XY,t(X;12)(q22;p12) respectively. The literature on balanced X-autosome translocations in males and females involving both arms of the X chromosome is reviewed. All 23 of the 36 cases of females with balanced Xq-autosome translocation, that exhibited gonadal failure have a break-point between bands Xq13 and Xq26.U

Pericentric X chromosome ascertained during antenatal diagnosis

A pericentric inversion of an X chromosome [46,X,inv(X)(p11q28] with no detectable deletions was ascertained by amniocentesis for prenatal diagnosis in a 42-year-old woman. No defintive counsel could be offered as such an inversion had not been previously reported. At 1 year, the infant appears normal. These data and the review of other recently published karyotypes suggest an absence of a somatic position effect in the human X chromosome and possible biases of ascertainment or possible alternative karyotypic interpretations of some previously reported inv(X) cases.

X chromosome constitution and the human female phenotype

The correlations of abnormal X chromosome constitutions and the resulting phenotypes in the human female are reviewed. The following hypotheses put forward to explain these correlations are discussed in detail: (1) The damage is done before X inactivation; (2) An effect is exerted between reactivation of the X chromosome(s) and meiosis in oocytes; (3) A recessive gene(s) in hemizygous condition might be expressed in the cases in which the same X is active in all cells; (4) A change in the number of presumed active regions on the inactive X chromosomes might have an effect; (5) A position effect, in that the region Xq13-q27 has to be intact in both X chromosomes to allow normal development, may be responsible; (6) An effect during the period when cells with different inactivation patterns compete is a probability; (7) The original X inactivation may be neither regular nor random. The conclusion reached is that the phenotypic effects of a specific X chromosome aberration may be simultaneously exerted through different pathways (Tables 1 and 2). Hypotheses (2), (4), (5), and (6) are considered probable. Hypothesis (3) has been discarded, and there is very little evidence for hypotheses (1) and (7).

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.