Human X-autosome translocations: differential inactivation of the X chromosome in a kindred with an X-9 translocation.

A kindred with an X-autosome translocation and differential inactivation of the X chromosome is described. The phenotypically normal mother has a reciprocal translocation [46,X,rcp(X;9) (q11;q32)] while the daughter's karyotype is unbalanced [46,X,--X,+der(9),rcp(X;9) (q11;q32)mat], indicating adjacent-two type of segregation in the mother. In the mother's cells the normal X is late replicating, while in the daughter's cells almost the entire der(9) is late replicating, indicating the presence of autosomal inactivation. The daughter's abnormal phenotype can be explained by her sex chromosomal complement and the absence of effective trisomy 9. At this stage there is no simple explanation to account for all types of inactivation patterns encountered in the 14 balanced and 15 unbalanced cases of X-autosome translocations reported to date. Selection of X inactivation is not an inherent characteristic of the X chromosome per se, and it is not dependent on the direction of chromosomal exchange, as was suggested previously. Correlation of the phenotypic and cytogenetic features of these patients suggests a pattern of X and autosomal inactivation consistent with the least amount of genotypic and phenotypic imbalance in most cases. The data are most consistent with random X inactivation followed by selection of the most viable cell line.     

Duplication of the short arm of the X chromosome in mother and daugther

An 11-year-old girl with short stature, mental retardation, and mild dysmorphic features was found to have an inverted duplication of most of the short arm of the X chromosome [dic inv dup(X)(qterp22.3: :p22.3 cen:)]. Her mother, who is also short and retarded, carries the same duplication. Fluorescence in situ hybridization with an X chromosome library, and with X centromerespecific alpha satellite and telomere probes, was useful in characterizing the duplication. In most females with structurally abnormal X chromosomes, the abnormal chromosome is inactivated. Although the duplicated X was consistently late replicating in the mother, X chromosome inactivation studies in the proband indicated that in 11% of her lymphocytes the duplicated X was active.     

Chondrodysplasia punctata with X;Y translocation

Summary We have studied a family in which the mother and her son were carriers of an X;Y translocation, der(X)t(X;Y) (p22.3;q11). The mother was of slightly short stature and had mildly short upper extremities. The son had epiphyseal punctate calcifications, mildly short extremities, a flattened nasal bridge, and mental retardation (chondrodysplasia punctata). The extra bands on the short arm of the X chromosome were identified as deriving from the long arm of the Y chromosome, using in situ hybridization with a Y-chromosome-specific DNA probe (pHY10). The chondrodysplasia punctata seen in our case may be associated with the abnormality of the distal short arm of the X chromosome caused by X;Y translocation.     

Joubert syndrome co-existing with partial Xp trisomy: review of the literature

We report a five-year-old girl who has been clinically diagnosed as Joubert syndrome. Her cytogenetic analysis showed 46,XX,der(2)add(2q37) karyotype. Cytogenetic analysis of her mother and maternal grandmother revealed a karyogram designated as 46,X,t (X;2)(p11.2;q37). The proband's derivative chromosome was further confirmed to be a translocation chromosome 2 carrying segments from chromosome X, which originated from a segregation event of the maternal grandmother's balanced translocation passed on as a balanced translocation to the proband's mother either. So far, a number of candidate genes including EN1 on 2q were analyzed for Joubert syndrome. Based on our proband's abnormal karyotype, we suggest that further mapping studies for the syndrome should also be directed towards the chromosome X segments present on the derivative chromosome 2 of our proband.     

A dynamic study in two new cases of X chromosome translocations

Summary 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 growth retardation, behavioral anomalies, and discrete facial 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,r(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.     

Cytogenetic studies in a Y-to-X translocation observed in three members of one family,with evidence of infertility in male carriers

Summary A family is reported in which the mother and two sons are carriers of a Y-to-X translocation, der(X)t(X;Y) (p22;q11). All of the three carriers have short statute and disproportion of extremities, but otherwise normal phenotype. One of the sons, the propositus, has been affected with schizophrenia. Evidence was obtained that male carriers are probable sterile; both sons aged 26 and 30 years had azoospermia and the biopsied specimens of the testis had histologic pictures showing spermatogenetic arrest. The mother was H-Y weakly positive, and the normal X chromosome was inactivated in the majority of the cells analyzed. Dermatoglyphics of the three carriers were unusual and dissimilar to the features of Turner's syndrome. The clinical and cytogenetic findings in the present study are compared with those of the previously reported familial cases, and the genetic background causing phenotypic abnormalities in the male and female carriers is discussed.     

