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

Turner Syndrome: An Update

Turner syndrome is the most common sex chromosome abnormality in women. Infertility and short stature are the most striking findings seen in these patients. Unfortunately, many girls are still being diagnosed too late and therefore early diagnosis and treatment key. Turner syndrome affects many systems of the body; therefore, a comprehensive approach is key for therapeutic intervention.

Craniofacial morphology and dental maturity in children with reduced somatic growth of different aetiology and the effect of growth hormone treatment

Children with reduced somatic growth may present various endocrinal diseases, especially growth hormone deficiency (GHD), idiopathic short stature (ISS), chromosomal aberrations, or genetic disorders. In an attempt to normalize the short stature, growth hormone (GH) is administered to these children. The aim of this literature review was to collect information about the craniofacial morphology and dental maturity in these children and to present the existing knowledge on the effect of GH treatment on the above structures.

This review demonstrated that regardless of the origin of the somatic growth retardation, these children show similar craniofacial features, such as short length of the cranial base and the mandible, increased lower facial height, retropositioned mandible, and obtuse gonion angle. On the other hand, dental maturation does not demonstrate a specific pattern. Except for the above findings, muscle alterations seem to be present in individuals with short stature, who present low body muscle mass and strength, while studies on their craniofacial muscles seem to be lacking. After GH administration, the exact amount and pattern of craniofacial growth is unpredictable; however, the facial convexity decreases, mandibular length increases, and posterior facial height increases, while tooth eruption remains unaffected. Thus, it is of great importance to gain more insight into the craniofacial growth of treated and untreated children with reduced somatic growth so that the influence of GH therapy on the various craniofacial structures could be ascertained and proper orthodontic treatment could be selected.

Molecular cytogenetic characterization of two Turner syndrome patients with mosaic ring X chromosome

PURPOSE

In the present study, we reported two cases of TS with mosaic ring X chromosome showing common clinical characteristics of TS like growth retardation and ovarian dysfunction. The purpose of the present study was to cytogenetically characterize both cases.

METHODS

Whole blood culture and G-banding were performed for karyotyping the cases following standard protocol. Origin of the ring chromosome and degree of mosaicism were further determined by fluorescence in situ hybridization (FISH). Breakpoints and loss of genetic material in formation of different ring X chromosomes r (X) in cases were determined with the help of cytogenetic microarray.

RESULTS

Cases 1 and 2 with ring chromosome were cytogenetically characterized as 45, X [114]/46Xr (X) (p22.11q21.32) [116] and 45, X [170]/46, Xr (X) (p22.2q21.33) [92], respectively. Sizes of these ring X chromosomes were found to be ~75 and ~95 Mb in cases 1 and 2, respectively, using visual estimation as part of cytogenetic observation. In both cases, we observed breakpoints on Xq chromosome were within relatively narrow region between Xq21.33 and Xq22.1 compared to regions in previously reported cases associated with ovarian dysgenesis.

CONCLUSIONS

Our observation agrees with the fact that despite of large heterogeneity, severity of the cases with intact X-inactive specific transcript (XIST) is dependent on degree of mosaicism and extent of Xq deletion having crucial genes involved directly or indirectly in various physiological involving ovarian cyclicity.

Perspectives in Pediatric Pathology, Chapter 5. Gonadal Dysgenesis

One of the most challenging areas in pediatric testicular pathology is the appropriate understanding and pathological diagnosis of disorders of sexual development (DSD), and in particular, the issue of gonadal dysgenesis. Here we present the main concepts necessary for their understanding and appropriate classification, with extensive genetic correlations.

Gene analysis in patients with premature ovarian failure or gonadal dysgenesis: A preliminary study

OBJECTIVE

The aim of this study was to evaluate the presence of mutations in the coding region of the QM gene and fragile X in patients with premature ovarian failure and gonadal dysgenesis.

