Presumptive evidence of two active X chromosomes in somatic cells of a human female

A complex rearrangement associated with sex reversal and the Wolf-Hirschhorn syndrome: a cytogenetic and molecular study

We report a male infant referred with multiple congenital abnormalities consistent with the Wolf-Hirschhorn syndrome. Cytogenetic analysis showed a chromosome complement of 46,XX with a deletion of 4p15.2----4pter and its replacement by material of unknown origin. The patient was positive for a number of Yp probes including SRY, the testis determining factor, and in situ hybridisation localised the Yp material to the tip of the short arm of one X chromosome. Using pDP230, a probe for the pseudoautosomal region, and M27 beta, which recognises a locus in proximal Xp, the material translocated on to 4p was identified as originating from the short arm of the paternal X chromosome. The most reasonable explanation for this complex rearrangement is two separate exchange events involving both chromatids of Xp during paternal meiosis. An aberrant X-Y interchange gave rise to the sex reversal and an X;4 translocation resulted in additional, apparently active Xp material and a deletion of 4p which produced the Wolf-Hirschhorn phenotype.

Physical mapping of 60 DNA markers in the p21.1----q21.3 region of the human X chromosome

Using a panel of human/rodent somatic cell hybrids and human lymphoblast lines segregating 18 different human X-chromosome rearrangements and deletions, we have assigned 60 DNA markers to the physical map of the X chromosome from Xp21.1 to Xq21.3. Data from Southern blot hybridization and polymerase chain reaction (PCR) amplification assign these markers to 15 primary map intervals. This provides a basis for further long-range cloning and mapping of the pericentromeric region of the X chromosome.

Localization of the X inactivation centre on the human X chromosome in Xq13

X-chromosome inactivation results in the strictly cis-limited inactivation of many but not all genes on one of the two X chromosomes during early development in somatic cells of mammalian females. One feature of virtually all models of X inactivation is the existence of an X-inactivation centre (XIC) required in cis for inactivation to occur. This concept predicts that all structurally abnormal X chromosomes capable of being inactivated have in common a defineable region of the X chromosome. Here we report an analysis of several such rearranged human X chromosomes and define a minimal region of overlap. The results are consistent with models invoking a single XIC and provide a molecular foothold for cloning and analysing the XIC region. One of the markers that defines this region is the XIST gene, which is expressed specifically from inactive, but not active, X chromosomes. The localization of the XIST gene to the XIC region on the human X chromosome implicates XIST in some aspect of X inactivation.

Isodicentric X chromosome in a moderately tall patient with gonadal dysgenesis: lack of effect of functional centromere on inactivation pattern

An isodicentric X chromosome (46, X idic (X)(pter leads to qter::qter leads to pter)) with a single functioning centromere was found in all lymphocytes and fibroblasts examined from a female patient 171.5 cm in height presenting with primary amenorrhoea. Replication of the abnormal chromosome was consistently late. In some cells the pattern was asymmetrical but the asymmetry did not appear to relate to the position of the active centromere.

Inherited partial X chromosome duplication in a mentally retarded male

A mentally retarded male patient with a structurally abnormal X chromosome is reported (karyotype 46, dir dup (X)(p11.2 leads to p21.2)Y). In the normal mother a similar X chromosome duplication was found, which was preferentially inactivated. Xg blood groups were studied in the family. The findings indicated that recombination took place at maternal meiosis, as both karyotypically normal sons and the proband were Xg(a-), the mother being Xg(a+). Functional X chromosome disomy may explain clinical abnormalities in reported patients with X duplication and a normal Y chromosome.

A complex chromosome rearrangement resulting in trisomy 15q22 to qter

A black infant with malformations was found to have trisomy 15q22→qter. The mother had a complex chromosomal rearrangement involving three chromosomes (5, 13, and 15). A comparison with previously published cases of trisomy for distal 15q suggests a pattern of clinical findings including retardation in growth and development, microcephaly, asymmetrical facies, prominent occiput, antimongoloid slant of the palpebral fissures, micrognathia, prominent nose, and congenital heart disease.

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.

Translocation (X;6) in a female with Duchenne muscular dystrophy: implications for the localisation of the DMD locus

A female with Duchenne muscular dystrophy who was a carrier of a balanced translocation t(X;6)(p21;q21) is reported. Four other previously described (X;A) translocations associated with DMD share with the present case a breakpoint at Xp21. The extremely low probability of five independent (X;A) translocations having a breakpoint at Xp21 points to a non-rand association of this site with the DMD phenotype. A DMD locus at Xp21 could be damaged by the translocation, giving rise to Duchenne muscular dystrophy. Alternatively, a pre-existing DMD gene could weaken the chromosome, favouring breaks at Xp21.

Multiple active X chromosomes in myelofibrosis with myeloid metaplasia

A woman with myelofibrosis and myeloid metaplasia had a karyotype of 47,X,del(X)(q22),+del(X)(q22) in unstimulated peripheral blood and bone marrow aspirate cultures. The normal X chromosome was late replicating, and the two deleted X chromosomes always replicated early and synchronously. The karyotype from phytohemagglutin-stimulated peripheral blood cultures was uniformly 46,XX. Structurally abnormal X chromosomes are exceedingly rare in myeloproliferative disease. The abnormal karyotype very likely reflects monoclonal proliferation of an abnormal myeloid cell line. The X chromosome inactivation process, which acts upon embryonic somatic cells of all mammals, apparently does not react to postembryonic nondisjunction of the active X chromosome.

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

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.

Gonadal dysgenesis in a patient with an X;3 translocation: case report and review

A patient with primary amenorrhoea and absence of secondary sex characteristics was found to have a balanced X;3 translocation. This phenotype is reported in approximately one-third of the balanced X;autosome translocation cases. The normal X chromosome is inactive in the present case which is in agreement with most of the similar cases. A review of the 66 balanced X;autosome translocations reported to date is presented.

A dynamic study in two new cases of X chromosome translocations

The authors discuss the clinical and cytogenetic problems raised in two new cases of X-chromosome translocations. The first case involves a child who presented marked malformations at age 3 months. Chromosome analysis revealed the presence of a translocation between a 22 and X chromosome resulting in partial X monosomy and partial trisomy 22: 46,X,der(X),t(X:22)(q112;q13)mat. The balanced translocation form was detected in the mother. Dynamic study after 5-Brdu treatment revealed inactivation of the translocated X chromosome in the proband, while in the mother the normal X chromosome was inactivated. In addition to magnesium dependent hypocalcemia resulting from a specific absorption anomaly, Case 2 presented discrete malformations and psychomotor retardation. Chromosome analysis revealed an apparently balanced translocation between a 9 and X chromosome: 46,X,t(9;X)(q12;p22). Treatment with 5-Brdu demonstrated that the translocated X chromosome was inactivated but that inactivation did not extend to the translocated part of chromosome 9. Finally, a pericentric inversion of a 9 chromosome was detected in the father, grandfather, and brother of the proband.