Partial trisomies 13 and 22 due to nondisjunction of a maternal reciprocal translocation,t(13;22)(q22;q11)

Summary A family is reported in which the propositus has an extra G-like chromosome with an unusual G-banding pattern. Cytogenetic family studies showed that the mother is a carrier of a balanced reciprocal translocation t(13;22), which does not affect the size and morphology of the chromosomes involved. The propositus has a 47,XY,+der(22),t(13;22)(q22;q11) karyotype and is therefore partially trisomic for the distal third of the long arm of chromosome 13 and for a very small part of chromosome 22. The clinical findings are presented and compared with those of other reported cases of partial trisomies 13 and 22.     

An SRY-negative 47,XXY mother and daughter

Females with XY gonadal dysgenesis are sterile, due to degeneration of the initially present ovaries into nonfunctional streak gonads. Some of these sex-reversal cases can be attributed to mutation or deletion of the SRY gene. We now describe an SRY-deleted 47,XXY female who has one son and two daughters, and one of her daughters has the same 47,XXY karyotype. PCR and FISH analysis revealed that the mother carries a structurally altered Y chromosome that most likely resulted from an aberrant X-Y interchange between the closely related genomic regions surrounding the gene pair PRKX and PRKY on Xp22.3 and Yp11.2, respectively. As a consequence, Yp material, including SRY, has been replaced by terminal Xp sequences up to the PRKX gene. The fertility of the XXY mother can be attributed to the presence of the additional X chromosome that is missing in XY gonadal dysgenesis females. To our knowledge, this is the first human XXY female described who is fertile.     

Recombinant chromosome as a result of pericentric inversion of X chromosome

Summary A structural X chromosome abnormality was found in the karyotype of a tall patient with gonadal dysgenesis and with no extragenital anomalies. Based on her mother's karyotype, which showed a pericentric inversion of the X chromosome: 46,X,inv(X)(p22q24), as well as from G and R banding, we concluded that the abnormal X chromosome of our patient was a recombinant chromosome that had originated as a result of one crossing over in the inversion loop during gametogenesis in her mother. The recombinant X chromosome had a partial deletion of Xq and a partial duplication of Xp: 46,X,rec(X),dup p,inv(X)(p22q24). After BUDR incorporation, the abnormal X chromosome of the patient and that of her mother showed a late replication. The karyotype-phenotype correlation and the nonrandom inactivation of the inverted X chromosome in the mother are discussed.     

Different patterns of X inactivation in MZ twins discordant for red-green color-vision deficiency.

Two female identical twins who were clinically normal were obligatory heterozygotes for X-linked deuteranomaly associated with a green-red fusion gene derived from their deuteranomalous father. On anomaloscopy, one of the twins was phenotypically deuteranomalous while the other had normal color vision. The color vision-defective twin had two sons with normal color vision and one deuteranomalous son. X-inactivation analysis was done with the highly informative probe M27 beta. This probe detects a locus (DXS255) which contains a VNTR and which is somewhat differentially methylated on the active and inactive X chromosomes. In skin cells of the color vision-defective twin, almost all paternal X chromosomes with the abnormal color-vision genes were active, thereby explaining her color-vision defect. In contrast, a different pattern was observed in skin cells from the woman with normal color vision; her maternal X chromosome was mostly active. However, in blood lymphocytes, both twins showed identical patterns with mixtures of inactivated maternal and paternal X chromosomes. Deuteranomaly in one of the twins is explained by extremely skewed X inactivation, as shown in skin cells. Failure to find this skewed pattern in blood cells is explained by the sharing of fetal circulation and exchange of hematopoietic precursor cells between twins. These data give evidence for X inactivation of the color-vision locus and add another MZ twin pair with markedly different X-inactivation patterns for X-linked traits.     