METHODS

After approval by the local Ethics Committee, blood samples, in EDTA, of 100 normally ovulating women, 23 with premature ovarian failure (POF) and 14 with gonadal dysgenesis 46XX, aged less than 40 years, were screened for mutation in the QM gene coding region. All patients with POF have 46, XX karyotype and serum levels of follicle-stimulating hormone (FSH) over 30 mIU/mL. In addition, all samples from patients with premature ovarian failure underwent analysis for fragile X.

RESULTS

The QM gene located at a hotspot region (Xq28) showed five points of mutations in a patient with premature ovarian failure. Four of them were able to change the amino acid sequence of the protein. None of our patients were diagnosed as having pre or mutant X fragile syndrome.

CONCLUSION

Our study suggests that Xq28 (QM gene) may be involved in ovary failure. However, further studies are needed to confirm this hypothesis.

Severe phenotype resulting from an active ring X chromosome in a female with a complex karyotype: characterisation and replication study

We report on the characterisation of a complex chromosome rearrangement, 46,X,del(Xq)/47,X,del(Xq),+r(X), in a female newborn with multiple malformations. Cytogenetic and molecular methods showed that the del(Xq) contains the XIST locus and is non-randomly inactivated in all metaphases. The tiny r(X) chromosome gave a positive FISH signal with UBE1, ZXDA, and MSN cosmid probes, but not with a XIST cosmid probe. Moreover, it has an active status, as shown by a very short (three hour) terminal BrdU pulse followed by fluorescent anti-BrdU antibody staining. The normal X is of paternal origin and both rearranged chromosomes originate from the same maternal chromosome. We suggest that both abnormal chromosomes result from the three point breakage of a maternal isodicentric idic(X)(q21.1). Finally, the phenotype of our patient is compared to other published cases and, despite the absence of any 45,X clone, it appears very similar to those with a 45,X/46,X,r(X) karyotype where the tiny r(X) is active.

Study on the relationship between cytogenetics and phenotypic effect in Turner's syndrome

The cytogenetics and clinical stigmata in 5 cases of Turner's syndrome were studied. Three of them were non-mosaic 1(Xq) and two with partial monosome of a X chromosome short are (Xp21), whose DNA replication patterns of inactive X chromosome were analyzed by RBG technique. Results showed that differences between the replication patterns in cases of X chromosome deletion (Xp21) and normal females existed; that the behavior of abnormal X expressed nonrandom inactivation. It was suggested that the phenotype may be closely related with both X chromosome replication pattern and its inactivation behavior, which might be useful in genetic counselling.

Turner syndrome in a mother and daughter: r(X) and fertility

A patient with mosaic Turner syndrome and normal fertility had three documented pregnancies. She had a 45,X/46,X,r(X) karyotype and did not undergo spontaneous sexual maturation and menarche. Conception occurred while on hormone replacement therapy. Her first pregnancy ended with the birth of a normal 46,XY male, while the third pregnancy resulted in a healthy 45,X/46,X,r(X) female. A review of the literature reveals a myriad of theories to account for the variability of ovarian function in Turner syndrome, but, as yet, there are insufficient data to yield any conclusions. There appears to be an increased risk of trisomy 21 in the offspring of females with Turner syndrome.

Molecular and cytogenetic studies of an X;autosome translocation in a patient with premature ovarian failure and review of the literature

We have identified a patient with premature ovarian failure (POF) and a balanced X;autosome translocation: 46,X,t(X;6)(q13.3 or q21;p12) using high-resolution cytogenetic analysis and FISH. BrdU analysis showed that her normal X was late-replicating and translocated X earlier-replicating which is typical of balanced X;autosome rearrangements. Molecular studies were done to characterize the breakpoint on Xq and to determine the parental origin. PCR probes of tetranucleotide and dinucleotide repeat polymorphisms, and genomic probes were used to study DNA from the patient, her chromosomally normal parents and brother, and somatic cell hybrids containing each translocation chromosome. The translocation is paternally derived and is localized to Xq13.3-proximal Xq21.1, between PGK1 and DXS447 loci, a distance of 0.1 centimorgans. A "critical region" for normal ovarian function has been proposed for Xq13-q26 [Sarto et al., Am J Hum Genet 25:262-270, 1973; Phelan et al., Am J Obstet Gynecol 129:607-613, 1977; Summitt et al., BD:OAS XIV(6C):219-247, 1978] based on cytogenetic and clinical studies of patients with X;autosome translocations. Few cases have had molecular characterization of the breakpoints to further define the region. While translocations in the region may lead to ovarian dysfunction by disrupting normal meiosis or by a position effect, two recent reports of patients with premature ovarian failure and Xq deletions suggest that there is a gene (POF1) localized to Xq21.3-q27 [Krauss et al., N Engl J Med 317:125-131, 1987; Davies et al., Cytogenet Cell Genet 58:853-966, 1991] or within Xq26.1-q27 [Tharapel et al., Am J Hum Genet 52:463-471, 1993] responsible for POF.(ABSTRACT TRUNCATED AT 250 WORDS)

Deletions of Xq and growth deficit: a review

A critical review of the literature disclosed 44 cases with a 46,X,Xq- karyotype without apparent mosaicism. Of these, 17 were of normal height (compared to the respective population), 11 had a height of over 1 SD below the mean, and 16 had a height of over 2 SD below the mean with breakpoints between Xq13 and Xq25. Since patients of normal height occurred with breakpoints as proximal as Xq13 we conclude that there is no major "growth gene" on Xq distal to q13. The most likely explanation for the variable phenotypic effect of Xq- is to assume that growth gene(s) in Xp or proximal Xq are inactivated on such a chromosome with some variability similar to the variable spreading of X inactivation seen in some X-autosome translocations.

Familial Turner syndrome

A 28-year-old Turner female with secondary amenorrhea is described, who showed 45,X/46,X,del(Xp) mosaicism in her blood lymphocytes and a 46,X,del(Xp) karyotype only in her ovaries. 45,X/46,XX mosaicism was found in the patient's mother, who presented short stature, mild Turner dysmorphism and had a normal reproductive life-span. Phenotypic implications of the cytogenetic findings in the patients are discussed, and literature data on fertility in Turner syndrome are briefly reviewed.

Turner syndrome and its variants

Turner syndrome is suspected in females with short stature, gonadal dysgenesis, and lymphedema; however, there are no pathognomonic features of Turner syndrome, and the disorder should be considered in any girl with short stature or delayed puberty. This article discusses the natural history of Turner syndrome and complications that occur in various organ systems; it reviews the physical features and complications seen with various karyotypic changes in Turner syndrome. Age-specific screening and therapies are covered.

Distal long arm deletions of the X chromosome and ovarian failure

A mother and daughter are described with premature menopause and deletion of the X chromosome at q28.

Male infant with ichthyosis, Kallmann syndrome, chondrodysplasia punctata, and an Xp chromosome deletion

We report on a male infant with X-linked ichthyosis, X-linked Kallmann syndrome, and X-linked recessive chondrodysplasia punctata (CPXR). Chromosome analysis showed a terminal deletion with a breakpoint at Xp22.31, inherited maternally. This patient confirms the localization of XLI, XLK, and CPXR to this region of the X chromosome and represents an example of a "contiguous gene syndrome." A comparison of the manifestations of patients with CPXR, warfarin embryopathy, and vitamin K epoxide reductase deficiency shows a remarkable similarity. However, vitamin K epoxide reductase deficiency does not appear to be the cause of CPXR. We propose that CPXR may be due to a defect in a vitamin K-dependent bone protein such as vitamin K-dependent bone carboxylase, osteocalcin, or matrix Gla protein.

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.

Short stature: a common feature in Duchenne muscular dystrophy

In a retrospective growth evaluation, which included parental height, birth length and a longitudinal analysis of growth and bone maturation, it has been shown that short stature is a common finding in Duchenne muscular dystrophy already in an early or even preclinical stage. Normal length and weight at birth, slow subsequent growth with a curve crossing the centiles in the 1st years of life, and normal bone maturation are characteristic of this type of short stature.