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

Summary a 73/4-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.     

Six cases of partial duplication-deficiency 21 syndrome: 21(dupq22delp23) due to maternal pericentric inversion: inv(21)(p12;q22). A family study

Six probands, apparently not related, with a minimal phenotype of Down's syndrome were investigated between 1970 and 1984 in our laboratory. We found in all of them an identical chromosomal abnormality 46,XX or XY,-21,+ der21(dupq22delp23). The der 21 was due to aneusomie de recombinaison, each mother having an abnormal chromosome 21: inv(21)(p12;q22). The fathers' caryotypes were normal. All parents were young and healthy. Pedigrees were established in order to find a relationship between these families. Four of our probands could be related. Familial investigations are still in progress for the last two cases; the ancestors being born in the same small geographical area (within 50 km2) we think that we shall be able to establish a relationship with the others families.     

Molecular genetic and cytogenetic characterization of a partial Xp duplication and Xq deletion in a patient with premature ovarian failure

Background

The etiology of premature ovarian failure (POF) still remains undefined. Although the majority of clinical cases are idiopathic, there are possibilities of the underestimation of the most common etiologies, probably genetic causes. By reporting a case of POF with a partial Xp duplication and Xq deletion in spite of a cytogenetically 46,XX normal karyotype, we look forward that the genetic cause of POF will be investigated more methodically.

Methods

We performed a basic and clinical study at a university hospital-affiliated fertility center. The study population was a POF patient and her family. Cytogenetic analysis, FMR1 gene analysis, multiplex ligation-dependent probe amplification (MLPA), fluorescent in situ hybridization (FISH), and oligonucleotide-array based comparative genomic hybridization (array CGH) were performed.

Results

In spite of normal cytogenetic analysis in the proband and her mother and younger sister, FMR1 gene was not detected in the proband and her younger sister. In Southern blot analysis, the mother showed a normal female band pattern, but the proband and her younger sister showed no 5.2 kb methylated band. The abnormal X chromosome of the proband and her sister was generated from the recombination of an inverted X chromosome of the mother during maternal meiosis, and the karyotype of the proband was 46,XX,rec(X)dup(Xp)inv(X)(p22.1q27.3).

Conclusion

Array CGH followed by FISH allowed precise characterization of the der(X) chromosome and the initial karyotype of the proband had been changed to 46,XX,rec(X)dup(Xp)inv(X)(p22.3q27.3)mat.arr Xp22.33p22.31(216519–8923527)x3,Xq27.3q28(144986425–154881514)x1. This study suggests that further genetic investigation may be needed in the cases of POF with a cytogenetically 46,XX normal karyotype to find out the cause and solution for these disease entities.     

Partial trisomy for the distal part of the long arm of chromosome 15 due to a balanced maternal X/15 tranlsocation]

Partial trisomy for the distal part of 15q due to a balanced maternal translocation t(X;15) is described in a 21-month old girl with growth and psychomotor retardation and a cranio-facial dysmorphism ressembling that of a previously reported patient. Treatment of lymphocytes with BrdU has shown inactivation of the normal X in the mother, and inactivation of either the abnormal or the normal X in the proposita. When the abnormal X was inactivated, the extent of inactivation of the autosome was variable.     

Partial trisomy of 13(pter→q12) due to 47,XY,+der(13),t(13;22)(q12;q13)mat

Summary A 36-month-old boy presented with short stature, short neck, shield-shaped chest, and mental retardation. Chromosome analysis showed trisomy for the short arm and the proximal portion of the long arm of chromosome 13 [47,XY,+der(13),t(13;22)(q12;q13)mat]. The patient's mother has a balanced translocation between the long arms of chromosomes 13 and 22 [46,XX,t(13;22)(q12;q13)]. The patient's neutrophils showed an elevated number of nuclear projections and his fetal hemoglobin level was undetectable.     

Three interesting cases of Down's syndrome

The results of the cytogenetic study of three families that have children affected by Down's syndrome are presented. The karyotype of case 1 was 48,XY,+21,22s+,+mar; the marker chromosome had been produced "de novo". Case 2 was: 47,X,t(Xq21q), +t(21qXq); the abnormality had been produced "de novo". Case 3 was carrier of a homogeneous trisomy 21 (47,XY,+21), where the mother was carrier of a balanced translocation 13q14q. CBG, GTG, Ag-NOR, QFQ and FPG banding techniques were used to determine the origin and importance of these anomalies.     