Fertility with deletion Xq25: report of three cases; possible exceptions for critical region hypothesis

We report on an Arab family in which a mother and two of her daughters, despite having deletion Xq25, are fertile. So far, only one case of deletion Xq25 associated with fertility has been reported. Consistent inactivation of the deleted X chromosome in the proposita and early menopause in the mother were noted. The effect of Xq deletion on fertility and the CRH is discussed.

Long arm deletions of the X chromosome and their symptoms: a new case (bp q24) and a short review of the literature

The clinical and cytogenetic data from a 26-year-old female with del(X)(q24----ter) are reported. This breakpoint has not been described yet. Besides this report we give a comparative summary of 24 cases from the literature with different deletions of Xq.

Inherited chondrodysplasia punctata due to a deletion of the terminal short arm of an X chromosome

We studied two families with an inherited deletion of the short arm of an X chromosome (Xp) in which affected male offspring have epiphyseal stippling in infancy (chondrodysplasia punctata), nasal hypoplasia, ichthyosis, and mental retardation. The presence of ichthyosis and the apparent pattern of X-linked recessive inheritance prompted investigation of the short arm of the X chromosome through studies of genetic markers and focused cytogenetic analysis. Biochemical studies suggested that there was a deletion of three genes previously mapped to the X-chromosome short arm, including the steroid sulfatase locus, the Xg locus, and the M1C2X locus. Prometaphase chromosomes demonstrated a deletion of Xp at p22.32 in the affected boys, in their obligate-carrier mothers, and in 11 of 25 women at risk as potential carriers. The women carrying the Xp deletion had normal gonadal function and fertility but were shorter than the noncarriers in their families (P less than 0.00001). These findings have implications for the genetic organization of this portion of the human X chromosome and demonstrate that small cytogenetic abnormalities may account for disorders with apparent mendelian patterns of inheritance.

The phenotypic effects of small, distal Xq deletions

The effects of small, distal Xq deletions (Xq26----qter) have been reviewed in light of three cases of our own and five from the literature. The symptoms caused by such deletions range from apparently none through irregular menstruation to secondary amenorrhea (or premature menopause) to primary amenorrhea. That the abnormal chromosome has any effects when it is inactivated may best be explained by one or by a combination of the following hypotheses. (1) the Xq-chromosome might exert an effect during development when cells in which it is active compete with cells in which it is inactivated, assuming that the inactivation of the two X chromosomes is originally random. (2) a more probable hypothesis is that there is a position effect when a break has occurred in the critical region Xq13----q27 which apparently must be intact in both X chromosomes to allow normal development of the ovaries. (3) this position effect might, in turn, affect the oocytes (and thus the ovary) after the inactive X chromosome is reactivated before meiosis or the deletion as such might have a direct effect on the ovaries.

X long-arm deletions. A review of non-mosaic cases studied with banding techniques

A woman with secondary amenorrhoea and an X long-arm deletion (pter----q21:) is described and compared with 30 adult non-mosaic, banded cases. Approximately 50% of the patients had gonadal dysgenesis associated with a higher frequency of short stature and "Turner stigmata" than in women with indication of ovarian activity. It is suggested that preservation of bands Xq26----28 may be decisive for normal ovarian function.

Reduced fertility in women with X chromosome abnormality

One patient with the karyotype 46,X,del(X)(p11.23) and three patients with 45,X/46,XX mosaicism were fertile or showed normal ovarian function. The patient with the Xp deletion has two daughters with the same chromosomal abnormality. A study of these patients and of others reported in the literature indicated that fertility of patients with X chromosomal abnormality has a markedly shorter duration than fertility of the normal female. Menopause commonly occurred during the second and third decade of age. We suggest that such fertility is related to the rate of germ cell attrition and hypothesize that germ cell attrition in the human female is influenced by genes of multiple effect which are carried on the X chromosome. The more of these genes which are present the slower the rate of germ cell attrition.

Cytogenic investigation of 103 patients with primary or secondary amenorrhea

Cytogenetic investigations were carried out on 103 women presenting with either primary (n = 88) or secondary (n = 15) amenorrhea. A sex chromosome anomaly was found in 26% and 33% of these patients, respectively. Other studies on women with primary amenorrhea have found a similar or even higher percentage of patients with an abnormal karyotype. It is therefore suggested that all women with absence of menstruation after the age of 16 years should be investigated cytogenetically. The surprisingly high percentage of pathological karyotypes among the secondary amenorrhea group does indicate that sex chromosome anomalies cannot be ruled out in women who have had apparently normal ovarian function for at least some time, and therefore more patients from this group should be selected for chromosome analysis.

Cytologic and molecular analysis of 46,XXq- cells to identify a DNA segment that might serve as a probe for a putative human X chromosome inactivation center

Cloned human X chromosome-specific DNA segments, derived from a recombinant phage library enriched for the human X and previously localized to different regions of the X, were used as probes in Southern blots to confirm the nature of a deletion of the long arm of the X chromosome as del(X)(q13) in a patient with some features of Turner's syndrome and suspected from cytologic studies to have a 46,XXq- karyotype. Two dimensional scanning densitometry of autoradiograms of the Southern blots was used to quantitate hybridization of the 32P-labeled probes, reinforcing visual analysis and permitting distinction between sequences present at one or two copies per diploid genome. Once thus characterized, DNA from the patient's cells was used in quantitatively analyzed Southern blots to refine the location of an additional DNA segment, previously mapped to somewhere in the proximal part of the long arm of the X chromosome, to the juxtacentromeric region of Xq, which has been hypothesized to be critical for X-inactivation. Cloned DNA probes such as that localized to the juxtacentromeric region of Xq should be useful for evaluating this hypothesis.

The origin of inverted tandem duplications, and phenotypic effects of tandem duplication of the X chromosome long arm

Tandem repeats of chromosome material can arise as inverted or as direct duplications. Such duplications of the X chromosome are instructive regarding X-linked genetic determinants of phenotype. We describe a 40-year-old woman with a direct duplication Xq13.3 to Xq27.2, short stature, gonadal dysgenesis, and secondary amenorrhea. Comparison of her phenotype with that of two other women with a direct duplication of part of Xq confirms the existence of statural determinants within the region X13 to Xq21, determinants of ovarian function within X22 to X27, and the X inactivation center within or proximal to band Xq13.3. In humans, direct duplications are more frequent than inverted, but both forms are rare. The mean age of parents is normal in subjects with direct duplications, but is advanced in subjects with inverted duplications. An inverted duplication can arise from a three-break rearrangement that includes a U-type exchange; a similar origin (two breaks and a U-type exchange) and a parental age association can be postulated for dicentric inverted duplications including dicentric isochromosome X.

Brief clinical report: del(X) (q26) in a phenotypically normal woman and her daughter who also has trisomy 21

We present a phenotypically normal woman with del(X)(q26) with no evidence of mosaicism, who had two pregnancies resulting in two live-born infants. Her first child had trisomy 21 Down syndrome and the del(X)(q26). To our knowledge, this woman is the first known case of presumably nonmosaic del(Xq) producing live-born infants. This finding can be explained on the basis of persistence into adulthood of germ cells in ovaries of the rare del(Xq) individuals. The normal phenotype in this woman supports the hypothesis that the absence of genes of middle Xq segment (q13 leads to q26) is responsible for the somatic manifestations of the Ullrich-Turner syndrome. Our finding suggests that prenatal diagnosis should be offered not only to pregnant women with numerical X chromosome abnormalities, as suggested previously, but also to those with structural X chromosome abnormalities, because of the possibility of chromosome aberrations in the offspring of such women.

Fertility in patients with X chromosome deletions

Three fertile, non-mosaic patients with partial monosomy of an X-chromosome (two with Xp deletion with breakpoints at Xp1106 and Xp2101, respectively, and one with a del(Xq25)) were found among 12 females with Xp deletion and three with Xq deletion investigated in this laboratory after the advent of banding techniques. Four phenotypically normal children resulted from a total of seven pregnancies in these women. Three of the children were chromosomally normal and one girl presented the same del(Xp) as her mother. The possibility of having genotypically and phenotypically normal offspring should be taken into account in the management and genetic counseling of children and females with X-chromosome deletions.