Isodicentric X chromosome in a patient with Turner syndrome — implications for localization of the X-inactivation center

Summary Cytogenetic analyses have previously shown that the region Xq11.2–q21 is retained in all structurally abnormal X chromosomes. From these observations the conclusion has been drawn that this critical region on the proximal long arm of the X chromosome contains the locus controlling X-inactivation. Structurally abnormal X chromosomes without the X-inactivation center would allow nullisomy, disomy, or trisomy for genes on the X chromosome, and this condition is presumed nonviable. We studied a 28-year-old woman with primary amenorrhea and features of Turner syndrome who had an unusual isodicentric chromosome of the short arm of X. This patient provided us with the opportunity to more closely define the location of the X-inactivation center. High resolution chromosome analysis showed a 46,X,idic(X)(pterq13.2::q13.2pter) chromosome pattern in 94% of her cells and a 45,X complement in 6%. Replication studies showed this derivative X chromosome to be late-replicating (inactive) in all cells analyzed. DNA analysis confirmed the breakpoint of the isodicentric chromosome to be proximal to PGK1. Based on these results, the locus for the X-inactivation center can be refined to be within Xq11.2–q13.2.     

Spontaneous reactivation of the inactive X chromosome in mouse embryonal carcinoma cells

The mouse embryonal carcinoma cell line MC12 carries two X chromosomes, one of which replicates late in S phase and shares properties with the normal inactive X chromosome and, therefore, is considered to be inactivated. Since the hypoxanthine phosphoribosyl transferase (HPRT) gene on the active X chromosome is mutated (HPRT(NDASH;)), MC12 cells lack HPRT activity. After subjecting MC12 cells to selection in HAT medium, however, a number of HAT-resistant clones (HAT(R)) appeared. The high frequency of HAT resistance (3.18 x 10(-4)) suggested reactivation of HPRT(PLUS;) on the inactive X chromosome rather than reversion of HPRT(NDASH;). Consistent with this view, cytological analyses showed that the reactivation occurred over the length of the inactive X chromosome in 11 of 20 HAT(R) clones isolated. The remaining nine clones retained a normal heterochromatic inactive X chromosome. The spontaneous reactivation rate of the HPRT(PLUS;) on the inactive X chromosome was relatively high (1.34 x 10(-6)) and comparable to that observed for XIST-deleted somatic cells (Csankovszki et al., 2001), suggesting that the inactivated state is poorly maintained in MC12 cells.     

X-inactivation patterns in lymphocytes and skin fibroblasts of three cases of X-autosome translocations with abnormal phenotypes

Summary X-inactivation patterns were studied by replication analyses both in lymphocytes and skin fibroblasts of two patients carrying balanced X-autosome translocations, t(X;10)-(pter;q11) and t(X;17)(q11;q11), and one patient with an unbalanced translocation t(X;22)(p21;q11). Preferential late replication of the normal X chromosome was found in lymphocytes of both patients carrying balanced translocations and in skin fibroblasts of the patient carrying the translocation t(X;17). However, skin fibroblasts of the patient with a translocation t(X;10) showed preferential late replication of the abnormal der(X) chromosome with no spreading of late replication to the autosomal segment. In the case of unbalanced translocation t(X;22) there was preferential late replication of the der(X) chromosome both in lymphocytes and skin fibroblasts. The abnormal phenotype of the patients is discussed in relation to the observed X-inactivation patterns and the variability of the patterns in different tissues.     

Inherited Xq duplication due to a zygotic translocation t(X;X)(q23;q27)

An Xq-duplication was found in a female child with multiple malformations. The family study revealed that her mother, who has a nearly normal phenotype, carries the same duplication. The karyotype of the grandmother shows the existence of a mosaicism: 46,X,del(X) (q23)/46,X,dup(X)(q27----q23). This mosaicism can be related to a translocation t(X;X)(q23;q27) during the first cell division of the zygote.